The

Ford Flathead Engine

 

 How Too Size A Turbo-Charger For Our Application...

 

Project: Flathead is going to be Turbo-Charged, so we need to know how to choose the correct Turbo for the engine we have.  Were starting out with a Ford Flat-Head Engine, it has 235 ci, 8-Cylinders and is a 4-Stroke.

Configuration = V-8

Cubic Displacement = 235 ci

Bore = 3.1875"

Stroke = 3.750"

Ambient Temperature = 70°f

Barometer = 29.0 in Hg

Maximum RPM

                     (a) = 5,000 rpm

                     (b) = 6,000 rpm

Maximum Boost Pressure

                     (a) = 7psi

                     (b) = 14.2 psi

     I will be tracking the conditions of two separate scenario's, I think this will add Balance and allow some interesting comparisons.

 

Let's start by Converting the Displacement of our Engine from cubic inches to cubic feet

Converting the Displacement

                 235ci       =    0.1359 cu ft

         1728 cu in/cu ft

 

 Airflow Rate  - Airflow rate through an engine is referred to as cubic feet per minute (CFM) at a standard atmospheric pressure.

 

 Next we will Calculate the Ideal Volume Flow through our Engine

Ideal Volume Flow

Engine (a)

0.1359 cu ft    x  5000 rpm  =  339.75 cfm

Revolutions             2

Engine (b)

0.1359 cu ft     x  6000 rpm  = 407 cfm

Revolutions              2 

 

     These figures above are at 100% Efficiency, because of Residual Gases, Intake and Cylinder Head restrictions most Engines don't operate at 100% Efficiency, a more realistic figure for our Engine would be 80% Efficiency.

Converting to 80% Efficiency

 

Engine (a)     339.75  x  .80  =  271.8 cfm

 

Engine (b)     407  x  .80  =  325.6 cfm

 

 Another way to determine the Air Flow rate is by the following:

Airflow rate = CID x rpm x 0.5 x Ev (80%)

                                               1728

Engine (a)

Air Flow Rate  =  235cid x 5000rpm x 0.5 x 0.80

                                             1728

Air Flow Rate  =  470000     =  271.99 cfm

                              1728

 

Engine (b)

Air Flow Rate  =  235cid x 6000rpm x 0.5 x 0.80

                                             1728

Air Flow Rate  =  564000     =  326.38 cfm

                              1728

     With this method, the flow rate is in cfm and the displacement is in cubic inches.  We use .5 because the 4-stroke engine only fills the cylinders once every two  revolution, and the 1728 converts the cubic inches to cubic feet.  Both methods will work and both give the Air Flow Rates of Normal, Turbo-Charged or Super-Charged engines, based on how much air an engine will flow at 80% efficiency.

     All compressors are rated at Inlet Flow, and air entering the intake will not be at standard conditions (29.92 in Hg & 60°f)  Because of this, it is necessary to compute the actual density to determine the air flow through the turbochargers compressor.  For our application, we will consider compressor Efficiency to be 65%.  First we need to find our Pressure Ratio.

Pressure Ratio

 Pressure Ratio  =  Manifold Pressure Absolute

                       Inlet Pressure Absolute

(To convert from psi to in Hg you need to multiply by 2.03)

Engine (a)    

PR   =   (7psi x 2.03) +  29.0  =  1.49  

                                                           29.0

 

Engine (b)    

 PR   =   (14.2psi x 2.03) + 29.0  = 1.994  

                                                           29.0

 

 

 We got our (Y) figures from the Ideal Temperature Rise Chart

Engine (a)  Y = 0.121

Engine (b) Y = 0.217

 It is also necessary to add 460f to the temperatures because the calculations need to be in Absolute Temperature (degrees Rankine)

Tideal  =  Y  x T1

 

Engine (a)  Tideal  =  0.121  x (70 + 460)  = 64.13f

 

Engine (b)  Tideal  =  0.217  x (70 + 460)  = 115.01f

Actual Temperature Rise

 

Tactual =    Tideal  /  Compressor Efficiency (65%)

 

Engine (a)   =  64.13f / .65 =98.66f

 

Engine (b)   =  115.01f / .65 =176.93f

 

 Intake Manifold Temperature

 

IMT = Compressor Inlet Temperature  +  Tactual

 

Engine (a)  =  70°f  +  98.66°f  =  168.66°f

 

Engine (b)  =  70°f  +  176.93°f  =  246.93°f

 

 Notice the huge difference in Temperature between the two (2) engines?  Remember, the engines are identical, except for the higher boost and RPM levels.  Engine (b) would absolutely benefit from some sort of Inter-Cooler.

These Intake Air Temperatures may or may not actually get this hot.  There is some cooling effect from the Inter-Cooler tubing, and because fuel itself has an cooling effect on the intake air.  Project:Flat-Head will include the use of Twin-Inter-Coolers, which will substantially lower this intake Air Temperature.  But we have to figure the Theoretical Intake Air Temperature to get the Density Ratio.

Density Ratio

Turbo-Chargers produce there power by packing more air molecules into the combustion chamber.  How tight these molecules are packed into each cubic inch of volume, is refereed to as the Density of the Air Charge.

The Density Ratio is nothing more then comparing the Inlet Temperature to the Outlet temperature, and the Inlet Pressure to the Outlet Pressure.

 

Density Ratio  = 

Inlet Temperature   x   Outlet Pressure

Outlet Temperature      Inlet Pressure

 

Engine (a)   

Density Ratio  =     70 + 460      x   14.21+ 29.0

                              168.66 + 460               29.0

 

Density Ratio  =    530        x    43.21  

                              628.66            29.0

 

Density Ratio  =  0.84306   x   1.49

 

Density Ratio  =  1.256

 

 

Engine (b)   

Density Ratio  =     70 + 460      x   28.826 + 29.0

                             246.93 + 460              29.0

 

Density Ratio  =    530        x    57.826  

                              706.93            29.0

 

Density Ratio  =  0.7497   x   1.994

 

Density Ratio  =  1.494

 

Compressor Inlet Flow

Now with this piece of the puzzle solved we can calculate the Actual Compressor Inlet Flow, under these conditions.

 

Compressor Inlet Flow = Compressor Outlet Flow  x  Density Ratio

 

 

Engine (a)    

             

Compressor Inlet Flow  =  271.8 cfm  x 1.256

                                                                =   341.38cfm

 

Engine (b)    

 

 Compressor Inlet Flow  =  326 cfm  x 1.494

                                                                   =   487.04cfm

 

 

     We now have everything we need to find the Turbo-Charger that is right for our engine.  Most legitimate Turbo-Charger retailers will display the Compressor Map for each Turbo-Charger they sell, same goes for the manufacturer, they should make available each Compressor Map for the various Turbo-Chargers they sell.  With the data now "in hand", you can compare the many different Turbo-Chargers so you find one that works best for your situation. Also, when doing calculations like these that take into account the Ideal Temperature Rise, where you need the "Y" Data from a table, many times this table and it's data will be located on the manufacturers or retailers site.  If not, call them and they can provide it for you.   Most Compressor Maps are in cfm, some are in lb/min.  Too convert cfm  to lb/min  simply multiply the cfm figure by 0.069.  Also note that most Compressor Map created for lb/min, are also calculated with the Turbo-Charger at 85°f and a barometer of 28.4 in-Hg.

 

Lets look back and see what we have found

through all these calculations.                          

     On our Project Engine (a) Approximately 49% more air will be going through the engine then the engine could have consumed by itself.  Engine (b) will have approximately 99% more air.  We find this out my looking at the Pressure Ratio.  Pressure is also measured in bar, and Atmospheres (ATM) ,1 ATM = 1 bar = 14.7psi.  In engine (b) the the PR or Pressure Ratio, of 1.99 is equal to 1.99 bar.  In theory, engine (b) would have an equal power output of an engine twice the displacement !! that means our little 235 under 14.2 psi of boost, would act like a big block 470 engine at atmospheric.  Kind of like dynamite, a big bang in a small package.

 

 Project:Flat-head is going to be a Twin Turbo-Charged engine, so we need to calculate a few more items.

 

     It a huge misconception to think Twin turbo-chargers are inherently more powerful then a single turbo set-up, as too many other factors are involved.  On in-line 4-6 and 8 cylinder engines a single turbo may in-fact be the best way to go.  Usually over 350cid, and on any "V" type engine design, the dual turbo set-up is necessary.  The particular arrangement of the V-8 0r V-6 engine makes twin-Turbo's more of an attractive lay-out in terms of not only aesthetics but also thermal efficiency.  A lot of energy (heat) is lost trying to tie the two exhaust manifolds together for a single turbo lay-out.  Space and Plumbing need also be considered.

 

Turbos produce Huge amounts of Torque - and Torque is FUN!!

 

     On Project:Flat-Head we are using Twin T3/T4 T04E Turbo-Chargers.   These HYBRID turbochargers consisting of a T3 turbine section, (standard, Stage II or Stage III trim) and a T4 compressor section (T04B trim or T04E trim). The T3/T4 HYBRID’s offers the low inertia and fast boost response of the light weight T3 turbine wheel and the high airflow characteristics of the T4 compressor family, making the T3/T4 HYBRID the turbo of choice for high performance applications.  Thats all great, but what is LOW INERTIA and FAST BOOST RESPONSE ?

 

Inertia   -  The tendency of a body to resist acceleration; the tendency of a body at rest to remain at rest or of a body in straight line motion to stay in motion in a straight line unless acted on by an outside force.  Resistance or disinclination to motion, action, or change.

     On a turbo engine we have to consider the time it takes for the compressor to get going fast enough to make boost.  This small delay between the throttle opening and the engine making boost is know as Lag, and inertia has everything to do with it.  As the definition describes inertia, it's the resistance to change.  And when you open the throttle, you want change, and quickly!  Lets look at a few different scenarios.

Moment of inertia is the resistance of a rotating body to a change in speed, represented by the letter I.

I = K2M

where K is the radius of the gyration and M is the mass of the body.

     Radius of gyration is the distance from the rotating axis to the point where all the mass of the body could be located to have the same I as the body itself. 

    In other words, a 12-inch diameter turbine wheel might be represented by a ring with a diameter of 7 inches.  In this case, K = 3.5 inches.  For good rotor acceleration it is important to have the smallest moment of inertia possible.  Most turbine wheels are designed with minimal material near the outside diameter to reduce K.  The moment is proportional to the square of K, so reducing K by 1/2 will reduce 1 to 1/4 of the previous value.

Because of this, it is often to your advantage to use two (2) smaller turbos rather then one (1) larger turbo.

Example:

On Project:Flat-Head we are using two (2) turbos and the major diameter of one of the turbine wheels is 2.319" with an assumed weight of .89 lb's.  the computation works out as follows.

