For years, until 1989, the strongest of the Porsche transmissions was the 4-speed 930-type transmissions from the Turbo cars. The earlier 915-type gearbox was and still is a good transmission for all the earlier bodied cars. It will work flawlessly until the horsepower is raised beyond 300 or so. After that, a variety of problems will start to crop up. These 915 type transmissions just weren’t engineered to handle that kind of power. The gears are fairly thin, which is one of its Achilles’ heals. Another is that the case tends to swell under load. This would cause the gears to strip or in a worse case scenario, the housing to shatter. When the 930s were introduced in ‘75 they came through with the 930-type designated transmissions. These units had heavier, thicker gears, along with a beefier differential section, able handle the horsepower and torque of the new 930 Turbo engine. In ’87 the G-50 came to be in all 911 models. The G-50/01 uses later style synchronizers, which makes this unit much easier to shift then its predecessor. Porsche felt that this G-50 transmission was still not able to handle the power of the 911 Turbo so they kept using the 4-speed in the 911 Turbos until ’88. For one year, the 1989 911 Turbo came with a 5-speed transmission dubbed the G-50/50. This unit had a larger ring and pinion section (215mm) than the G-50 along with a stronger intermediate plate and a slightly different gear ratio.

When I first modified my 930, in the old days of our Bridge Hampton Driver Ed events, I knew that the gearing of the transmission was just not right. 1^st gear was just too low for anything but getting the car to move off from a dead stop and 4^th gear was too high for all but the Autobahn. That left me with only two useable gears. After some deliberation, I decided to change 1^st, 2^nd and 4th to have a more useable, track, transmission.

Years later, my original 930 had gone through quite a few metamorphoses. The engine, which started out stock and producing 285 horsepower, went through three specific stages. The first round of modifications brought the horsepower into the mid 400’s. With the second set of modifications, admittedly extensive, we saw the horsepower catapult beyond 700. Through all of these changes, that 930 transmission handled it all. Believe it not, the engine was sold after running for two track seasons and was de-tuned to produce anywhere from 480 to 650 horsepower, at the customers request. And all that from a 3.3-liter engine with stock pistons. We have now completed my new 3.8-turbo engine. Expected horsepower should be over 900. We had a tough choice to make as far as a transmission was concerned. When I sold my 3.3-liter engine, the car we were putting it into was a converted ’81 911. The ’81 911 came through with 915-type gearbox. That wouldn’t have held up very long, even with the engine in its new “detuned” state. So, there went my “Race-geared” 930-type transmission, transplanted into a new home

Lying around the garage were 3 different types of transmissions. One was a short tailed 1987 G-50, the other a G-50/64 from a 92 C-2. The G-50/64 has the same basic internals as the ’87 G-50. But, it is considerately longer. The last one, a G-50/21, is a 6-speed with a factory LSD. I really wanted the 6-speed but that would have necessitated a lot more sheet metal to be removed. So, I chose to use the shorter G-50. At least that would only require the torsion tube to be cut away. The G-50 is a bit longer than the original 930-type transmission.

The 911 (up to ’86) and the 930 (before ’89) had a straight torsion tube that runs from one side of the car to the other. The later cars have a “U” section in the middle of the tube that allows enough room for the longer G-50. After the transmission is installed, the pedal box has to be updated and new hydraulic lines from the clutch master back to the new clutch slave have to be routed. The older 930 worked with a cable-operated clutch and the newer G-50 works with a hydraulic clutch setup. One benefit of this is lighter clutch pedal pressure.

The 1987 G-50 also has some inherent weak spots that will have to be addressed before it is worthy of “track work.” The first thing to be changed is the weak cast aluminum shift fork. It will be replaced with a stronger forged piece. Next, the brass synchronizer rings are discarded for more sturdy steel racing units. These will be used on all gears except for 5^th. 5^th only sees half the use that the rest of the gears will see, the steel syncro isn’t really needed here. Also to be replaced is the side differential carrier plate. This will be changed for a billet piece. The billet unit is thicker and much stronger. It should help the case from distorting under load. This G-50 will also have the gear ratios changed so that all the gears will be useable on the track. Race-type gears are built stronger, with fewer teeth, than their stock counter parts. On this G-50 I kept the stock 3^rd and replaced 1^st, 2^nd, 4th, and 5^th. With a 13/34 1^st, 19/34 2^nd, a 22/31 3^rd, 23/27 4^th and a 25/25 5^th this transmission should be a lot of fun on most all the tracks I’ll drive.

Well, we’re now ready to begin installation of this new engine/transmission into my ever-changing dinosaur. Hope to see you at the track.