993 transmission choices

[Bill Verburg]

stock g50/20 used on '94-98 US and '97-98 RoW



g50/21 used on RoW 993 '94-96


g50/30 used on 993Cup/Supercup


g50/31 used on 993RS


g50/32 used on 993RS/CS

[AC993C2S]

I recall the first time I took off from a start with my new box, and these charts reminded me of how tall that first gear is...45mph!

Great comparison/resource here.

[aigel]

g50/31 for me please. That first to second drop is a joke on the stock US box.

George

[kang]

Good reference material, thanks Bill.

[Ag02M5]

Hey Bill.

Is this a program that is available? I'd like to play with the gearing for my turbo.

Cheers.

RT

[Michel J]

How much $ for a G50/30? Who can regear my G50/20 and for how much? I know it won't be cheap.

I agree with George re the 1st to 2nd transition having quite a drop in RPM.

I have been driving my 95 993 for a month and love it. Big change from my 76 911S

Cheers,

Michel

[Bill Verburg]

Originally Posted by Michel J

How much $ for a G50/30? Who can regear my G50/20 and for how much? I know it won't be cheap.

I agree with George re the 1st to 2nd transition having quite a drop in RPM.

I have been driving my 95 993 for a month and love it. Big change from my 76 911S

Cheers,

Michel

the /30 will only be available form someone parting out a 993Cupcar
/32 & /31 are available throught the dealers, last price i heard for a /32 was ~$15k, /31 is roughly 1/2 that

Paul guard has or can get all the gears, depending on the trans you have 1 & 2 changes will require a new mainshaft

No it's not gonna be cheap

[Tom W]

The rpm drop from 1st to 2nd is not an issue when racing as you never see first gear unless you are pulling out of the pits. In most cases, it makes no real difference as you accelerate so fast in those gears anyway. You gain speed and lower lap times the most by doing the high-speed turns better/faster and not worrying about a 1 mph difference in the slowest turns. What matters most is how your 3rd and 4th are geared as they are the gears you use the most. It will not help if you go to shorter gears but then find that you run out of gear before most braking zones (and it's too late in the straight to waste another 0.8 seconds shifting).

For example, I chose a /32 due to the steel synchros and I thought the gears might be a bit taller than I wanted, but since I was also going to remove about 300 lbs from the car, I thought it would be ok. The power/torque curves for my car indicate that I should shift at about 6500 rpm (even though I could rev to 8000 and have the rev limiter set to 7400). I chose the gears based on an analysis of speed at the end of the straights, mid apex speed and corner exit speed at the two tracks I drive the most (Thunderhill and Sears Point). I wanted to ensure I would be in the power at mid apex and not have to shift before corner exit. I found that I'm at the top of 4th (ie 6500 rpm) in 3 spots where it's too late to shift to 5th. However, since I have the ability, I still accelerate until 7000 or 7200 before I hit the braking point. IN this case the /32 is almost too short, but the flexibility my engine provides overcomes it.

My point is that it's not as simple as dropping a thigh ratio box into your car and going faster as a result. You have to look at the tracks you run, how you drive and what your car needs as a package. It's a lot of money to spend, especially if you get it wrong.

[Bill Verburg]

Lower & Closer is certainly not a panacea to all situations, it just makes the probability of being closer to the ratio you want for the widest possible range of situations. It would be wonderful to regear for the optimum setup at each track(or street situation), but that ain't gonna happen for us mortals.

6 choices spread over 165mph range will always be closer to optimal than 6 spread over 185mph range. The worst thing about lower gearing is the danger of being too low in first and sixth. Too low first makes the gear unusable except to get rolling(think truck low range gearing), too low in 6 makes the cruising revs too high for those of us w/ dual use cars.

The second worst thing is the danger of having drops w/ inappropriate spacing.

My favorite saying "It's all a compromise"

[Ag02M5]

Originally Posted by Ag02M5

Hey Bill.

Is this a program that is available? I'd like to play with the gearing for my turbo.

Cheers.

RT

I think my question got missed.

[Bill Verburg]

A potential regear for a stock /20

[Matt Monson]

When doing that stock 5th gear into 6th position stack I usually like to go a tick or two higher than that on both 4th and 5th gears. Something like a 1.063 or 1.040 5th and a 1.250 or 1.286 in 4th. The issue is that unless the car has got a peakier cam or a fair bit more horsepower than stock, trying to keep accelerating at 130mph on the 5-6 shift it's just a bit more responsive if you are entering 6th with less than 1000rpms drop.