I = K2M

I = K2wg    1.15952  x .89lb

                       386

I = 0.003099 in-lb-sec2

 

      If we were to use a larger single turbo set-up the out come would look more like this, a single T-72 with a 4.030" turbine wheel and a weight of 1.65lb.

I = K2M

I = K2wg    2.0152  x 1.65lb

                       386

I = 0.017355 in-lb-sec2

An increase in time of over 5.6 times !!

 

Why do Turbo-Chargers make so much Power??.. And Why so much Torque??..

     Engines operate because of cylinder pressure, the amount of energy given off by the explosion of the fuel/air mixture in the combustion chamber.  For example:  a cylinder with a bore area on 10 square inches (3.569 inch bore) with 800 psi of pressure would be subject to a compressive power load of 8000 pound.  This means with that 800 psi of pressure, there would be 8000 lb of force pushing down on the piston, and it's connecting rod.  That's a lot of force.  With a Turbo-Charged engine it is very easy to surpass this 800 psi threshold.  Turbo-Charged engines can make up to 1600 psi of cylinder pressure, which is double the stock pressure.  Even at 1200 psi, you can see that the same engine with the same bore area, would now have a compressive load of 12,000 lbs.  Thats a huge amount of force pushing down on the piston.  This is why Turbos make so much torque, the extra cylinder pressure directly equates to more compressive power and that to more torque.  While turbos are famous for extra Horse-Power, It's the Torque that really makes them fun. 

Understanding an A/R Ratio  - basically the A/R is nothing more then a comparison of exhaust flow,intake volume verses discharge area.  Our A/R ratio is .63

 

T40E.50CompressorMap.gif     

This is a Compressor Map of our Turbo-Charger, you can plot the map by simply plugging in our figures.  As you will see, this Turbo will work very well for our application.

 To make any sence out of this chart, we must first convert or CFM figures to LB/MIN.  To do this we multily the CFM by 0.069.  or

LB/MIN = CFM x 0.069

Engine (a)

LB/MIN = 341.38 x 0.069 = 23.55

23.55 / 2 = 11.77 lb/min

P/R = 1.49

 

Engine (b)  

LB/MIN = 487.04 x 0.069 = 33.60

33.60 / 2 = 16.80lb/min

P/R = 1.994

     Because we are useing two (2) Turbo-Chargers, we will have to split the CFM rating or you can just split the LB-MIN rating.

 

T40E.50CompressorMap.gif

 

T3.40CompressorMap.gif

     Too plot the Compressor map simply find the right P/R on the left side of the map and the appropiate LB/MIN figure on the bottom.  Extend the two lines and where the contact each other, is the spot at which you'll find their capacity and the opperating RPM at which they will be.  It doesen't take an expert to see that the top map (which is of the compressor we have) is not exactly ideal for our engine.  By contrast, the compressor map of the much smaller T3 compressor is much closer to a match for our purposes.  To correct this, we will change out the compressor housing with a smaller T04E "40".  This will put us back into the area we need to be.

     This concluded our calculations for Project:Flat-Head, we now have everything needed to install the correct Turbo-Charger and make any necessary adjustments so the system works at it's best.  The following Definitions, Tables, formulas and Information is provided for your use and or entertainment.  Hopefully this will answer the many questions  one might have.  The following provided by Mega-Squirt, is from there website and included because they make a wonderful product that allows many people to convert from a carbureted engine to EFI at a reasonable cost, with all the advantages and adjustability of the more higher priced systems.  Don't follow the crowd and think just because a system is less expensive, that is is in some way lacking sophistication.  Mega squirt, offers everything needed to run, adjust and tune a EFI engine, turbo-charged or not, and has been proven on road-race circuits, drag strips and city streets all across the USA.

FORMULAS, DEFINITIONS and TABLES

Virtually all formulas and tables presented here have to do with how the media performs.  It's cooling efficiency, static pressure drop across the media relative to the face velocity and cubic feet per minute of air flow is the measuring rod to which we apply all other calculations and determinations.  In simpler terms, the rigid media is the heart and soul of evaporative cooling.  Without an understanding of it's operation, it is difficult to design a cooling system or size cooling equipment for a building.

The part about applications and design are covered in the section "Applications and Design" which can be reached from the Technical Data section which is available from our home page.  To keep a surprisingly complex subject simple, only the formulas and tables that relate to this media are covered in this section.

Abbreviations   and Definitions:

Let's start with some abbreviations we use in our formulas:

     AC = Air Changes   ( Usually expressed in changes per hour or per minute.  Air change is the number of times the air within a structure is exhausted and replaced during a specified period such as hour or minute).

Absolute Pressure   - This term refers to th pressure measured on the scale that has it's zero point at approximately 14.7 psi (at sea level) below atmospheric pressure.  it is a true measurement of all the pressure, rather than just the pressure above atmospheric.

 

Absolute Temperature   -  Similar to absolute pressure, absolute temperature has its zero point where no heat exists.  This is approximately 460°f below 0°f.  An absolute degree is the same size as a Fahrenheit degree.  The freezing point of water (32°f) is about 492°f above absolute zero, or 492° absolute.

 

Air/Fuel Ratio (AFR)   -  AFR is the ratio of the weight of air to the weight of fuel in a combustible mixture.  AFR is critical in the proper functioning of an engine.

 

Ambient  -  Ambient refers to the surrounding atmospheric pressure and temperature.

 

Atmospheric   - This word has recently taken on the connotation of an engine operating without any form of super-charger.  My lawn mower has an atmospheric engine.

 

Boost  -  Boost is the pressure above atmospheric, measured in the intake manifold. 

 

Boost Threshold   -  Same as Boost Point.  This is the lowest engine RPM at which the turbo-charger will increase power over the engines atmospheric equivalent.  More simply put, the lowest RPM at which noticeable boost can be achieved.

 

Bypass Valve   -  The bypass valve permits a bleed of flow around the turbo-charger when the engine is under boost.

 

     BTUH  = British Thermal Units per Hour.  A measure of heat or the absence of heat  ("cold" can be defined as the absence of heat) in a volume of air or space. BTUH is not commonly used in evaporative cooling terminology but necessary to calculate heating and mechanical refrigeration.  (It is most often used as "heat of vaporization = 1043 BTU/lb in the formula for calculating evaporation rate and standard CFM).

 

Clearance Volume   -  Combustion chamber volume above the piston at top dead center is called clearance volume.

 

 (S)CFM  = (Standard) Cubic Feet per Minute.  Usually referred to as simply CFM.  This is a necessary ingredient in any formula involving evaporative cooling.  It is a measure of air volume movement in one minute.

 

Compression Ratio   -  This is the displacement volume plus clearance volume divided by the clearance volume.

 

Compressor  -  For this writing, the compressor is the air pump itself.  The front half of the turbo-charger, through which the intake air passes.  it is also frequently refereed to as the " Cold side" of the turbo-charger.

 

Compressor Efficiency (Ec)   -  Efficiency is the ratio of what really happens to what should happen.  In the case of the compressor, measurement of the temperature gain caused by compressing the air exceeds what thermodynamic says it should be.  Compressor efficiency converts calculated temperature gains to real temperature gains.

 

Compressor Surge   -  Compressor surge occurs when the throttle is slammed shut and air is caught between a pumping turbo and the throttle plate.  This air blasts its way backward out the front of the turbo-charger.  When this happens, there is a suddenly room for more air in the manifold, and air is pumped back in my a still pumping turbo-charger.  The throttle is still closed, so the air again blast back out through the front of the turbo.  This continues until the turbo losses enough speed for leak back around the compressor to dampen the air oscillations.  Compressor surge can als occur under boost, if too much boost pressure is present with low airflow through the system.  The chirping sound heard from the turbo when lifting off the throttle while operating under boost results from the oscillating air volume.  This noise is suppressed by the bypass valve.

 

Crossover point   -  This is the point at which manifold boost pressure equals turbine inlet pressure.

 

Detonation   -  Detonation is spontaneous combustion of the air/fuel mixture ahead of the flame front.  When pressure and temperature exceeds that required for controlled combustion, the mixture auto-ignites.  The metallic pinging sound is the resulting explosion's shock wave colliding with the cylinder walls.

 

Design   -  This term is used in many ways to define the parameters of an application or specifications.  Some common uses are as follows:  IDb =  Indoor Dry Bulb.  ODb = Outdoor Dry Bulb.  IWb = Indoor Wet Bulb.    OWb = Outdoor Wet Bulb. EDb = Entering Dry Bulb.  LDb = Leaving Dry Bulb.  EWb = Entering Wet Bulb.  LWb = Leaving Wet Bulb. This term is often used in conjunction with "conditions" such as "Climate Design Conditions".  In evaporative cooling, climate data is considered to be Dry Bulb and Wet Bulb levels.  It would require a  "Psychometric Chart" to locate the juncture of the Dry Bulb and Wet Bulb lines to find the grains or pounds of moisture per pound of dry air or relative humidity (RH).  Refer to Table 1 for a psychometric chart digitalized for easy reading of relational elements of Db, Wb and RH.

 

Displacement Volume   -  is defined in several ways: 1. The swept volume of the cylinder; 2. The area of the bore times the length of the stroke; 3. Total engine displacement divided by the number of cylinders.

 

Draw-Through   -  This indicates that the throttle is on the inlet side of the turbo compressor.

 

Dry Bulb temperature (Db or DB)   -   Measurement (usually in Fahrenheit) of  temperature taken by a standard thermometer or similar thermal indicator.

 

End Gas   -  The end gas is the last part of the air/fuel mixture to burn.  It's importance to a turbo-charged engine is paramount, because it is this end gas in which detonation usually occurs.

 

External Static Pressure  -  Expressed in inches, water column.  The pressure against which the air flow must move.  The pressure external to the cooling unit opposing air flow (i.e. restrictive ductwork, etc.)

  

Fahrenheit (f or F)   -  Temperature conforming to a thermometric scale on which water boils at 212 degrees and freezes at 32 degrees.  Named after Gabriel D. Fahrenheit, 1736.

 

 Fv (or) FV = Face Velocity   - Face velocity or "air velocity" is the measure expressed in feet per minute (FPM) the air is moving at the entry side (face) of the cooling media.  This is another necessary ingredient in any formula in evaporative cooling to determine efficiency.

 

FPM = Feet Per Minute  - The measure of speed (velocity) of the air .

 

Gallons per Hour (GPH)   -  A measure of liquid (usually water) moving during one hour.  

                                  

Gallons per Minute (GPM)   - A measure of liquid (usually water) moving in one minute.

