ROW Gearing and Light Weight Flywheel FAQ

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The purpose of this FAQ page to help Porsche 993 owners answer questions they may have regarding gear ratio and light weight flywheel changes.   The parts list can be used as a reference of all the parts in the gear box. 

Below are a listing of the parts and part number for the clutch and flywheel

ID Part number Name QTY
28 928 102 151 01 cheese-hd. screw 9
27 931 102 111 00 ball bearing 1
26 964 102 239 31 flywheel 1 RSCS Flywheel
25 999 119 017 01 cheese-hd screw  9
23 964 114 012 02 two mass flywheel 1 Standard 94,95 
23 964 114 012 52 two mass flywheel 1 Standard 96+
24 999 052 169 00 ball bearing 1
ID Part number Name QTY
1 964 116 014 90 carrier plate (Clutch) 1 94,95
Alternative parts:
964 116 013 51
964 116 013 52
964 116 014 51
964 116 014 52
1 964 116 014 91 carrier plate (Clutch) 1 96+
Alternative parts:
964 116 013 62
964 116 014 62
1 964 116 011 61 carrier plate 1 RSCS Clutch
2 964 116 027 02 pressure plate 1
2 964 116 028 03 pressure plate 1
2 964 116 028 53 pressure plate 1 Turbo
3 999 510 015 02 cheese-hd screw 9
3 N 014 715 3 cheese-hd screw 9

Viken Bedrossian's close ratio gearbox and lightweight flywheel report 
posted 07-08-2001 19:00
Posted on Rennlist Discussion Boards   » Air/Oil Cooled Discussion Areas   » 993 Forum   » Close-Ratio Gearbox & Lightweight Flywheel

                                                                                            Close-Ratio Gearbox & Lightweight Flywheel 

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.

Here is a part number list courtesy of Viken for his clutch and  lightweight flywheel

N/A 993
Item  Part Number     Description          Qty
1       964.102.239.31  Flywheel                     1
2       964.116.011.61  Clutch Disc / RS        1
3       964.116.028.90  Pressure Plate / RS  1
4       944.116.080.00  Release Bearing       1
5       950.116.813.30  Clutch Guide Tube    1
6       964.114.143.31  Starting Ring Gear    1
7       928.102.151.01  Bolts                            9
8       N.014.715.3        Socket Screw 8 x 45 9
9       931.102.111.00  Pilot Bearing              1
For 993 Turbo clutch and pressure plate part number

993 964.116.028.53 - Turbo pressure plate
        964.116.014.91 - Turbo clutch


Here are a list of the Q/As posted on the Rennlist

Q -  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. 
(Question by Anir)
A -  The /21 gearbox is very similar to the Turbo's /51 version in terms of gear ratios:


                             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

                             /20 (US gearbox):

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

As you can see, 1st through 3rd are the same compared to the twin turbo 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.
(Answer by Viken)

Q -  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!
(Question by Randall Granaas)
A -  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
(Answer by Viken)
Q - 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.
(Question by NRK)
A -  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.
(Answer by Viken)
Q -  Viken, Where did you get your box and how much should one expect to pay for such a thing? 
(Question by EJ)
A -  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.
(Answer by Greg Fishman)
A -  E.J.
Although I'm not Viken, I can tell you that I bought mine from a U.K. wrecking yard for about $2500+shipping and import fees--probably cost me close to $3K to have it on my doorstep. Mine is a G50/21 (RWD) trans with approx 45K mi on it. Before I put it in, I will have it inspected to see if anything needs "freshening up". Look at Porsche and 911 World for ads, then start e-mailing your querie.
(Answer by Steve in SLO)
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