Viken

As some of you already know, Porsche introduced the normally aspirated 993 in 1994 with a relatively close-ratio gearbox called the G50/21 (G64/21 for AWD). However, cars bound for the United States, Austria and Switzerland, had to have the G50 (G64)/20 gearbox with taller and slightly more spaced gears to meet fuel economy and noise restrictions in those countries. As of MY 1997, Porsche installed only the /20 gearbox on all normally aspirated 993's worldwide.

Recently, I had a G64/21 installed in my '96 C4S. The gears from 2nd to 6th are all shorter and 2nd is slightly closer to 1st while the gaps between all other gears are also slightly smaller. This combination of ratios allows much better acceleration throughout the rpm range of the engine. Previously, I drove around town in 3rd and barely used 4th. Now, I find myself mostly in 4th and 5th while on the freeway 6th can finally be used at legal speeds without lugging the engine. I never used 6th before because it did not accelerate at all from just about any rpm. With the shorter 6th, one can stomp on the gas from 2200 rpm and the car goes.

On the track and in tight turns, I always looked for the "right" gear between 2nd and 3rd the former being too short and the latter too tall. I expect the new shorter 3rd will be more adequate in such situations. The 1.024 fifth will also be very useful on long straights coming out of turns such as at Willow Springs.

During this gearbox transplant, it was discovered that the dual-mass flywheel was starting to go bad. This flywheel is not too reliable and can fail early in some cars. I decided to replace the overweight and unreliable flywheel with a lightweight RS version. This also necessitates the change in clutch and pressure plate. The new flywheel does indeed allow the engine to rev quicker. It takes less time for the engine to reach the more usable power band and the "Varioram" lag I experienced before is much less noticeable. I would estimate the speed at which the revs climb is about 20-25% quicker than before. On my '96, there are no stalling issues and the noise from this flywheel is a muffled "brrr" only perceptible at part throttle. Once the car is under way, it sounds exactly the same as before.

To sum-up, these upgrades are substantial and worthwhile. At least, to me they were. I think any normally aspirated 993 can be brought to life with at least the close-ratio gearbox. The lightweight flywheel is a welcome bonus that might complete the package for many. I was also very pleased by the shop that did the work. E-mail me if you'd like a recommendation.

[ 07-08-2001: Message edited by: Viken Bedrossian ]

Anir

Great post, Viken, and also very tempting. There seems to be little downside to the upgrades.

Would you expect a switch to the G64/21 close-ratio gearbox and lightweight RS flywheel to yield similar improvements in a 1997 993TT?

As I understand it, the stalling with the lightened flywheel is not a big issue with '96 and '97 cars. Am I interpreting the situation correctly? I don't mind a buzz or humm, but would like to avoid the stalling issue.

Thanks again!

Viken

Anir,

The /21 gearbox is very similar to the Turbo's /51 version in terms of gear ratios:

/21:

1st - 3.818
2nd - 2.150
3rd - 1.560
4th - 1.242
5th - 1.024
6th - 0.820

/51 (worldwide):

1st - 3.818
2nd - 2.150
3rd - 1.560
4th - 1.212
5th - 0.937
6th - 0.750

As you can see, 1st through 3rd are the same while 4th is very close. I suspect that by the time you've shifted into 5th or 6th you're already running at stratospheric speeds (read boost) in your Turbo. However, you can always custom tailor the gears on any car to suit your driving style and needs. In the case of the normally aspirated 993's with the /20, the car's downright "need" the closer ratio gearbox.

As to the lightweight flywheel, the benefits are similar in any 993 variation. There are several 993 Turbo's running with lighter weight flywheels. Also, I would imagine the DME would take care of all stalling issues as it does on '96-on normally aspirated 993's.

[ 07-08-2001: Message edited by: Viken Bedrossian ]

Anir

Thanks for the quick reply, Viken. I'll stick to the flywheel upgrade for the TT when the time comes.

I'm glad that your car turned out so well.

Randall G.

Hi Viken,

I wasn't aware that the LUK DMF flywheel had any reliability issues--unlike the original POS 964 DMF. Of course, if the LUK does in fact have reliability issues, that's (more) motivation to go LWF, come clutch replacement time.