 

IN. HG   -  This phrase reads " Inches of mercury"  and is the measure of pressure on yet a different scale.  In this project, in-Hg will reefer to vacuum in the intake manifold, and the scale works downward toward atmospheric pressure.  For example, idle speed vacuum is usually about 18in.Hg, and as throttle is applied, the vacuum goes toward 0 gauge, which is atmospheric pressure.

 

Inertia   -  The tendency of a body to resist acceleration; the tendency of a body at rest to remain at rest or of a body in straight line motion to stay in motion in a straight line unless acted on by an outside force.  Resistance or disinclination to motion, action, or change.

 

Inter-cooler   -  An inter-cooler is a heat exchanger placed between the turbo and the engine to remove heat from the air exiting the turbo-charger when operating under boost.  Inter-cooler are also called charge air coolers.

 

Inter-cooler Efficiency (EI)   -  An Inter-cooler's efficiency is measured by how much heat it removes relative to the heat added by the compressor.

 

Inertial Load   -  Internal loads are those created by weight and acceleration.  A heavier piston creates a greater inertial load.  likewise, an increase in RPM means greater acceleration and, thus a greater inertial load.

 

Lag   -  Lag is the delay between a change in throttle and the production of noticeable boost when engine RPM is in a range in which boost can be achieved.

 

Lean   -  lean means not enough fuel to achieve the correct air/flue ratio for the existing conditions.

 

Non-sequential Fuel Injection   -  EFI that pulses independently of valve position is non sequential.

 

OEM   -  Original Equipment manufacturer;  the company the built it in the first place.

 

Power   -  Strictly speaking, power is the result of how fast a certain amount of work is done.  In automotive context, power is the product of torque at any specific RPM times that RPM.

 

Power Load   -  This is the load induced into all engine components by pressure created by the burning gases.

 

Pre-Detonation   -  This is a meaningless phrase and should not be included here or anywhere else.

 

Pre-Ignition   -  Pre-ignition refers to spontaneous combustion of the air/fuel mixture prior to the spark.

 

Pressure ratio   -    The ratio of absolute boost pressure to atmospheric pressure.

 

Pulse Duration   -  The amount of time, measured in thousandths of a second (msec), that an electronic fuel injector is held open on any single pulse.  Pulse duration is a relative measurement of the amount of fuel delivered to one cylinder per combustion cycle.

 

Reversion  -  Reversion occurs when some of the burned exhaust gases are pushed back into the combustion chamber and intake system during valve overlap.  This is caused by exhaust manifold pressure exceeding intake pressure or by shock waves in the exhaust ports and manifold.

 

Relative Humidity (RH)  -   Expressed in percent.  The percent of water vapor in the air compared to the amount of water vapor the same air could contain.  (i.e.  15% RH indicates the air is 15% saturated with water vapor)

 

Rich   -  A condition that exist when too much fuel is present to achieve a maximum -power air/fuel ratio.

 

Saturation Efficiency (SE)  -    This is the percent of the Wbd (Wet Bulb Depression) achieved by the cooling process.  I.E. At 100 degrees (f) Dry Bulb and 70 degrees (f) Wet Bulb, the Wbd would be 30 degrees (f).  If the actual temperature drop measured at the discharge side of the media was 73 degrees (f), the percent of saturation efficiency would be 90%.   This means that the air passing through the media has been saturated with water vapor (moisture) to 90% of its maximum.  "Cooling Efficiency" is the same as Saturation Efficiency and is most often used to define the performance level of the media.  Also called just "efficiency".

 

Sequential Fuel Injection  -  A fuel injection pulse timed to discharge fuel when the intake valve is in the most advantageous position is called sequenced.  It pulses the injectors in the same sequence as the firing order.

 

 Static Pressure Drop  -   Expressed in inches, water column.  The amount of pressure required to push the air through the media as measured with a magnehelic gage.  The difference between the pressure of the air flow at the intake of the media  and the discharge side of the media. The measure of pressure for any component through which air flow is measured at the intake and discharge.  This is an important consideration in some evaporative cooling applications.

 

Supercharge  -  To force more into an engine than the engine can breathe by itself is to supercharged it.  A supercharger is a device that does this, it may be driven by belts, gears or a turbine.  When driven by a turbine, it's called turbocharging.

 

Thermal Load   -  On this site, we will take the rather narrow definition of heat added to the system by the turbo-charger.  This comes from heat produced in the air that is compressed by the turbo and the mixture heat increase due to reversion.

 

Throttle Response   -  A change in the speed and torque of an engine brought about by change in the throttle position is called throttle response.

 

Torque  -  The amount of twisting force provided by a turning shaft is called torque.  It is measured in foot-pounds, inch-pounds and even Newton-meters.

 

Turbine  -  The turbine is a fan driven by the engine's exhaust gases.  it is often called the "hot" side of the turbo-charger.

 

Turbo-Charger   -  A turbo-charger is a super charger driven by a turbine.

 

Under Boost   -  When a system has greater than atmospheric pressure in the intake manifold, it is operating under boost.

 

Volumetric Efficiency (ev)  -  This is the ratio of the number of molecules of air that actually get into a combustion chamber to the number of molecules in an equal volume at atmospheric pressure.

 

Waste-gate  -  The waste-gate is a boost-pressure -activated valve that allows only enough exhaust gas into the turbine to achieve desired boost.  The waste-gate routes the remainder of the exhaust gas around the turbine and out the tailpipe.

 

 Water  gauge or Water Column in Inches  ( WG or w.g. or WC or w.c.)  This is a measure of static pressure.  A Pilot Tube is used to take this measurement.  The Pitot Tube is a curved (U-shaped) glass tube with a prescribed amount of water and a scale. The tube is hollow.  When air is blown into one end the water column will be forced up the other side to some level.  The level to which the column of water rises is a measure, in inches, of the pressure of the force required.

        

Wet Bulb Temperature (wb or WB)   -   The lowest temperature that can be reached by evaporatively cooling the air.  This measurement is usually taken with a "sling psychrometer".  This device is a standard thermometer with a "wet sock" over the sensor bulb.  The psychrometer is slung in a circular motion rapidly enough to cause evaporation to occur around the sensor bulb to drop the temperature to it's lowest point possible with the evaporation process.

Wet Bulb Depression (wbd or WBD)  -   The difference between the Dry Bulb and the Wet Bulb temperatures.  This temperature is the total amount of cooling available through the evaporative cooling process.  At 100% cooling efficiency, the temperature drop would be equal to the Wet Bulb Depression. Also known as Wet Bulb Differential.

 

     

     

Leaving Dry Bulb  = [ODb - (SE x (Odb-OWb)]

Leaving Wet Bulb  = Normally considered same as entering  Wb.

Wet Bulb Depression  = ODb - OWb

Evaporation Rate  = [CFM x WBd x (SE / 8700)]   ( this is simple method)

Bleed - Off Rate  = Evaporation Rate x .20 (prox)

(Recirculation) Water flow Rate  = 3 times the evaporation rate (prox)

Standard CFM  = Sensible BTU/hr / (1.08 x (IDb - Db) x Density Ratio
                           Where IDb = Indoor Design Dry Bulb (f)

CFM  = Standard CFM / Density Ratio

BTU  = CFM X Delta T x 1.08

Density Ratio  = 1.325 x Barometric Pressure / (Db(f)                                                                                

Water weight (US gallon)  = 8.33 pounds per gallon (based on distilled water)

Water volume (US gallon)  = 7.481 gallons per cubic foot

Water weight (US gallon cubic foot)  = 7.481 x 8.33 = weight of cubic foot of   water (62.288#)

Face Area  =  Width x Height of open face  area through which air will flow (expressed in square feet.)

Face Velocity  = CFM / Face Area (Sq Ft) (expressed  in Feet per minute  (FPM).    

                 

Table 1:  Psychrometric Chart  

#H20 per

#Dry Air

                  Temperature (Dry Bulb degrees f)

40

50

60

70

80

90

100

110

120

Wb RH% Wb RH% Wb RH% Wb RH% Wb RH% Wb RH% Wb RH% Wb RH% Wb RH%

.001

27

20

34

12

41

10

46

8

51

5

54

3

57

2

62

2

65

1

.002

32

40

36

28

43

19

47

12

53

10

57

7

60

5

63

4

66

2

.003

35

58

41

40

45

28

50

19

54

15

58

10

62

7

65

6

67

3

.004

36

75

43

51

47

38

52

26

56

19

59

13

63

10

66

8

69

5

.005

39

95

45

65

50

47

54

32

57

23

61

17

64

12

67

9

71

7

.006

x

x

46

78

51

55

55

39

59

27

63

20

66

15

69

10

72

9

.007

x

x

49

91

53

64

57

45

61

31

65

24

67

18

70

12

73

10

.008

x

x

x

x

55

73

59

51

63

36

66

28

68

20

71

14

74

11

.009

x

x

x

x

56

82

60

57

64

41

67

30

70

22

72

16

75

13

.010

x

x

x

x

57

90

62

63

65

46

68

33

72

25

74

18

76

14

.011

x

x

x

x

60

99

64

70

66

50

70

36

73

27

76

20

77

15

.012

x

x

x

x

x

x

65

76

67

55

71

40

74

29

77

22

78

17

.013

x

x

x

x

x

x

66

83

69

59

72

44

75

31

78

24

80

19

.014

x

x

x

x

x

x

67

90

70

63

74

47

76

33

78

26

81

20

.015

x

x

x

x

x

x

69

95

72

68

75

50

77

36

79

27

82

21

.016

x

x

x

x

x

x

70

99

73

72

76

53

78

39

81

29

83

22

.017

x

x

x

x

x

x

x

x

74

76

77

57

79

42

82

31

83

23

.018

x

x

x

x

x

x

x

x

75

80

77

59

80

45

82

33

84

24

.019

x

x

x

x

x

x

x

x

76

85

78

62

81

47

83

35

85

25

.020

x

x

x

x

x

x

x

x

77

90

80

65

82

49

84

37

86

27

.021

x

x

x

x

x

x

x

x

78

95

81

69

83

51

85

39

87

28

.022

x

x

x

x

x

x

x

x

79

99

82

72

84

53

86

40

87

29

.023

x

x

x

x

x

x

x

x

x

x

83

75

85

55

87

41

88

31

.024

x

x

x

x

x

x

x

x

x

x

84

78

86

58

88

42

90

33

.025

x

x

x

x

x

x

x

x

x

x

85

81

87

60

89

43

91

34

.026

x

x

x

x

x

x

x

x

x

x

86

85

88

62

90

44

92

35

.027

x

x

x

x

x

x

x

x

x

x

87

88

89

65

91

46

93

36

.028

x

x

x

x

x

x

x

x

x

x

88

91

90

67

92

47

94

37

.029

x

x

x

x

x

x

x

x

x

x

89

95

91

69

93

49

95

39

.030

x

x

x

x

x

x

x

x

x

x

90

99

92

71

94

51

95

40

Notes:  Db is Dry Bulb temperature,  Wb is Wet Bulb temperature, #H2o  is Pounds of moisture per pound of dry air which is a measure of absolute humidity.  RH is Relative Humidity.

