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Flathead Part 4 Sizing a Turbo

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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


  • Additional information about rigid media:

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.

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


  • Additional information about rigid media:

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.

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.

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.

  • Formulas:

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).

  • Tables:

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).

  • Table 2: Evaporation Rate

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.

  • Table 3: Temperature drop across media (@ 500 FPM face velocity)

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.

  • Table 3: Air Density Ratio: Density Ratio for Various Elevations and Temperatures.

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

 

  • Table 4: Air Changes suggested per hour.

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:

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