[Bill Verburg]

Originally Posted by Matt Monson

When doing that stock 5th gear into 6th position stack I usually like to go a tick or two higher than that on both 4th and 5th gears. Something like a 1.063 or 1.040 5th and a 1.250 or 1.286 in 4th. The issue is that unless the car has got a peakier cam or a fair bit more horsepower than stock, trying to keep accelerating at 130mph on the 5-6 shift it's just a bit more responsive if you are entering 6th with less than 1000rpms drop.

That's what a friend did w/ his

[aigel]

Originally Posted by Ag02M5

Hey Bill.

Is this a program that is available? I'd like to play with the gearing for my turbo.

Cheers.

RT

It appears to be a fairly basic excel spreadsheet.

George

[Bill Verburg]

Originally Posted by aigel

It appears to be a fairly basic excel spreadsheet.

George

yes, very basic i'm sure that you could whip one up in a few seconds

[Matt Monson]

[Bill Verburg]

a couple more

change cwp,1,2, stock 3,4,5,6


change 3,4,5, stock 1,2,6

[Matt Monson]

Originally Posted by Bill Verburg

a couple more

change cwp,1,2, stock 3,4,5,6

I just can't see why these days anyone would put that kind of money into a G50/20. For the same $8000-$9000 that build is going to run someone in parts and labor you can find a GT3 G96/90 gearbox and get an inspect and reseal on it, and get an LSD to boot. Or if you shop right you can even find a G96/96 with a cooler for that kind of money. And both of them give you the beefier ring and pinion.

Availability of these core GT3 boxes has gotten so good that it just doesn't make sense to put more than $4000-5000 into a G50/20, assuming that you already own the gearbox as a core to build on. If you've actually got to go out and buy a G50/20 core AND build it up, it makes no sense to me at all.

For comparison, the G96/90 ratios are as follows:
9:31 R/P
11:42
20:43
25:39
33:40
37:36
39:32

If you chart it, 1,2,3 give similar numbers to the above referenced chart and then on 4,5,6 the gap opens up a bit. Even if you buy a shorter 4th and 5th for the GT3 box and are into it for $10,000 that's a lot more gearbox than the same money buys you in a G50/20.

[Bill Verburg]

Originally Posted by Matt Monson

I just can't see why these days anyone would put that kind of money into a G50/20. For the same $8000-$9000 that build is going to run someone in parts and labor you can find a GT3 G96/90 gearbox and get an inspect and reseal on it, and get an LSD to boot. Or if you shop right you can even find a G96/96 with a cooler for that kind of money. And both of them give you the beefier ring and pinion.

Availability of these core GT3 boxes has gotten so good that it just doesn't make sense to put more than $4000-5000 into a G50/20, assuming that you already own the gearbox as a core to build on. If you've actually got to go out and buy a G50/20 core AND build it up, it makes no sense to me at all.

For comparison, the G96/90 ratios are as follows:
9:31 R/P
11:42
20:43
25:39
33:40
37:36
39:32

If you chart it, 1,2,3 give similar numbers to the above referenced chart and then on 4,5,6 the gap opens up a bit. Even if you buy a shorter 4th and 5th for the GT3 box and are into it for $10,000 that's a lot more gearbox than the same money buys you in a G50/20.

Matt, I used to say the same until it was pointed out to me(I think by Chris Cervelli, but my memeory is failing rapidly) that there are some major physical differences that are issues. I know that from ~2002 they went to cable shifters as one issue but for the life of me I cannot remember where the response is or the details. Do you have any input.

Here' a 1999 996Cup trans that I looked at as one of the closest to being useable in a 993

[Matt Monson]

Bill,
You're right. I shouldn't really glaze over the cable shift part of it without accounting for the cost. The conversion can be done with components from Brandwood for just shy of $1000, so that does need to be factored into the cost of going the GT3 route in a 993.

The cup gearing would be fabulous on a 993 street rod. I feel that any time you go taller than 3.00 on first gear in the 993's you are just stressing the system too much if it's a street car. On a track car it doesn't matter so much, but for anyone who's got to deal with stoplights and stopsigns, it's a pain. The cup's 3.154 1st is a good balance point.