What have you heard/learned about the LUK's reliability? Thanks!

Viken

Randall,

My 964 Flywheel totally gave-up on me at 14K miles and was replaced under warranty. At that time, I was told that Porsche was replacing quite a few of these because of reliability problems. When the 993 was introduced, I heard that the new unit made by LUK was much improved and should not suffer from as many failures. However, recently I am told that even LUK is not as great a product as expected. Mine had 25K miles and I was told that it was not uncommon for them to go bad that early.

The best advice I have is to at least closely inspect your flywheel and check for any rubber deterioration.

John D II

Great report, Viken. The lightweight flywheel is an item that I am very interested in and I enjoyed reading your impression.

John

Randall G.

Hi Viken,

My original DMF also failed, at just over 30k miles and barely out of warranty. I had it replaced with an RS LWF. Because of chronic stalling and erratic idle, I convinced Porsche to replace the LWF with the LUK at 50k miles--provided I pay for the labor and have a major service performed at the dealer. This all occurred back around 1994-1995.

I recently had my clutch replaced, because of a sticking-in-gear problem. The last mechanic to work on the car failed to reinstall the bell housing vent and slave cylinder cover (and perhaps didn't seal/lube components), which allowed the input shaft and clutch center to rust, causing the binding. My clutch parts only had 40k miles on them, but I went ahead and replaced
them all, as compared to cleaning up and reinstalling the existing parts. The LUK DMF, with some 57k miles, looked fine, and was reinstalled.

I'm just now learning that the OBDII cars work well with LWFs. Considering that my '91 C2 has a '97 Varioram engine (and 993 6-speed), I suppose I can safely swap over to a LWF, if my LUK ever gives out.

Finally, I'm glad your transmission mods have worked out. Sounds like everything works very well.

NRK

A related question: is the reason the LWF works best in 96+ solely because those cars have Varioram, or does it have something to do with the DME or other factors? I'm curious because I have a '95 car with Varioram and am considering the LWF conversion.

Steve in SLO

Great post, Viken. I have a G50/21 waiting for the same swap.
Additional information for those who might not know about the /21 gears vs the /20 (US)gears: 1st is the same, 2-5th are approx 10% lower, and 6th is approx 5% lower.
I had thought about replacing the stock R/P in my /20 trans with an 8:32, which is 12(?) or 14% shorter than stock, but did not want the top end to suffer so much because of fuel mileage on the freeway.
After reading this report, I can't wait.

Viken

It is my understanding that the DME on '96-on cars is able to make adjustments to deal with the quicker drop in rpms. In my case, I felt no difference in the way the revs drop just below 1000 rpm's.

Viken

OK, here are the actual ratios:

/20 (US gearbox):

1st - 3.818
2nd - 2.048
3rd - 1.407
4th - 1.118
5th - 0.928
6th - 0.775

/21 ('94-'96 ROW gearbox):

1st - 3.818
2nd - 2.150
3rd - 1.560
4th - 1.242
5th - 1.024
6th - 0.820

E. J. - 993 Alumni

Viken, Where did you get your box and how much should one expect to pay for such a thing?

Thanx,

Greg Fishman

EJ
When it comes time to do a clutch and flywheel change I would look at doing this upgrade. It does add up pretty quick because you would want to change the 1st gear shift forks, and first and second synchros which are about $1500. If you change out gears you are looking at around $700-$900/each for Paul Guard gears and probably 50% more for Porsche Motorsports. Then there is the labor and hopefully your ring and pinion is in good shape if not that is around $1500 and you might as well get a real LSD another $1000 or so. If you were to change you probably should go with the ratios for the RS Club Sport since you spend a lot of time at the track.

You can drive my car in a couple weeks and see the difference the close gears make.
Greg

[ 07-09-2001: Message edited by: Greg Fishman ]

Brian 96C2

Viken,

I am putting together a data base of components that I will/may some day install in my 993. My car has relatively low miles now, but in case the fly wheel does need to be replaced do you have the part numbers for the RS fly wheel, clutch, and pressure plate? Thanks.

Brian