Efi Engines - Factory Five Racing MK4 ROADSTER Assembly Manual

EFI Engines

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There are three things an engine needs; air, fuel and spark. If you allow more of each of these into the
engine, it will make more power.
Throttle Body
Stock 87-93 Mustang size: 58mm
A 65mm throttle body work well up to 350hp. Ford Racing, BBK, Jegs, Summit Racing etc... sell many other
sizes.
Mass Air Meter
Stock 87-93 Mustang size: 55mm
In order to increase the flow of air above 5000 rpm, upgrade from the stock mass air sensor. Aftermarket 70
mm or 75 mm mass air units are an excellent choice and have proven effective. If the mass air meter is changed
make sure it is calibrated for the injectors you are using or you will have to change the injectors too. Pro-M or
Ford Motorsport meters work the best. Usually the mass air meter is larger than the throttle body.
Fuel Injectors
Stock 87-93 Mustang size: 19lb/hr.
The stock injectors are good for exactly that, a stock engine. If upgrading parts, step up to 24 lb/hr injectors.
They are good up to about 400hp. Make sure that you have the mass air sensor calibrated to the injectors you
use.
Upper Intake
The next logical step for breathing is a more free flowing intake manifold. There are a number of intakes
available from different companies (e.g. Edelbrock, Trick Flow). Ford also makes a good intake, the cast 1993
Cobra intake from Ford Racing.
Heads
The 5.0L Mustang aftermarket is full of aluminum and cast iron heads for the small block Ford. Our favorites
are the Edelbrock Victor Jr. and the Trick Flow aluminum heads. These both flow very well, have stock
exhaust port heights which allows the use of our headers and not only give you extra horsepower but also
remove 50 lbs. in the process.
Cams
If you need to pass emissions testing, use a cam with a CARB number. We like the Ford E303 cam. We have
used it with success in our racecars both naturally aspirated and in boosted applications. If building a more
radical engine, match the cam to the combination.
Headers
Stock 1987-1995 Mustang: 1½" OD
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