Last month we went through many of the modifications that I did on my 930 Turbo’s engine. Now we were running around with somewhere in the neighborhood of 425 horsepower. But I noticed something, on any racetrack that I took the car to, the transmission gearing just didn’t seem right.

The 930’s transmission, from the years 1977 up through 1988, was a 4-speed unit. It is a very strong unit and was used in the Porsche racing cars from 1977 RSR turbo’s up and through the very powerful, 800+ horsepower, Moby Dick 935 of the early eighties.

In it’s stock form, the first gear of the car, although able to propel you from a standing start with enough force to give you a slight whiplash, was really unusable on the track. I also noticed that the stock 4th gear in the car was geared way too high, for over two hundred miles an hour! Now that sounds so tempting, to be able to go two hundred. But in reality it would take an estimated real horsepower of over 700 to get this car, of this weight, to go 200. And it would need a long; long straight away of over three miles to obtain a speed of 200.There isn’t a track here in the northeast that has that kind of running room. I found myself only using second and third gear on most tracks with an occasional quick shift to 4th on some tracks. Another thing to remember, especially with a turbo car, is that you always want to keep the engine in a rpm range where the turbo is spinning fast enough to make boost pressure. If the car has a good exhaust header this engine rpm is somewhere around 3,000. In my car, due to the bigger turbine wheel in the turbo, my lowest engine rpm to keep the turbo spinning is around 3,800. This information is also critical in determining your gearing.

On up shifting or down shifting you don’t want to let the engine speed drop below this predetermined rpm. If it does you will fall out of the power band. If you’re out of the power band, when you step on the gas and expect to get gobs of engine power there will be none. You will be experiencing a bad case of turbo lag. You’ll step on and nothing will happen. This is not as apparent on a normally aspirated engine. Never the less, transmission gear is critical for optimum performance.

So, out comes the motor again, this time, to access the transmission. I gave my friend from Powerhaus 2 a phone call to discuss my gear change options, and a lot of options there are. I felt that on the track the stock third gear set up was the only gear in the transmission that felt really usable. Considering the price per pair of gears, $595 used, I was glad to reuse at least the one ratio. I brought my 1st gear ratio up high so that it was usable through most of the slow speed turns we would be encountering. Keep in mind that the term “slow” is relative. I didn’t want the rpm to fall off between shifts. Following the gear chart, I selected a second gear ratio almost right between my 1st and 3rd. The letter designation of the 3rd gear ratio, as per Porsche, is SP. SP is the stock ratio for most 930 Turbo’s. With 25” tall tires this will give you a top 3rd gear speed at 7’000 rpm of 134 mph. We chose a 2nd gear ratio of QU that gave us a top speed in 2nd of 114. The 1st gear we chose was a very high KW. Top speed in 1st, 89 mph. Now for 4th we dropped the ratio from the original WL top gear to a VM that gave us a top speed in 4th of 173. The rpm drops between shifts went as follows. 1st to 2nd-1800, 2nd to 3rd 1500, and third to 4th 1350. This was a huge improvement in drivability and performance on the track. Now all 4 gears were very usable. For the street 1st gear would be a little to tall, requiring to much clutch slippage to get the car underway. I would opt for a slightly different gear ratio for a street car.

Unfortunately everything is a compromise; The more the car becomes a track car the less of a street car it will be. For me; There is no middle ground.