Read the chart by finding the known elements, such as Dry Bulb and Relative Humidity and move horizontal to find the Wet Bulb and pounds of moisture per pound of dry air.  I.E. The weather forecast is for 100 degrees at 15% Relative Humidity.  You will find that the Web Bulb is 66 degrees and the pounds of moisture is .006 per pound of dry air.  Knowing the Wet Bulb will allow you to determine the Wet Bulb depression.  

The Psychometric chart will provide you the necessary information to design systems, predict outcomes and many other useful applications of the information!  This chart is digitalized to make it simpler to use.

It is necessary to interpolate and extrapolate accordingly for those in-between conditions not directly covered in the above chart.  I.E. if 105 degrees was the temperature to use, then it would be necessary to interpolate the available data to reach the right conclusion.  In this instance, the Wet Bulb would be 67.5 degrees.  This chart is intended to be reasonably accurate at sea level and should be within p/m 5%.  If greater accuracy is required, it is recommended that you use the proper Psychometric chart for the elevation desired or make proper adjustments for elevation (barometric pressure).

Wbd(f)

 

 Gallons Per Hour evaporated per 1000 CFM with a Saturation Efficiency of:
0.80 0.82 0.84 0.86 0.88 0.90 .092 0.94 0.96 0.98
5 0.50 0.51 0.52 0.53 0.55 0.56 0.57 0.58 0.60 0.61
10 0.99 1.02 1.04 1.07 1.09 1.12 1.14 1.17 1.19 1.22
15 1.49 1.53 1.56 1.60 1.64 1.68 1.71 1.75 1.79 1.83
20 1.99 2.04 2.09 2.14 2.19 2.23 2.28 2.33 2.38 2.43
25 2.48 2.55 2.61 2.67 2.73 2.79 2.86 2.92 2.98 3.04
30 2.98 3.05 3.13 3.20 3.28 3.35 3.43 3.50 3.58 3.65
35 3.48 3.56 3.65 3.74 3.82 3.91 4.00 4.08 4.17 4.26
40 3.97 4.07 4.17 4.27 4.37 4.47 4.57 4.67 4.77 4.87
45 4.47 4.58 4.69 4.80 4.92 5.03 5.14 5.25 5.36 5.48

To determine Gallons per Minute divide by 60.  Formula to determine evaporation rate is shown in Formulas section.

Wbd

(f)

Temperature drop (Dry Bulb) for Media Thickness of:
4" 6" 8" 12" 18" 24"
10.0

5.3

6.8

7.9

8.9

9.8

9.9

12.5

6.6

8.5

9.8 11.1 12.2 12.3
15.0

7.9

10.2 11.8 13.3 14.6 14.8
17.5 9.2 11.9 13.8 15.6 17.1 17.3
20.0 10.5 13.6 15.8 17.8 19.5 19.7
22.5 11.8 15.3 17.7 20.0 21.9 22.2
25.0 13.2 17.0 19.7 22.2 24.4 24.7
27.5 14.5 18.7 21.7 24.4 26.8 27.2
30.0 15.8 20.4 23.6 26.7 29.3 29.6
32.5 17.1 22.1 25.6 28.9 31.7 32.1
35.0 18.4 23.8 27.6 31.1 34.1 34.6
37.5 19.7 25.5 29.5 33.3 36.6 37.0
40.0 21.1 27.2 31.5 35.6 39.0 39.5

Note:  12" thick media @ 500 FPM face velocity is the preferred design .  This is the best trade-off between performance and cost.

Temp. Elevation/Inches Hg
 (f) 0/

29.92

1000/

28.86

2000/

27.82

3000/

26.82

4000/

25.84

5000/

24.90

6000/

23.98

7000/

23.09

8000/

22.22

9000/

21.39

10000/

20.58

68 1.00 0.97 0.93 0.90 0.87 0.84 0.80 0.77 0.75 0.72 0.69
70 1.00 0.96 0.93 0.90 0.86 0.83 0.80 0.77 0.74 0.71 0.69
72 1.00 0.96 0.93 0.89 0.86 0.83 0.80 0.77 0.74 0.71 0.69
74 0.99 0.96 0.92 0.89 0.86 0.83 0.80 0.77 0.74 0.71 0.68
76 0.99 0.95 0.92 0.89 0.85 0.82 0.79 0.76 0.73 0.71 0.68
78 0.99 0.95 0.92 0.88 0.85 0.82 0.79 0.76 0.73 0.70 0.68
80 0.98 0.95 0.91 0.88 0.85 0.82 0.79 0.76 0.73 0.70 0.68

 

Leaving Air

Temp (LDb)

                    Temperature over

outside ambient

                    Air Changes

Per Hour

   
Over 78 (f)  

20+

 

30-60

76f to 78f  

15 to 20

 

20 to 40

74f  to 76f  

10 to 15

 

15 to 30

72f  to 74f  

5 to 15

 

12 to 20

Less than 72f  

Less than 10

 

10 to 15

Notes:  The "Air Change" method is a practical approach to assist in the determination of the size and efficiency of evaporative cooling equipment required for the structure.  The principle behind this method is to determine the difference between the inside temperature of the structure, without using evaporative cooling and the outside ambient temperature during its highest condition.  While this method is ideal for existing structures, new structures not yet built can be estimated on the same scale.

Leaving Air Temperature reflects the output of the evaporative coolers whether existing or planned.  The air change column indicates a range of frequency and is used in determining air volume requirements.  Other criteria are needed to complete the sizing of equipment.  Refer to the section on "Applications and Design" for more specific information on equipment sizing.

 

Acronyms / Terminology

  A/R   
A/R describes a geometric characteristic of all compressor and turbine housings. It is defined as the inlet cross-sectional area divided by the radius from the turbo centerline to the centroid of that area.
  • Compressor A/R - Compressor performance is largely insensitive to changes in A/R, but generally larger A/R housings are used to optimize the performance for low boost applications, and smaller housings are used for high boost applications. Usually there are not A/R options available for compressor housings.
  • Turbine A/R - Turbine performance is greatly affected by changing the A/R of the housing. Turbine A/R is used to adjust the flow capacity of the turbine. Using a smaller A/R will increase the exhaust gas velocity into the turbine wheel, causing the wheel to spin faster at lower engine RPMs giving a quicker boost rise. This will also tend to increase exhaust back pressure and reduce the max power at high RPM. Conversely, using a larger A/R will lower exhaust gas velocity, and delay boost rise, but the lower back pressure will give better high RPM power. When deciding between A/R options, be realistic with the intended vehicle use and use the A/R to bias the performance toward the desired power-band.
  Choke Line   
 
The choke line is on the right hand side of a compressor map and represents the flow limit. Properly sizing a turbo is important to prevent the compressor from operating past the choke line. When a turbocharger is run deep into choke, turbo speeds increase dramatically while compressor efficiency plunges (very high compressor outlet temps). Additionally, the turbo's durability is compromised by the resulting high thrust loads.
 
  CHRA   
 
(Center Housing & Rotating Assembly)
The CHRA is essentially a turbocharger minus the compressor and turbine housings
 
  Clipped Turbine Wheel   
 
When an angle is machined on the turbine wheel exducer (outlet side), the wheel is said to be "clipped". Clipping causes a minor increase in the wheel's flow capability; however, it dramatically lowers the turbo efficiency. This reduction in efficiency causes the turbo to come up on boost at a later engine speed (ex. increased turbo lag). High performance applications should never use a clipped turbine wheel. All Garrett GT turbos use modern unclipped turbine wheels.
 
  Corrected Air Flow   
 
When plotting actual airflow data on a compressor map, the flow must be corrected to account for different atmospheric conditions that affect air density.
Example:
Air Temperature (Air Temp) - 60°F
Barometric Pressure (Baro) - 14.7 psi
Engine air consumption (Actual Flow) = 50 lb/min
Corrected Flow= Actual Flow SQR([Air Temp+460]/545)/ Baro/13.95
Corrected Flow= 50*SQR([60+460]/545)/ 14.7/13.95 = 46.3 lb/min
 
  Efficiency Contours   
 
The efficiency contours depict the regional efficiency of the compressor stage. When sizing a turbo, it is important to maintain the proposed lug-line with a high efficiency range on the map.
 
  Free-Float   
 
A free-floating turbocharger has no Waste-gates device. This turbocharger can't control its own boost levels. For performance applications, the user normally must install an external Waste-gates.
 
  GT 
 
The GT designation refers to Garrett's state-of-the-art turbocharger line. GT-series turbos use redesigned bearing systems and modern compressor/turbine aerodynamics. These new compressor and turbine wheels represent huge efficiency improvements over the old T2, T3, T3/T4, T04 products. The net result is increased durability, higher boost, and more engine power over the older T-series product line.
 
  On-Center Turbine Housings   
 
On-center turbine housings refer to an outdated style of turbine housing with a centered turbine inlet pad. The inlet pad is centered on the turbo's axis of rotation instead of being tangentially located. Using an on-center housing will significantly lower the turbine's efficiency. This results in increased turbo lag, more back-pressure, lower engine volumetric efficiency, and less overall engine power. No Garrett OEM's use on-center housings.
 
  Pressure Ratio   
 
Ratio of absolute outlet pressure divided by absolute inlet pressure
Example:
Intake manifold pressure (Boost) = 12 psi
Pressure drop, inter-cooler (DPIntercooler) = 2 psi
Pressure drop, air filter (DPAir Filter) = 0.5 psi
Atmosphere (Atmos) = 14.7 psi at sea level
PR = (Boost + DPIntercooler+ Atmos) / (Atmos-DPAir Filter)
PR = (12 + 2 + 14.7) / (14.7 -.5) = 2.02
 
  Surge Line   
 
The surge region, located on the left-hand side of the compressor map, is an area of flow instability typically caused by compressor inducer stall. The turbo should be sized so that the engine does not operate in the surge range. When turbochargers operate in surge for long periods of time, bearing failures may occur.
 
  Trim  
 
Trim is an area ratio used to describe both turbine and compressor wheels. Trim is calculated using the inducer and exducer diameters.
Example:
Inducer diameter = 88mm
Exducer diameter = 117.5mm
Trim = Inducer2/Exducer2
Trim = 882/117.52 = 56 Trim
As trim is increased, the wheel can support more air/gas flow.
 
