333pg333

So I've decided to go down the 968 trans route and am getting one built up to suit my trackcar. Without dyno charts just yet and realising that gearing is very subjective based on each track, I'm just wondering on a few issues that I am going to deal with.

So from what I gather, many people who change to a 968 trans also change the gears (mostly 4th through to 6th). I believe this is because the stock gearing is a bit too short for a higher output often larger capacity boosted motor. Refer to the charts shown. You can see on one of the charts a 951 trans with an S2 ring and pinion. This is what I currently have been using with my 2.5L motor that would produce 330whp to 350whp on many dynos. It actually suits my setup and the track that I mostly run at. The stock 968 gearing is very similar up to 5th so having an extra gear is nice...but the incoming motor will have significant differences.
My feeling is the longer the space between gearing, the more torque will develop? Then it becomes a matter of driving the car on torque rather than rpms. I don't mind this in theory but just not sure if it's the best thing under the circumstances. On one hand if I'm going to the trouble of having a modified trans built and shipped then shouldn't I get as much done in the first place...or do I wing it with the stock gears and suck it and see?

Also will the longer gearing put more strain on the driveline components due to the longer load under higher torque?

It's been recommended that I look at having some of the internals REM'd and / or Cryo'd. However there's a caveat in that the REM process can be detrimental to the article if not done properly so does anyone have a recommendation of a shop that they 100% trust? Roger at CMS who is building the trans says he no longer has and has warned me to be certain of the shop's credentials for the REM procedure.
http://www.rosler.us/north-america/s...m-process.html

So what other things should I consider? I'm looking at these billet plates for the casing to add reinforcement.

Van

Are you just super wealthy or something?

If the S2/951 hybrid is working for you, stick with it, I say. Put your money elsewhere.

333pg333

Why of course. I'm the King of Australia!! No just spending my retirement fund Van.

The reason that I'm changing is due to the new motor Van. It will have significantly more power than the current one. The short geared trans I have now won't suit it, hence the questions.

George D

Patrick, drive the car as stock, then make any decisions. A stock 968 Six speed will hit 191 at 7100RPM. They are G50 transmissions, and you can get whatever gears you want. I would also recommedn that you change to a 968 bellhousing. Two hour clutch jobs if worth the money. You will have to do some exhaust mods, but it's just cutting/welding.

V2Rocket

how do you guys deal with all the blood rushing to your head, being upside down so long

Thom

If anything try to get a R&P made in the 3.400 size of the original 968 TS unit.

piperporsche180944

Based on the chart, the 4th gear ratio in is more favorable in the 968 gear box. On a dyno run wouldn't that net a higher rear wheel horsepower rating using the 968 transaxle since most dyno pulls are done in 4th?

Id go with a stock 968 gear box simply because you have more fun gears.

m73m95

They are G44's not G50's.

I've been doing a LOT of research on transmissions for the last week or so, and I've talked to quite a few transmission shops that deal with ZF stuff. Nearly all of them said that a 951 box is better for a track car, and to use the 968 box for the street. The 968 box has very weak syncros, and to either upgrade them, or use a different gearset with straight cut (no syncros) would cost more than the transaxle itself. The 951 box is plenty strong enough, has MUCH better syncros, and is geared more toward track use.

333pg333

George it's not the top speed I'm concerned about. It's the gap between the gearing being most suited to a larger motor and also of where it's going to hit redline on the track that I frequent the most. I don't want to have to change into 6th gear just before a corner if I have to change back down again.
Also I'm pretty sure the 968 box isn't a G50. I don't even think you can interchange gearsets with 911s but I might be wrong. Having said that it turns out that there might be many brands of cars that used these transmissions and buying r/ps and gears for a e.g. Citroen vs a Porsche will be a lot cheaper.
Thanks Thom. Possibly a good idea and I hadn't thought of that.
I'll have to compare against the stock 968 gears.
The other thing I'm wondering is just about having gearing spaced wider than stock to take advantage of more torque and boost, or using the stock 968 gearing which might be termed a close ratio box for this application?
My current setup with a smaller motor and shorter gearing worked well but it involved quite a bit of gear shifting. In terms of enjoyment this doesn't phase me, but in terms of time it is clearly better not to have to change gears as often. I would think with more widely spaced ratios as opposed to just changing over the ring and pinion might be the best of options. I will wait for the dyno charts and probably make my decision based off these.

333pg333

Just to clarify. The choice isn't between a stock 951 and a stock 968 trans. I am going to use a 968 tranny but am trying to decide what changes (if any) are to be made to the gearing. I'm going to have the 968 box reinforced and possibly have the gears treated for longevity. (REM &/or cryo).

anders44

what happend to your 996 turbo tranny?

I'm just going to try to run a few stock 951 units, I currently have 6, if they all die.. Im in the think tank again.

m73m95

I don't think there needs to be anything done to improve actual strength. The biggest concern with everyone I talked to was the syncros. Improve those, and you should be good to go.

California Motorsports has different gear sets to choose from, or they can custom grind you a set if you want too..... Speed costs money. How fast can you afford to go?

333pg333

It's not merely a matter of extra tensile strength, it's also trying to increase longevity through minimising friction. That's where I'm looking at REM. Perhaps it's being excessive but when you get charged the prices down here to repair, replace, or refurbish, and also just reducing down time, it all makes sense.
In terms of adding or reinforcing the case with the billet plates shown in my first post, there must be a reason for these to exist and I don't believe it's merely a money making process.
The GT3 guys change out their syncros to s/steel so this could be an option as well.

DFASTEST951

I found the answer. See my new thread about the 968 gearbox options we now have.

Thom

If you already spend much time shifting on your 2.5 with the S2 R&P you will be in for even worse gearknob thrashing with the 968 NA gearing on a 3.0 motor aimed to make 500+ lbs.ft.
As you can see from the graph I posted the 968 gearbox gets you about the same first 3 gears as the 951 trans and shorter 4th and 5th. The 6th is here merely for economical motorway cruising, and the occasional high speed adrenalin rush (on private roads of course).

I also looked into more widely-spaced ratios on the 968 gearbox using different combinations of gears from the FWD 01E VAG parts bin, but couldn't find a set up with ratios that were evenly-spaced enough until I came up with the possibility of a 6 speed gearbox with about the same first 5 gears of the 951 trans and a monster long sixth - with the stock trans I already have problem keeping the car on the ground above 150mph, I almost coughed at the idea of taking the car well over 200mph...

Though the factory 968 TRS cars made with 968 NA gearing they had "only" 368 lbs.ft and at best 350bhp to deal with, and I'm sure you are looking at quite more than this with your new engine.

Replicating the 968 TS trans is IMO the best thing to do. At least I think this would be the best gearing for my own engine.