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Power Production Basics

The key to making power is increasing the mass flow of oxygen. Adding the right amount of fuel is also important, but not nearly as difficult as getting the oxygen through the motor. There are three ways of getting more oxygen into the motor. One is to increase the density of the air charge through compression using a turbo or supercharger, preferably with an intercooler to increase density further. Another way is to increase the rate of air volume flow (usually measured in cfm), while holding density constant. The third method is to increase the percentage of oxygen in the air (usually done with nitrous oxide, N2O), or even the fuel. Getting the oxygen (and the fuel it's bonded with after combustion) out of the motor is simple enough. For turbo motors, choose the biggest A/R turbine you can use and still have acceptable lag, and then the biggest exhaust you can fit/afford after it. The turbine will provide more exhaust backpressure than you want, you don't need or want any more backpressure from the rest of the exhaust.

Air Charge Density

The most efficient way of increasing air charge density has proven to be the turbocharger used in conjunction with a high efficiency, high flow intercooling system.

Turbos

A turbocharger is a centrifugal exhaust driven compressor. They are similar to many superchargers that are commonly available for late model muscle cars, except that exhaust blown through a turbine is used to spin them instead of a belt. A wastegate is used to allow some of the exhaust to bypass the turbine (exhaust side of the turbo) to avoid spinning it too fast at higher engine speeds. The wastegate allows a turbo to maintain a constant boost level (which can also be thought of as backpressure in the intake manifold due to resistance to flow through the motor) once it has reached a high enough speed to begin opening the wastegate. This is accomplished by using pressure from the outlet of the turbo to mechanically open the wastegate at whatever pressure the wastegate actuator is designed for.

A common modification for turbocharged cars is to adjust the boost pressure that the wastegate opens at, in order to use higher air charge pressure to increase density and make more power. For more information on this, see Boost Control. Also, different turbos have different flow and boost capabilities. To see compressor maps from Turbonetics for the commonly available compressor sizes, see Compressor Maps.

Intercoolers

Another way to increase power is to reduce the temperature of the air charge. Since compressing the air with the turbo makes it much hotter than before, we can use outside air to cool it back down, which increases the density (and the power) that much more. The device used to do this is commonly known as an intercooler. Technically, people in the air compression industry refer to an air charge cooler that goes after a compressor as an aftercooler, and an air charge cooler that goes between multiple compressors as an intercooler. This is why you may sometimes hear people refer to what we think of as an intercooler as an aftercooler.

There are two common ways of intercooling a compressed air charge, usually referred to as "air to air" and "air to water". An air to air system uses a charge cooler that must sit in the airstream to work properly, preferably in a high pressure area such as the very front of the car. After being compressed by the turbo, air flows through it like coolant through a radiator before it enters the cylinders. An air to water system is similar, but can be mounted anywhere, because the charge cooler is surrounded by a water jacket and does not need an air stream from outside the car to cool it. Water is pumped through this water jacket to a remote radiator that does need to be exposed to an outside air stream, but does not have to be particularly large because water can carry more heat than air.

Intercoolers can be made at home fairly cheaply (if you can weld) using parts from intercoolers off other cars. Chris Roth made a front mount air to air charge cooler using a stock Volvo intercooler. The bottom line on this intercooler is that it cools the air well, but it a little restrictive for our purposes. It's acceptable on the stock motor (regardless of how high you turn the boost up), but not something you'd want to use once you start doing a lot of porting work on the motor. Chris solved this by making another one that used two cores. It works ;-). Carl Morris made an air to water unit using a Thunderbird intercooler in the stock location. It seems to work, but testing hasn't proven anything for sure because the stock turbo currently seems to be limiting his output. Richard Thompson has also done something similar for the Merkur, and is selling a complete air/water system based on the Tbird intercooler. Enrico Pavia installed an Audi A4 intercooler in his SVO. The recommended vendor for new intercoolers and intercooler parts is Spearco.

Engine Airflow

Volume flow (cfm) is one of the three factors that control mass oxygen flow, and therefore power, as mentioned above. Every single opening and passage that the air charge must pass through will effect the flow, from the opening in the bodywork that allows the air to get to the air filter assembly inlet, to the very tip of the exhaust pipe. Stock Ford 2.3 turbo motors are designed to flow a maximum of about 150cfm after the turbo. The factory air filter assembly and exhaust flow even less than needed by the stock motor, in order to minimize noise. Therefore, they are the first things to change when looking for more power. In the early SVOs and late model Tbirds, a cam was used that increases low RPM performance at the expense of maximum flow, which also causes maximum engine flow to be lower than 150cfm. Once these problems are solved, the rest of the system (intercooler, throttle body, intake manifold, head, and exhaust manifold) are pretty well matched, and will need upgraded as a group (except the throttle body, no upgrade is needed for it) if higher flow levels are desired. For anyone not wanting to do it all at once, replacing or porting the exhaust manifold first will give the best results. 200cfm is the maximum realistic flow possible when modifying the stock system, and can be realized using products and services from Esslinger Engineering. Also available from Esslinger are a very expensive aluminum head and intake manifold system that can reach flow levels in the 240cfm range. At higher than stock flow levels (180+ cfm) an aftermarket intercooler is highly recommended. The best information available currently regarding air flow work (as well as air charge density improvement) for the Ford 2.3 turbo motor is the Tiny Avenger series of articles that were written for Muscle Mustangs and Fast Fords magazine. While not 100% complete or accurate, the article did a good job of showing the potential of a near-200cfm motor when the air charge density is high enough.

Computers and Fuel System

The good news for 2.3 TurboFord owners is that the stock computer and fuel injectors for the late model SVOs and Tbirds are very good, and will support 300+ horsepower, and far more if higher fuel pressures are used for nitrous oxide systems. The Tiny Avenger article showed the stock computer to also be capable of adapting reasonably well to 42lb/hr injectors for even more capability, but 52s were too much and caused a lot of problems. 300hp will get a 3300lb car into the 12s at over 105mph, so until you are at or very near this level, sticking with the stock late model computer and its 35 lb/hr fuel injectors is highly recommended. Anyone running over 250hp should use an air-fuel meter that reads their oxygen sensor signal to detect fuel supply problems such as a bad fuel pump or too-small/clogged injectors, just to be sure. Of course, having fuel of sufficient quality to support your boost level without detonation is always a requirement. If you have difficulty obtaining fuel of sufficient quality, see Making Your Own Race Gas.

Ignition

More good news here. The stock ignition is very good on the TurboFord vehicles, and the best results will almost always be obtained by using fresh factory stock parts whenever ignition problems develop. For more information see Ignition Maintenance.

 

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Page last updated: Friday, 28-Oct-2005 11:26:02 EDT