  Waste-gates   
 
A Waste-gated turbocharger includes an integral device to limit turbo boost. This consists of a pneumatic actuator connected to a valve assembly mounted inside the turbine housing. By connecting the pneumatic actuator to boost pressure, the turbo is able to limit its maximum boost output. The net result is increased durability, quicker time to boost, and adjustability of boost.
 
  

Injectors and Fuel System

In order to make your Mega Squirt work on a vehicle, you will need the following additional fuel system items to suit your installation:

  • injectors and bungs/manifold,
  • throttle body,
  • high pressure fuel pump, supply/return lines, and rails,
  • and a fuel pressure regulator.

Note that if you start by installing Mega Squirt with a throttle body injection unit from a late model vehicle, it will likely come with the injectors, pressure regulator, and throttle position sensor; this will greatly simplify the installation of Mega Squirt on a vehicle that was previously carbureted. If you choose a TBI unit, you will not need as much wiring, fuel rails, manifold modifications for injector bungs, etc. Once you get the TBI set-up working, you can later switch to port injection and use the TBI as an air door only.

Injector Selection

In order to properly install your Mega Squirt, you need to select and install fuel system components appropriate for your engine. Most important is that you have fuel injectors that are the correct size in terms of flow rating. In fact, most injectors are a similar size physically, though there tends to be more variation in throttle body injection injectors than in port injectors. Typical dimensions for a port injector are:

The manifold injector bungs are 0.530"-0.535" inside diameter [about 17/32" or 13.5 mm]. The fuel supply rail bungs for the top of the injectors are the same size.

Here are two TBI injectors. One the left is a Holley 85 lb/hr TBI injectors (apparently similar to some Chrysler TBI injectors), on the right is a GM TBI injector from a 1984 Corvette:

Injectors that have too large a flow rating will make it difficult to tune the engine at idle and cruise. Injectors that have too small a flow rating can starve the engine of fuel at full power, and seriously damage your engine. To determine how big your injector's flow rating should be, multiply estimated horsepower (HP) of your engine by the brake specific fuel consumption (BSFC)* and divide by the number of injectors and the desired duty cycle and you will get a rough estimate of injector size:

Injector-Size = (Horse Power * BSFC) / (#Injectors * Duty Cycle)

for example, a 135 horsepower gasoline fueled 4 cylinder engine with 2 throttle body injectors and 0.55 brake specific fuel consumption gives:

(135 HP * 0.55 lb/hr/HP) / (2*.85) = ~ 43.7 lb/hr

Injectors rated between 42 and 45 lb/hr would be okay in this case.

*BSFC is the amount of fuel your engine uses to make 1 horsepower for one hour. It is usually between 0.42 and 0.58 at wide open throttle. Normally aspirated engines with efficient combustion processes are at the lower end of the BSFC scale [~0.45], supercharged engines tend to be towards the higher end [~0.55].

 

Or you can use the following chart to select injectors based on the total horsepower of your engine and the total number of injectors:

Injectors Rating Required for Specified Horsepower
in lbs/hr and (cc/min)

Number of Injectors

Horsepower

1

2

4

5

6

8

100

59 (620)

29 (305)

15 (158)

12 (126)

10 (105)

-

150

88 (924)

44 (462)

22 (231)

18 (189)

15 (158)

11 (116)

200

-

59 (620)

29 (305)

24 (252)

20 (210)

15 (158)

250

-

74 (777)

37 (389)

29 (305)

25 (263)

18 (189)

300

-

88 (924)

44 (462)

35 (368)

29 (305)

22 (231)

350

-

-

51 (534)

41 (431)

34 (357)

26 (273)

400

-

-

59 (620)

47 (494)

39 (410)

29 (305)

450

-

-

66 (693)

53 (557)

44 (462)

33 (347)

500

-

-

74 (777)

59 (620)

49 (515)

37 (389)

550

-

-

81 (851)

65 (683)

54 (567)

40 (420)

600

-

-

88 (924)

71 (746)

59 (620)

44 (462)

based on 0.50 BSFC and 85% duty cycle
Turbo/supercharged engines should add 10% to listed minimum injector size

Injectors are usually rated in either lbs/hour cc/min. The accepted conversion factor between these depends somewhat on fuel density, which changes with formulation (i.e., by season), but the generally used conversion for gasoline is:

1 lb/hr ~ 10.5 cc/min

 

 

 

Another way to select injectors is to take them from an engine that makes nearly the same power as your engine will [assuming the same number of injectors].

If your regulator is adjustable (many aftermarket ones are), you can also adjust the fuel pressure to achieve different flow rates. The formula is:

new flow rate = old flow rate × SQRT[new pressure÷old pressure])

So for example, if you had 30 lb/hr injectors rated at 43.5 psi, and you went to 50 psi, you would get:

flow rate = 30 * SQRT(50/43.5) = 32 lb/hr

 

 

Do not run more than 70 psi fuel pressure, or the injectors may not open/close properly.

However, do not install injectors with a much larger flow capacity than you need. Very large injectors will create idle pulse width issues that will make tuning very difficult. You can estimate your idle pulse width beforehand. For proper tuning, you will need an idle pulse width of at least 1.7 milliseconds. To calculate the idle pulse width, recall that the fueling equation for Mega Squirt is:

PW = REQ_FUEL * VE * MAP * E + accel + Injector_open_time

So, find the REQ_FUEL that corresponds to your injector's flow rate and engine size. There is a REQ_FUEL calculator in Mega Tune, and also here. If you have the engine running , you can check the MAP at idle (or you can guess - pick about ~25 kPa for a stock cam, ~35 kPa for a performance cam, ~45 kPa for a race cam). Then you only need the idle VE (and injector open time) to predict the idle pulse width, since this is minimum when there are no enrichments (E=0, accel=0). Note that you need to use the 'downloaded' REQ_FUEL, which is adjusted for the number of injectors and their staging.

A good "rule of thumb" for idle VE is 30%. You may actually be 20% or 40% depending on things like compression, overlap, ignition timing, etc., but 30% will be close enough to give you a good idea about idle pulse width. And use 1.0 msec for the injector opening time, unless you have a very good reason to do otherwise.

For example, on one engine:

PW = 6.3 msec * 30% * (33 kPa / 100 kPa) + 1.0 msec = 1.62 msec

And the measured idle PW was 1.7 msec. So these injectors are okay on this engine, but just barely. If it had been 1.2 or 1.3 milliseconds, these injectors would have presented very significant tuning problems on this engine.

Injectors frequently have identifying numbers stamped on them. You may be able to identify your injectors by looking on:

http://www.geocities.com/MotorCity/Pit/9975/dataBySubject/Injectors.html
or
http://www.telusplanet.net/%7Echichm/tech/injectors.pdf

Injectors should not be used at more than 80-85% duty cycle. However, injector rates are always specified at 100% duty cycle and some nominal pressure (usually 43.5 psi = 3 atmospheres). The manufacturer leaves it up to you to determine a system pressure and maximum duty cycle in order to compute the resulting flow.

Injectors are driven by an electrical signal from Mega Squirt that grounds the +12 volt supply through the injectors to open them. Once they are open, they flow at a constant rate until closing. The amount of time required to open and close the injectors is specified in Mega Squirt as the 'Injector Opening Time' (usually about 1.0 msec). Here is an example of a low impedance injector's pulse voltage, current, and fuel flow:

Pulse Width Modulation

Injectors are either high impedance or low impedance. High impedance injectors (usually about 12-16 ohms) can take a 12 supply directly, without a form of current control. Low impedance injectors (generally below 3 ohms) require some form of current limiting. With Mega Squirt, you can use resistors to limit current, or you can use Pulse Width Modulation (PWM), which is a software solution built in to Mega Squirt.

PWM works by switching the 12 volt ground to the injector on and off very rapidly (in about 0.000059 seconds!). The ratio of the "on" time to the "off" time determines the current through the injectors. However, the easiest way to think of the PWM% is as a percentage of the supply voltage, so 50% PWM on a 14 volt supply becomes effectively 7 volts on average, 28% would be 4 volts, etc.

Remember that pulse width and PWM% are two different things. Pulse width is the total duration of the signal whereas PWM% is the ratio of 'on-time' to 'off-time' within the pulse. So in the above illustration, the pulse width for both is the same, but the PWM% for the first is 50%, while for the second it is 25%.

The PWM% you will be able to use depends on the fly back circuit you have. Version 2.2 hardware generally requires about 55% to 75% PWM. Often the engine will run with lower values, but will not have enough voltage to re-start. Note that using embedded code version 2.986 or higher will disable PWM during cranking, allowing somewhat lower PWM% values. The Fly Back Board allows you to lower the PWM% dramatically, generally to 30% or less. It also helps close the injectors faster.

With better fly back control, you can reduce injector opening times (recall that the injector opening time is really the sum of the opening and closing times), and increase the duration of the 'controllable' part of the pulse width (i.e. after the opening time),

The important thing about the injector open time is that it sets a lower bound for the pulse width (regardless of whether PWM is on, etc.). so if you have injector opening at 1.7ms, you cannot set it to 1.6 or anything lower, even with VE=0. Mega Squirt assumes no fuel is injected during this time, but some is, though it is hard to calculate how much. The longer it takes to open, the more fuel is likely injected during opening. With lower opening times (by allowing full voltage (i.e. no PWM), you can get the injectors open quicker.

Your engine will need a certain amount of fuel to run correctly at idle when fully warmed up. If this amount is below that injected during the injector opening time, you will always be rich and have no way to lean it out, short of reducing the fuel pressure.

Note that PWM is disabled (in v2.986 code) during cranking so the injectors get full battery voltage. This makes 'severe' starting conditions (lower cranking voltages, etc.) less likely to result in the injectors not opening. This is not possible with resistors, unless you devise a way to bypass them during starting (like the older cars did for the ignition coil).

When using low-impedance injectors, which are also called peak and hold injectors (P&H), you wire them in parallel. The wiring is the same for P&H or saturated [high-impedance].

To exceed the recommended number of injectors (see below) either requires resistors in series with each injector or a modified fly back setup.

The following is a guide as to whether you need to use resistors or the fly back board:

Injector DC Resistance
Number of Injectors
(total)
Mega Squirt
Hardware

PWM Mode

High (12 - 16 ohm)

up to 12

V2.2

no PWM current limit

Low (> 2.4 ohm)

up to 4

V2.2

use PWM current limit

Low (> 2.4 ohm)

more than 4

V2.2

Use injector resistors
or
fly back board

Low (< 2.4 and > 1.2 ohm)

more than 3

V2.2

Use injector resistors
or
fly back board

Low (< 1.2 ohm)

up to 2

V2.2

use PWM current limit

Low (< 1.2 ohm)

more than 2

V2.2

Use injector resistors
or
fly back board

One sure way to know if you can't use the standard V2.2 fly back circuit is to have a fly back failure. The circuit will most often fail after some time spend at high speeds and loads, rather than immediately when you start the engine for the first time. Generally, when the fly back circuit fails, the Mega Squirt works okay on the stim, but not on the car.

