Regarding 993 vs 996....if you want a 6 speed I would look for a 993 G50. The 996 gearbox is rebuildable, does use lots of G50 parts and is certainly not throw away but it is harder to work on than a G50. The 996 parts are pressed on the shafts and require a big press to rebuild. I haven't done the work myself (no big press) but I've had mine done.

If you decide on a tiptronic I would certainly look for a 996. They are a dramatic improvement over the 993 tip.
Jim

 

Thanks a lot Jim, thats the kind of info that I knew you guys would have.

Dave

 

"I'm in Edgartown"
i lived in edgartown when i went to high school (mvrhs)...class of 1989; did you go to school on the vineyard?

 

No,
The 4wd version is known as the G64 and the 2wd tranny's are the G50. If your building a winter fun car you might want to look into using the 4wd transmission from the 964. It's a little more expensive but the system is purely mechanical and usually prefered over the 993 AWD for winter driving.

 

jason, I think that you have it backwards.. the 964 C4 tranny is a viscous coupling fed via a complex electronic control system that included accelerometers! (at least my 89 C4 was..) The 993 C4 system is a more simple fixed 40/60 power bias split through the diff.

Coleman.

 

The 993C4 limited slip differential is a standard 22/40% mechanical unit but drive to the front wheels is through a viscous coupling (5/95%). Whereas the 964C4 is entirely mechanical, front to back (31/69%). HERE is one of many discussions comparing the two.

 

964 G64 uses an epicyclic gear train to fix the front rear torque split 31%/69%.
In addition there is a lockup clutch pack to transfer more torque to the front if required.The system is electroniclly controlled and the front drive cannot be disconnected.

The 993 uses a viscous coupling hung on the front of a 6 speed G50 box.Front torque is dependent on front/ rear tire speed only. Standard car has very slightly larger diameter front tires so the split is around 5%front/95% rear .
If the front tires are very slightly smaller than the rears, there is no front drive.The drive to the front can be disconnected .

For your project it sounds like the 993 C4 box is the best choice because you can run it 2wd until you get the torque tube/front diff sorted .

Good luck,

Geoff

 

I agree. Buy the 993, enjoy the benefits of Porsche engineering and give me the other $20k that you would waste on the project (as a consulting fee ).

 

heh, I think I'll just give the beetle the benefit of my own engineering and make it happen. The car is a ground up project. Stiffened chassis, some cleand bodywork. I already have the SLA pushrod front and experimental rear suspension designed and ready. Roll centers, camber change rates, roll axis inclinations, ackerman angles, all that, done on paper. Just a matter of laying it to final design once a final driveline is chosen and I decide on what steering knuckles/ wheels/ brakes to pilfer. I realize its a big project for most people to get their heads around, but honestly, its no big deal for me. Its what I have been doing for years.

Dave

 

Nice! I grew up in Central MA, but my wife and her family grew up here. They all went to MVRHS. You might know my brother in law Chris Dolby. We was a soph when you were a senior. I'm married to his youngest sister Linley.

Dave

 

Dave, I was partly kidding (I really could use the $20K toward a 993). You are more ambitious than I. Good luck with the project. Gary

 

Allright guys, its really starting to come together for me on paper. I think I know what I am looking for.

Right now, the best case I think would be the G64-20 out of a USA spec 993. The gear ratios for 2-6 are all a little higher than the G64-21 or the 996's G96. Preliminarily I am thinking that this is a good thing because with the substantially lighter weight than a 993 or 996 (I figure I will hit about 1950-2050 lbs) and power in the range of the twin turbo cars I am afraid that I will have trouble getting the power down. (400 BHP or so, with a 100HP nitrous shot on top for infrrequent use(making 500 HP total)) At 400HP in the car it puts me at the equivalent of a 993 with about 680 HP.

I might be wrong on that though, and I really would love some input from you racers out there.

From a suspension standpoint I do nto think that I will have an issue with getting the power down. The car will use 4 wheel independent suspension, designed to work together and with the wheel/ tire selections, drive cheme, and weight balance. I definitely will be using adjustable geometry on the suspension, and adjustable dampers/ brake bias/ antiroll bars.

There are a couple interesting points on the transmission side.

1) As I understand, the G64 and G64 are similar operationally, but the G96 is not designed to mount the viscous coupling for the front drive off the transmission. On the 993's G64 the viscous coupling is mounted off the front of the gearbox, while the 996's viscous coupling is part of the front drive assembly. The part that is alluring about this is that from what I read this moves 120 lbs from the rear of the car to the front of the car. What I potentially will give up in steering feel, I can gain in traction. Additionally, becuase my experimental rear suspension has the ability to provide a constant amount of anti-squat as the suspension compresses, I can further tune mass transfer and balance under acceleration. (I initially designed the suspension system for MOTO GP and Motocross use, its pending patent worldwide. Another squat manipulation suspension that I developed specifically for bicycle use has found great success in the bicycle industry. You can read about it at www.dw-link.com if you are interested. )

2) After reading about the 964 drivetrain, it sounds awesome, but I am a little afraid of the complexity. I'd rather stay simpler if I can.

All in all, now I am left with two questions.

1) Some of you racers know weights, tires, gear ratios, and the power range that I'm taking about pretty well. Will the 996's ratios [3.82 | 2.20 | 1.52 | 1.22 | 1.02 |.84] be too low to put down the power in 1st through 3rd? I could care less about top end. I am planning to use tires at least as large as on any 993/996, the chassis will be designed and body modified to suit.

2) I have searched for pictures / measurements of the 996 / 993 front gearbox sections and have come up empty. Does anyone know of an archive somewhere that I can see some parts?

3) Am I missing anything crucial?

Thanks for all of the help so far guys.

Dave

 

Thanks Gary. I think most of us could use 20K for something! haha

 

FWIW I run around 700 hp on my 3000lbs 2WD 993TT with 315s Sport Cups in the rear, and the car hooks up pretty well, unless you rev it and drop the clutch in 1st.

I would change the 1st gear (and 2nd.) into something taller, they are very short for the kind of acceleration you will get, you can never shift into second before hitting the rev limiter. This is a nice to have rather than a must have.

Other than that, I would go with the cheapest gearbox you can find in great condition, be it a G50 or G 64/21 or G96 unless you definitely want to go 4WD in the future, then you will need the G64.

At this level of HP/lb the slight difference in ratios will not make much difference in times, getting used to the car and having a great suspension setup will (very) largely offset that.

Jean

 

Thanks Jean,

So based on what you have said, it sounds like maybe picking up a G96 and altering first and second gears to be a bit higher may be the best case scenario.

I like the idea of AWD'ing the car because I already have to build bew front suspension to match the rear. I figure if I am already doing it, why not go all out. That plus adding a little weight up front could be a good thing I think.

Dave