I had a 6 speed installed on my 1990 and the mechanic basically pushed the engine back to get the transaxle to clear. I was under the impression that they just kind of slide in but he said its pretty tight. For any of you that have done or seen a 6 speed install how was it done? I did notice that the axles rake forward now but can't remember if they were that was with the 5 speed or not.

Pete

 

This is what it should look like, never heard of any issues

 

Thanks Bill. My 6 speed came from a 993tt box that Bill Rader modified with a new nose cone up front. Its definitely longer than the 5 speed. Are the non-turbo boxes different (shorter) in length? I does make since that the extra gear would increase the length but somehow I thought they were the same as the 5 speed.

Pete

 

Now that’s just Porsche ****

Dont think my car’s under belly was that pretty when new👍😁

 

^^ I don't think my cars top surface is this clean. I thought my car was kinda clean until I saw this picture. I'm now enlightened and disgusted by my filthy undercarriage. I think pictures like this should come with a SPOILER ALERT. DO NOT VIEW UNLESS YOU ARE PREPARED TO SPEND THE NEXT 6 MONTHS UNDER YOUR CAR TRYING TO MAKE IT LOOK CLEAN.

 

The cases for the n/a and tt trans are the same, the difference is in gearing and the awd cars have the front drive mechanism in the nose cone, so if tht was swapped then the exterior dimensions are the same

here's a pic of the rwd and awd versions of the 993 trans

 

Thanks again Bill. This is what I thought. Additionally my understanding was that they are the same length as the 5speeds. Do you have any info on this? Pete

 

I don't have any measurements

Here's a better pic of a 993 g50/21 prepped for install in a 964

 

964 g64


964 g50

 

Looks familiar! Here’s mine sitting at BRM (Bill Rader Motorsports) I don’t have a pic of it installed but I’ll try to get one.

 

Bit of an update-

I reached out to a few builders about this and Roger at CMS responded that the 993tt has a 9" rear ring as opposed to the 7.5" on non turbo axles and as such has a 1" longer bell/diff housing. Turns out that the G50/52 964 turbo axle also has the larger R&P and it seems maybe a larger housing as well. Now I'm left wondering how the extra length was delt with from the factory. In the case of the 964, the turbo and n.a models used the same front crossmember for the front t-axle mount. So the only thing I can see is that the G-body rear engine carrier type used on the turbo models actually places the engine 1" further back on the chassis than the n.a. type engine carrier. The fact that the 993tt also used the g-body type engine carrier supports this idea. Pic I stole from FVD of the 993tt carrier- notice that its curved:

A 93T box, converted to 2WD will be exactly 1 inch longer than a non turbo 993 2WD box993T box, converted to 2WD will be exactly 1 inch longer than a non turbo 993 2WD boxA 993T box, converted to 2WD will be e


Is this theory possible? Do the turbo cars in fact use the g-body type carriers to move the engine back to accommodate a larger R&P? Simply modifying the rear carrier may be one option. However it may not be enough and locating more weight to the rear is not exactly what we need regardless of whether or not that is what the factory did.

The t-axle is going to be torn down again at some point (builder used the wrong ratio for 1st...) So IF I can change out the R&P and bell housing(etc??) for a shorter unit the axle should fit as normal. If the 5 ad 6 speed bell housings are interchangeable then a used housing is possible. This is the best solution.

I may also be able make a custom transmission carrier that would lower the nose 2cm or so and bring the entire engine/axle assembly forward.

Pete

 

Interesting, I learn something new everyday

Since 1978 turbos have always had the engine pushed back further than in the n/a cars, I hadn't realized that had carried over to 964 and 993, I'm not a turbo guy

 

The gap you have to replace belts between the TT and a NA motor is different in a 993. A lot bigger gap in a NA car for sure.

 

Not the best pictures but the trans on the left is a G50/03 5 speed and on the right a G50/20 6 speed. They are identical in length and either bolt up to a 964. As you can see the nose cone is different but the mounting points the same. I have an AWD trans as well and I have 2 C4's modified to C2's. One has a G50 5 speed and the other a G50 6 speed and they all measure the same with no fitment issues.




G50/21 bolted into a C4 converted to C2. Still work in progress.



As far as the gap between the turbo and C2 for belt changing on a 964 I don't believe there is a difference although the fan is from the 930's and the belt used for the A/C on the turbo is different using a wider belt vs the V belt used on the C2's. This definitely complicates changing. out belts.



Best pic i could find for comparison.

 

Very interesting about the belt change. It seems this is the case that the engine is farther back in the 993tt- and maybe the 964t as well??

This transaxle is really a tight fit. Since I need to have the mainshaft switched out anyway (builder put in the wrong ratio and the main shaft is longer on the large pinion units) I'm leaning towards changing the bell housing and ring and pinion if the builder has access to most of the parts needed. Turns out he has a new Porsche 3.15 mainshaft which is the ratio I want. That will give me basically a g50/21 with a higher 1st and lower 6th.
13 41 3.154

17 37 2.176

20 32 1.600

24 30 1.250

32 33 1.031

28 24 0.857


Thanks Anthony. It seems only the larger ring and pinion units are longer. I measured my 5 speed and the 993tt 6 speed that I have converted to 2wd and the 6 speed is definitely longer by several cm.

Pete