Signs of an impending fly back failure are:

When the fly back fails, sometimes Q1 (the TIP32 on the bottom of the PCB) looks pretty rough, all burnt, etc. However sometimes it looks fine.

If Q1 (on the bottom of the board) does look burnt however, this is a sure sign of a fly back failure.

To repair after a fly back board, you need to adopt the fly back board, or use injector resistors.

To use the fly back board, you will discard many of the original V2.2 fly back components, so don't replace anything until you install the fly back board.

However, if you are going to repair the V2.2 fly back circuit and use injector resistors, you need to replace a number of components:

  • Q1 - 497-2629-5-ND, ~98¢,
  • U7, the 34151 FET driver IC - IXDI404PI-ND, ~$4.12,
  • Q2 and Q7, the FETs - IRFIZ34G-ND × 2 for ~$1.43 each.
If you are doing repairs, you might also get a socket for the FET driver AE7208-ND (~35¢), it ensures the FET driver sees no heat during assembly, and makes it easier to replace in the future.

The resistors and diodes of the V2.2 fly back circuit seem to survive the fly back failure generally, though you could order and replace them to be sure (they are reasonably cheap).

They are:

  • R12 and R17 - 22QBK-ND, ~28¢ for 5,
  • R32 - 270H-ND, ~27¢ for 5,
  • D20, D22, and D23 - 1N4001DICT-ND ~26¢ each,
  • D21 - 1N4753ADICT-ND, ~36¢ each.

In order to prevent future flyback failures, you can adapt either the flyback board or injector resistors.

The flyback board:

  • allows the injectors to open somewhat faster than resistors will, improve the dynamic range of the injectors (resistors added about 1.0 millisecond to the injector opening time),
  • the flyback board gives the injectors 'full power' while cranking, potentially making for better starting when it is very cold or when your battery is marginal,
  • the flyback board potentially allows you to minimize the current through the injectors by tuning, theoretically helping them to last longer due to lowered heating of the injector coils,
  • the flyback board and components are cheaper in some cases than resistors, if bought new, depending on how many you have to use.

However, resistors are:

  • simpler,
  • have no active components to fail,
  • require little additional wiring, and
  • have been proven in millions of mid-eighties OEM applications.

For example, the injector resistors 825F7R5-ND are $4.66 each. The flyback board ($12) and components ($6.86) total $18.86, so the 'cross-over' point is 4 injectors, using new components (depending on shipping, etc.). Of course, if you source your resistor pack from a scrap yard, or if your vehicle already has them, this is cheaper!

The Fly back Board

People running a number of very low impedance injectors have reported problems with the flyback circuit failing. Typically, this will happen with 4 or more low-impedance injectors, such as the Holley 85 lb/hr TBI injectors. This can be avoided by using resistors in series with the injectors, and disabling the pulse width modulation (PWM). However, a more elegant solution that continues to use PWM is the Fly back Board.

The Fly back board is an additional 'daughter card' for Mega Squirt that does a number of things:

  • It provides each injector bank with a separate flyback circuit,
  • It uses 'heavy-duty' components capable of handling higher currents and transients,
  • It has a very substantial aluminum heat-sink,
  • It invokes the flyback circuits only after the PWM has ended, eliminating the load on the flyback components during PWM.

The Fly back Board installs in the up half of the Mega Squirt case. It slides into the lowest slot, and is attached to a substantial heat sink (that you make yourself from ½"x¾" aluminum angle). Six 20 to 22 gauge wires (two injector banks, two CPU [X0, X1], +12 volts, and ground) connect the Flyback Board to Mega Squirt.

The Flyback board must be used in conjunction with embedded code version 2.986 or higher. This code has the proper switching code to turn the Flyback circuits on after PWM ends.

This is the schematic for the Fly Back board:

Like all other Mega Squirt kits, you order the PCB at:

http://www.bgsoflex.com/mspo1.html

then place an order with Digi-Key through the BOM at:

http://www.megamanual.com/fbbom.htm

for most of the remaining parts.

To assemble the flyback board, follow these instructions:

1) Disable the existing flyback circuit. You can do this by cutting the leads to D22 and D23. You can remove the remaining flyback components if you wish. They are: R32 (270 ohms, ½ watt resistor), Q1 (TIP42 transistor), and D21 (36 volt Zener diode). Removing components is easiest if you cut the leads, then remove each lead separately. This puts less heat into the board and other components.

2) If you are upgrading your flyback components because of a flyback failure, replace the 34151 FET driver IC, and the two FETs (IFRIZ34) as well.

3) Install and solder R101, R102, R103, R105, R106, and R107. All of these are 270 ohm, ½ watt resistors {270H-ND}.

4) Install and solder R104 and R108 {1.0 Kohm, ¼ watt}.

5) Install and solder D100 and D103 {fast recovery diodes, FR302DICT-ND}. Be sure to orient them with the banded end as shown on the silk screen.

6) Install and solder Q103 and Q106 {transistors, PN2222AD26ZCT-ND}. Note that the flat side faces to the left when the silk screen printing is oriented so that you can read it. You have to bend the middle leg slightly towards the flat side to fit it in the holes.

7) Install and solder D102 and D104 {36 volt Zener diodes, 1N4753ADICT-ND}. Be sure to orient them with the banded end as shown on the silk screen.

8) Before installing the four T0-220 transistors, you need to fabricate the heat-sink. You need two 3½" (89mm) long pieces of aluminum angle that are ½" by ¾" (13mm x 19mm), about .040" to .080" thick (1.0mm to 2.0mm). Drill (1/8" - 3mm) these as indicated below:

Make sure your heat sink is no longer than 3½" (89mm), so that it can sit flat against the case. The edge of the heat sink is flush with the end of the case. Drill corresponding holes in the case. Be sure to drill the correct end of the case (the DB9/LED end). Verify that the heat sink will sit flat when bolted to the case.

The heat sink is design to attach to the FlyBack board by the four transistor mounting holes. The heat sink should just be tall enough to allow the FlyBack board to slide underneath it when it is installed in the lowest slot of the upper case. Make sure to get the heat sink dimensions correct - otherwise you could stress the FlyBack board and/or impair the heat conduction abilities of the FlyBack board. Either could lead to failure.

9) Assemble the heat sink (but do not fasten it to the case) as shown below using ½" (13mm) #4-40 machine screws and nuts:

10) Bends the leads of the TIP125 Darlington transistors Q102 and Q105 so that the mounting holes and leads line up with both the PCB and heat-sink. Make sure the leads of the transistor will not touch the heat sink! The heat sink is sandwiched between the transistor body and the PCB.

Apply heat sink compound between the two angles, and also between the transistors, mica, and heat sink. Bolt the transistors in place using #4-40 machine screws and nuts using a mica insulator kit between each transistor and heat sink. Be sure to place the bolts for the transistors/heat sink through the bottom, and the nuts on the top, as clearance is limited.

You might have to trim the mica with a sharp pair of scissors to make it fit properly. Solder the transistor leads in place.

Use a multi-meter on its highest resistance setting to check that you have "infinite" resistance between the metal mounting tab of the transistor body and the heat sink. If this is not the case, your insulator is not insulating. Find out why. You may have to de-burr the transistor mounting holes in the heat sink (you can counter sink them with a quick touch of a ¼" drill). You can also sand the surface of the heat sink lightly where the transistors bolt on. Be sure to thoroughly clean the heat sink afterwards.

Do not proceed until you have electrically isolated the TIP125 transistor mounting tab from the heat sink.

11) Bends the leads of the TIP32C {TIP32CFS-ND} transistors Q101 and Q104 so that the mounting holes and leads line up with both the PCB and heat-sink. Make sure the leads of the transistor will not touch the heat sink!

Apply heat sink compound between the two angles, and also between the transistors and heat sink. Bolt the transistors in place using #4-40 machine screws and nuts. These transistors do not need a mica insulator. Be sure to place the bolts for the transistors/heat sink through the bottom, and the nuts on the top, as clearance is limited. Solder the leads in place.

12) Run a 20 to 22 gauge jumper wire from X0 on the Mega Squirt PCB (near the CPU) to X0 on the Flyback PCB.

13) Run a 20 to 22 gauge jumper wire from X1 on the Mega Squirt PCB (near the CPU) to X1 on the Flyback PCB.

14) Run a 20 to 22 gauge jumper 12 volt power wire from the unmarked through hole just to the right of X13 (and slightly below) on the Mega Squirt PCB to the hole marked 12V on the right side of the FlyBack PCB.

15) Run a 20 to 22 gauge jumper ground wire from the unmarked through any of the holes for the 'non-banded' end of the unused diodes (at D1, D2, D3, or D4) on the Mega Squirt PCB to the hole marked GND on the right side of the FlyBack PCB. For example, if you use D4, install the ground wire from the end of D4 closest the CPU to the hole marked GND on the FlyBack PCB.

16 a.) Connect a 20 to 22 gauge wire from the hole at the non-banded end of D22 (the one you removed) on the Mega Squirt PCB to the hole on the Flyback PCB marked INJ1.

16 b.) Connect a 20 to 22 gauge wire from the hole at the non-banded end of D23 (the one you removed) on the Mega Squirt PCB to the hole on the Flyback PCB marked INJ2.

17) Install the heat sink and FlyBack board into the case. The board slides in the first slot in the case. Apply heat sink compound between the case and heat sink. Use #4-40 screws to fasten the heat sink. You may need to bend any of C12, C15, C17, C18, C19, C22, C23, and/or C24 over a bit to get enough clearance, depending on how much lead length you left when they were originally soldered in.

18) Make sure to load version 2.98 embedded code or higher into your Mega Squirt.

19) Reset your PWM parameters. Try 30% and 1.0ms to start, then "tune" them as described in the manual.

20) Reassemble your case, and you are ready to go! Be careful not to 'pinch' any of the connecting wires between the two halves of the case when you reassemble.

