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August 1999

In Search of Lost Horsepower -PART I
By Steve Grosekemper

A growing concern of many Porsche owners is where can they spend that extra $500.00 to $1000.00 to get the most power out of their car. I hear the same story time and time again: "My friend has the same model car as I have, and his car is much faster than mine. Should I get a Chip/muffler/K&N/headers/etc.?"

We have all heard of the cars that are a little faster than the rest. Why they are faster and how to make your car one of these cars is today's question and answer.

It is very difficult to make one small change to a car and get a significant increase in performance. However, if you make 10 small changes, the accumulated increase in performance can be substantial. If you go to a driving event and locate all the Porsche technicians' cars, you would probably notice that they are the faster cars in their respective classes. Is this because they know where to hide a nitrous oxide bottle where no one else can find it? No, it's because they know how to get 100% out of the cars that they are driving. After all, isn't that their job? (Well, at least we know it's not their driving.)

The first area we are going to look into is air/fuel mixture charge. In order to get the most power from an engine, you have got to get the largest amount of air and properly mixed fuel into the engine. Just because you are crushing the accelerator pedal under your foot does not mean you are getting the throttle plate completely open. When you do get WOT (wide-open throttle) a signal is sent to your fuel injection to richen your fuel mixture. This is done to lower combustion temperatures and to increase power output. If you don't get WOT, you get less air, less fuel, and less power.

To check for WOT operation is quite simple. Get an assistant to press the accelerator pedal  to the floor (engine off, of  course) while you check for throttle plate movement. You should feel a noticeably firm stop at the floor. All cars have throttle stops. The throttle plate should be open almost a full 90 degrees from idle position. It is also important to check for binding. You should be able to turn the throttle plate another degree or two from the WOT position. This will ensure that no linkage will bind, causing failure or sticking.

If you don't have 100% throttle opening, here is where to check:

911s '65-'89: The most common cause for throttle linkage play is failure of the bell crank bushings. These are plastic bushings located at angle points for the linkage. They can be found at the pedal assembly, the front of the transmission, and the top of the engine. The top engine location is the most common failure due to heat. Replace all bushings as necessary and make a final linkage adjustment. (356 linkage is quite similar)

911s  '89-'97 (964/993): These cars are notorious for having loose/incorrectly adjusted throttle cables. When this happens, not only do you not get the extra fuel and air, but the resonance flap may not open either, causing a severe loss of maximum power. The adjustment can be made under the car at the firewall (threaded adjustment sleeve) and at the throttle pedal itself.

914/4 and 914/6: These cars are a combination of cables, bell cranks and links. 914s have a bell crank at the pedal assembly just like 911s. From there, a cable operates the throttle plate on 

4-cylinder models. This is adjusted with a barrel nut at the throttle plate arm. 914/6s have a throttle cable that connects to another bell crank at the transmission and then to a bell crank at the top of the motor (just like a 911). The six cylinders' primary adjustment spot is at the transmission bell crank where the cable attaches.

924/944/968/928 all years: These cars have throttle cables that can stretch as well. Adjustment can be made at the firewall. Some models have bell cranks in the engine compartment as well. The pedal stop screws into floor. (924-944)

Note for 928 Automatics: These cars have transmission kick-down switches under the throttle pedal. These switches and pedals can become "mis-shapen" due to aggressive pedal application.

This can cause severe loss of performance due to incorrect downshifting points. They need careful inspection as well as the throttle input cables for the other models with automatics. The throttle input cable can be found at the throttle plate and at the transmission.

Last but not least, we can not forget the air filter element. A clean filter will flow much more air than a dirty one. Re-useable filters such as K&N filters must be cleaned and re-oiled properly. A K&N that has been improperly oiled can flow at half of its original flow rate, defeating its entire purpose.

Good Luck!