Note, if you assemble your flyback board, but find that it won't allow your engine to run with less than ~75% PWM, the flyback board is NOT working. You need to find out why. You can:

  1. Go over the manual again, and verify the each component and it's orientation, if applicable,
  2. Check all the soldered joints and connections,
  3. Verify that the board is getting a good ground,
  4. Verify that the board has 12 volts,
  5. Verify the signals at the X0, X1, INJ1, and INJ2 connections (with an LED tester and the Mega Squirt on a stim),
  6. Verify that there is 'infinite' resistance between the TIP125s and the heat sink,
  7. Verify that the connections are to the correct place on the boards (both flyback and Mega Squirt),
  8. Verify that you have V2.98+ embedded code (reload if necessary).

If it passes all those tests, you have to start looking at individual components. Often, the flyback board is installed because of a failure, in which case the FETs and FET driver should probably be replaced as well.

Injector Resistors

However, instead of the flyback board, you may choose to use resistors in series with your injectors.

Several people reported that resistors do NOT result in significantly longer opening times, or any other troublesome effects, so this is a good solution for many installs. To eliminate PWM altogether, use a 5 to 8 ohm resistor (with a 20 to 25 watt rating) in series with each injector.

If you want to avoid using PWM with your low-impedance injectors, you can use ballast resistors in series with the injectors. You should use one resistor (20-25 Watts) in series with each injector, otherwise the injectors may not all draw the same current, and the failure modes become complicated and difficult to diagnose. As well, you would need a very large resistor to handle more injectors. For example, if you allowed 2 Amps through four 1.2 Ohm injectors wired in parallel (0.3 Ohms total) to one 7 Ohm resistor, the power dissipated would be:

P = V * I = 12.5 Volts * 2 amps x 4 injectors = 100 Watts!

If you use resistors that limit injector current to less than 2 amps, you can disable the PWM mode (by setting PWM% to 100%, and time threshold to 25.4msec) and treavolts Requiredt the system as high-impedance. To limit the current to under 2 amps, you need:

resistor ohms = (alternator voltage / 2.0 amps) - injector resistance

For example:

resistor ohms = (14.0 volts / 2.0 amps) - 1.2 ohms

=> resistor ohms = 7.0 - 1.2 = 5.8 ohms

You can also use the calculator below. Enter your injector resistance in ohms, your hold current in amps, as well as your injector impedance in ohms, in the form below and press the "Compute resistor" button.

Injector resistance (ohms)
Hold current (amps)
usually ~1 or 2 amps
Supply voltage (volts)
usually ~14 volts
Required Resistors (ohms)

The 25-watt resistors aluminum case Ohmite resistors (with 1% tolerance) from www.digi-key work well. Below is a picture of a 7.5 ohm resistor, Digi-Key part number 825F7R5-ND.

Ohmite has several suitable resistors, with part numbers that start 825F (25 Watt, aluminum case with mounting ears) and end in XRY, where X and Y indicate X.Y ohms. Depending on injector, pick 2-8 ohms or so.

You may be able to use less resistance to protect the flyback components - just a few ohms combined with PWM may do the trick. Be sure to use one resistor in series with each injector, and then you can parallel these into the two banks. Do not share two or more injectors per resistor, use a resistor per injector.

There a lower bound to the pulse width, below which a low impedance injector cannot be expected to reliably function. There are two problems with running the very lower pulse widths that result from large injectors. There is a limit on the physical ability of the injector to opening and close as quickly as possible, and there is also a limit to the ability of the Mega Squirt controller to adjust the pulse width to an optimum value at very low pulse widths.

The absolute physical limit depends on your particular injectors and the hardware that controls them. Some are able to go as low as 1.1 to 1.5 milliseconds [ms]. Note that there are three components to the injection duration - the opening time, the commanded pulse, and the closing time. Ideally you would want the opening and closing times to be a short as possible to have the controller determining as much of the amount of the time injected as possible. The opening time is difficult to adjust given a certain operating voltage. The closing time, however is controlled to a degree by the flyback circuit in the Mega Squirt.

With very large injectors [for a given application], the idle pulse widths may be around 1.0 millisecond. This is a problem because in the standard code for Mega Squirt, the resolution of the steps is 0.1 ms. So a 1.1 millisecond “squirt” will only be able to be adjusted in ~9% increments (i.e. 1.0, 1.1, 1.2 etc.), which may be too coarse to get a good idle. The high-resolution Mega Squirt code can help in this situation, but you lose the PWM current limiting mode so you have to run resistor packs with peak and hold low-impedance injectors.

An ideal idle duration is around 2.3 ms, and this is approximately where properly sized injectors should operate. This gives good resolution [~4%], and you should be able to get a real good idle.

You will need to acquire connectors for wiring the Mega Squirt to your injectors, etc. Niehoff has individual injector connectors under part number 28419 (connector) and 28418 (sealing boot). On the web, Waytek has lots of different connectors that you can use in building your Mega Squirt. Their prices are about as cheap as you can find. The injector connectors are AMP part number 827551-3, but sometimes you have to buy a large quantity. Also try DelCity. They are not quite as cheap, but they may have stuff you cannot get from Waytek.

Injector Bungs

You can get information on injector bungs for port injectors by checking out www.sdsefi.com for injector/manifold installation information, along with lots of other great information. The bungs are 0.530"-0.535" inside diameter [about 17/32" or 13.5 mm]. The fuel supply lines for the top of the injectors are the same size.

VERY IMPORTANT! If you do not own at least two fire extinguishers, go buy some right now! Experimentation with EFI can be very dangerous because you are playing with high pressure gasoline. Install at least one fire extinguisher in your work area (away from where the fire is mostly likely to occur) and carry another one in your car. Do not ignore this advice. We do not want to be visiting you in the hospital or worse!

MSD and others have an “Epoxy-In Pocket” fuel injector bung as PN 2120 (set of 8). Holley also offers them as PN 534-83 for a four pack (~$50), 534-84 for a pack of six (~$72), or 534-85 for a pack of eight (~$94).

These bungs can be held in place with epoxy or welded and is used for fixed fuel rail systems only. These bungs are CNC-machined from aluminum for precise dimensions and have a ¾” OD. Internally, the pockets are contoured to accept the bottom sealing O-ring of a standard injector. MSD also has “Thread-In Pockets”. The aluminum pockets will screw into a ¾”–16 hole and are supplied with a #8 O-ring to seal the pocket to the manifold. PN 2125 gets a set of 8.

Fuel Rails

Most injector systems will use one or more fuel rails. These serve two functions: they supply fuel to a multiple number of injectors (4 on a 4 cylinder, for example), and they physically locate the tops of the injectors. Most OEM rails can be made to work with standard engine configurations, but if you are doing a custom conversion you may have to fabricate fuel rails. Many place supply blank aluminum fuel rail extrusions in whatever length you need. One example is Ross Machine. They have two styles of fuel rail extrusion. They can also create custom fuel rails for you, with the injector holes placed to suit you.

The aluminum extrusion comes in two sizes:

  • Dash 10 (.800" Bore) - $10/foot, and
  • Dash 6 (.500" Bore) - $12/foot.

For fabricating fuel rails, MSD has “Fuel Delivery Top Mounts”, PN 2115, set of 8. These fuel delivery mounts are CNC machined from #304 stainless steel for great durability and precise dimensions. They slide over ½” steel tubing (MSD PN 2205) then are brazed or TIG welded in place to form a fuel rail. Fuel is routed through a 5/16” hole aligned to the mount and the injector. The PN 2105 Fuel Rail Clip is required for assembly. Their “Stainless Steel Fuel Tubing”, PN 2205, comes in 2 four feet lengths of 304 stainless steel tubing, and is perfect for making custom fixed rails. The seamless tubing has a ½” OD and .035” wall.

Throttle Bodies

Your throttle body choice depends on whether you are going to use throttle body injection or port injection.

Your throttle body needs to do 2 things:

  1. control the amount of air going into the engine, and
  2. report the throttle position to Mega Squirt via a TPS.

For port injection, you can convert an existing carb, to do both jobs - the carb already controls the air flow, you have to adapt a TPS sensor to it. You may choose to machine out the venturis, remove the float bowls and fuel circuits if you wish, but that isn't necessary (but may be desirable for a number of reasons, including increased power!).

Some people use the complete individual runner (IR) throttle body and injector set-ups off late model motorcycles - they often have enough flow for automotive engines, and are frequently available cheaply on eBay.

However, if you are planning on a throttle body injection set-up, you need a dedicated TBI unit (in order to supply the fuel to the injectors, etc.), which can be hard to find for larger engines - Holley has made a 4bbl TBI for years (in 650, 700 and 900 cfm sizes), and as the computer fails regularly on these, they are sometimes available separately on eBay. TBIs have the advantage of having the fuel pressure regulator built in, of course.

Note that for either port or throttle body injection you can use multiple throttle bodies to support your power levels, if your manifold configuration can be adapted for them.

However, if you are uncertain of your throttle body's application, you can measure the throttle bore size. However, you can't really compare the throttle of an EFI throttle body to the throttles of a carb. This is because the throttle(s) of a EFI TB is the main restriction, but on a carb, it is the venturis that are the main restriction. So you really have to compare the EFI throttle size to the carb's venturi size. However there are also a number of other considerations, such as that you can go larger with a EFI TB than a carb without suffering so many adverse effects because a vacuum signal isn't needed for the EFI to operate.Fuel delivery is always good with EFI (well, mostly). When selecting a throttle body, there are a number of considerations. You need it to flow enough to support your engine's horsepower (or more correctly, to not restrict your engines power). Generally, you want to take the throttle body from an engine that made similar horsepower to your engine.

However, there are some drawbacks to a too large throttle body:

  • At low rpm, you go from low kPa to 100kPa with very little throttle movement, making driveability 'worse'. For example, with a very large throttle body you may get 100 kPa at 20% throttle at 2000 rpm. This means if you want to hold it at 40 kPa for cruise, I have to be very steady on the throttle, as small movements may produce large changes in engine output (so it's harder to be smooth), and
  • A small throttle movement (and a small V/sec TPS signal change) can result in a very large change in MAP (as mentioned above) at low rpms. The result is little (or no) accel enrich when the engine needs it most. However, you can usually tune around circumstances like this by richening the VE table at low rpms and higher kPa (say < 2500 rpm and> 70 kPa) by about 5-7%. This has a negligible affect on fuel economy, since you likely never see 70 kPa while cruising.

For reference, the GM tuned Port Injection engines used throttle bodies with two 48mm throttles. These support about 230 horsepower, however these throttles were not the limiting factor in the power produced by these engines.

To calculate how much horsepower you can make from a given throttle body size, you can use the estimator below:

 

Note that the above is for naturally aspirated engines having a common plenum - individual runner manifolds will need larger throttle bodies, turbocharged 'blow-through' engines can get by with somewhat smaller throttle bodies

Fuel Supply System

In order to use Mega Squirt, you will have to implement a high-pressure fuel supply system. You MUST understand how to do this properly, and this manual DOES NOT include everything you need to know. If you are unsure about your installation, have a qualified mechanic look it over before attempting to start your vehicle.

Fuel Pumps

You will need a high pressure pump with enough volume at your operating pressure to feed you engine under maximum load. Typical pressures needed in the neighborhood of ~45 psi for port fuel injection, ~10-20 psi for TBI injection. A port injection pump will work with TBI, but not vice-versa.

OEMs usually place pump inside the fuel tank. In an EFI retrofit it is generally easier to use an external fuel pump. Ford used external fuel pumps on 1989 era 150 trucks which may be a candidate for use. These are high pressure [port EFI] pumps that will work in most applications. Econoline vans have these as well.

The external pumps used in Ford F150 fuel injected trucks from the 89-93 model years are Delco EP286. At 12 volts, the operating pressure is 70-95 PSI with 36-40 gals per hour. The biggest Delco pump is the EP424, which is 75-90 PSI at 40 gals per hour. EP 268 is a GM# 25117086, EP 424 is a GM# 25176156."

Here is a picture of the Econoline pump:

The Carter pump #P70199 (the outlet is 7/16 standard pipe thread and the inlet is 15/32 clamped hose type fitting or 3/4 standard thread. The specs are 95-PSI max, 68-93 G/Hr wide open). This is the highest flowing Carter external fuel pump in the book. It will produce up to 95 psi, and crosses over to EP7107 at Kragen for about $80 (unfortunately one end does not come off like the Carter). You might want the Ford style pump EP7109($80). You will need this if you want to be able to modify ends to be 3/8".

Others have had luck using the external pump from various fuel injected VolksWagen models (87 VW Fox, for example). Part number is: Bosch 0 580 254 957 reportedly rated at 90 GPH@ 70PSI, you might find them for about $130 new from www.germanautoparts.com. This pump consists of a fuel pump, filter, and an "accumulator". You can leave the accumulator in place since it does not affect the running volume or pressure, and on used pumps they are often rusted so you might not want to mess with it.

Auto Performance Engineering has many high volume Walbro pumps (and their specifications) on their site.

Fuel Line

Steel tubing is recommended, but you MUST have short sections of rubber line in the feed and return lines between the engine and frame to allow for engine movement. The return line should have minimal restriction. For reference, GM systems typically have 3/8" feed lines and 5/16" return lines.

You may be able to use your original fuel line as a return line, plumbing a new 3/8" (10mm) line for fuel supply. You can run the return line into the tank, or reroute it to a fitting or nipple you install in the fuel tank filler neck/tube assembly (in which case you may be able to use the original pick-up for your supply line). If you run a new pick-up into the tank, it will need a filter. GM sells a sock-type filter that is a good fit for 3/8" lines. It is part number 5651702 and costs about $15.

You may have to fabricate fuel lines for your system. Tubing is available in steel, stainless steel, and aluminum for this purpose. The size is generally given as the outside diameter of the tubing. Unless you have a very unusual combination (or very high horsepower, well over 500+), you should be able to use 3/8" tubing for both the supply and return lines.

Buy a good tubing bender (there are numerous styles in various price ranges) so that you don't kink or collapse the tubing while bending it. (You can also bend it over a V-belt pulley, in some cases.)

The AN (Army-Navy) 'dash' system of hose and fitting sizing was established many years ago by the American military as a common measurement for hoses and fittings. It designates the outside diameter of the metal tube that is compatible with each size of fitting. The AN dash measure is the standard for performance hose applications. These dash sizes are expressed in 16th of an inch. For example, an -06 fitting is 6/16 of an inch or 3/8", just right for our fuel lines!

Most fittings and adapters in the automotive aftermarket are based on a 37° sealing angle (SAE J514 37° - formerly known as JIC). These are also often referred to simply as AN fittings. Male and female 37° fittings will mate together for a leak-proof connection.

SAE J514 (37° AN)
Dash Size Inch Size Nominal Thread Size
04 1/4 7/16-20
05 5/16 1/2-20
06 3/8 9/16-18
08 1/2 3/4-16
10 5/8 7/8-14

Be aware that there are other similar fittings and adapters that use a 45° sealing surface (SAE J512), such as those commonly available at your local hardware store for flared copper pipe. These 45° fittings and adapters can also be found in some OEM automotive applications. However, although they may look very similar to a 37° fitting, they are not interchangeable. In some sizes, they may thread together (-02, -03, -04, -05, -08, -10), but will not seal properly, due to the difference in sealing surface angles. Be sure you know the sealing angle of the fittings you are connecting!

SAE J512 (45°)
Dash Size Inch Size Nominal Thread Size
04 1/4 7/16-20
05 5/16 1/2-20
06 3/8 5/8-18
08 1/2 3/4-16
10 5/8 7/8-14

Abrasion (the rubbing of the hose against some other component) is the number one cause of hose failure. A leaking fuel hose can start a very dangerous fire in your car, so make sure hose assemblies are routed properly to reduce the chance of any abrasion damage. Use a support every 12 to 18 inches (30 to 45 cm) to secure the hose. For chafe protection, be sure to install a grommet at any point a hose passes through a panel or bulkhead.

Besides steel or aluminum tubing fuel line, you can also use one of the steel or nylon braided hoses from various suppliers. Generally these use the same AN 'dash' sizing system, and can use appropriate fittings to connect to 37° flare, NPT thread, or other systems.

Note that if you are using a factory fuel rail, you may be able to find an aftermarket adapter to mate your OEM fuel fitting to an AN hose. For example, Accel offers TPI fuel rail fittings (pn 74730, ~$32) for -06 hose that will fit most General Motors TPI fuel injections systems.

If you need a simple way to get to a barbed fitting to connect up rubber EFI hose to the General Motors 2 bbl TBI, your local auto parts house probably stocks GM fuel line repair kits in the HELP section. These consist of 9" of steel fuel line in 3/8" and 5/16" outside diameter with an O-ring and Saginaw fittings 14/16 mm, respectively, on one end and a barbed end crimped on the other. The steel lines are about $4.00 each. These pieces thread into the steel adapters on the GM Rochester TBIs. For a complete listing of various fittings with part numbers, etc. try:

http://www.ag.auburn.edu/users/gparmer/efi/fittings.txt

IMPORTANT: Keep the fuel lines out of passenger compartment and routed safely away from moving or hot parts to avoid damage/excessive heat. For flexible rubber hose use the SAE 30R9 EFI hose which is rated at 250 psi. EFI hose clamps are also recommended rather than gear clamps. Check with someone who knows if you are not sure about your installation. Nobody needs a 50 psi gasoline fed fire to ruin their day!

Note that if you feel your fuel supply is not smooth enough, you can add an accumulator. OEMs often have nice small diaphragm types, or you can plumb in a vertical section of rubber hose tee'd off the supply line (and plugged at the top end). This traps air and uses it to cushion the fuel pressure.

Here is a GM style accumulator (it is about 2" (50mm) long and uses 3/8" tubing):

Or you can make your own:

Fuel filter

Use a fuel injection fuel filter rated for the pressure at which your system operates. DO NOT use a universal carburetor filter - the higher pressure of fuel injection systems may cause it to burst! Position the filter downstream of the pump so that a clogged fuel filter will not over heat the fuel-cooled pump.

Fuel Pressure Regulator

The vacuum referenced fuel pressure regulator is essential. It provides constant pressure differential between fuel at injector nozzle and manifold air pressure [port EFI] or atmospheric pressure [TBI]. This makes the injected fuel quantity solely a function of the injector open time.

If you were to 'cap off' the manifold vacuum port on the fuel pressure regulator, you are reducing the dynamic range of the injectors. This means you will need lower pulse widths at at (giving less control over idle mixtures) and lower flow under boost (restricting the maximum horsepower).

So, in general, for port injectors, have the fuel pressure regulator connected to the manifold vacuum is a good thing. There is very little reason not to do it (though some have argued against it for individual runner port EFI set-ups).

If you have an adjustable fuel pressure regulator (FPR), set the pressure with the fuel pump running, but the engine not running - that's your base fuel pressure (it is referenced to atmospheric pressure).

The regulator is typically at the far end of the fuel rail (after the injectors), but performs its job anywhere, so long as it is after the fuel pump. However, if you have the regulator before the rails, then the full volume of fuel isn't circulating through the rails. Only the amount of fuel actually injected moves, and the fuel can get quite hot, which may require special injectors, etc. Apparently OEM use special injectors, etc., with returnless systems, which is essentially what one has if they put the regulator before the injectors. This can also create problems trapping air on assembly that can cause issues at first start-up.

If you are using an aftermarket fuel pressure regulator, it is a good idea to also install a pressure gauge, since most of these are adjustable. For TBI, use a 0-30 psi gauge. For port injection use a 0-60 psi or 0-100 psi gauge. Most of these gauges will mount directly on a fuel fitting using a 1/8" NPT thread. These are available from most aftermarket speed parts suppliers, such as Summit Racing or Jegs.

Surge Tank

You only need a surge tank if you are using a low pressure pump to supply an external high-pressure pump. Some pumps come with an accumulator after the pump, and these can be left in place.

Wiring the Fuel Pump

To activate the fuel pump, Mega Squirt provides a ground for the fuel pump relay circuit on pin 37. The relay is wired for 12 volts switched from the ignition switch, and the relay is grounded through Mega Squirt [pin 37 on the DB-37 connector].

Mega Squirt will disable the fuel pump when RPM = 0 and enable while non-zero (cranking/running), except for Version 2.00 (and up) embedded software which will perform a short priming pulse, then shut down the pump if the engine is not running after 2 seconds.

You might want to consider a safety switch in the fuel pump circuit when installing an electric fuel pump. Holley has one (12-810, ~$20) that will ensure the fuel pump will not run unless the engine has oil pressure. It stops the pump from running if the motor stalls with the ignition on. Wiring the switch through the starter solenoid circuit energizes the pump on engine start-up. Once the engine has started, the switch continues to provide power to the pump as long as there is oil pressure to keep the switch turned on.

Note: An inertial safety shut off switch should be installed and used to kill power to the pump upon significant impact to vehicle.

These switches are available in junk yards from EFI Fords. The switch is on the drivers side in the trunk, near the trunk hinge, mounted so that it is between the interior bracing and the rear quarter panel (protected from being knocked around if you stuff your trunk full of stuff). It is mounted with the reset switch straight up. Note switch mounting orientation probably matters.

It is Ford Part # F2AB-9341-AA. The wire going into it is about 14 gauge, so it should be capable of handling the full current of the fuel pump.

The markings on the switch show that it has NO/NC (normally open/normally closed) positions so that it should be able to accommodate any possible fuel pump configuration.

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