6-speed box for 944 Turbo

[944 turbo cabrio]

Hi all,

I know the easy thing to do is to find a 968 LSD boxand install in order to make for closer ratios but thes boxes are hard to find - and when found big money is asked for them :-(

I have a t some time heard that Audi boxes (maybe from the S2?) could also be put in the 944 but I would like to hear in this forum if you know whether it is true - what gearbox exactly is interchangeable for the 944 and also if it works well with the Audi ratios. I expect the chances of finding a used Audi box are much greater than to find a decent 968 box.

All answers highly appreciated


Niels

 

[sawood12]

Not aware of anyone who has actually done it, in the UK at least, but the box does bolt right up no probs. One drive shaft can be carried over from 944 turbo, but the other side is a shorter 968 one. Also the speedo for a 968 is electronic instead of mechanical, so there is a fiddle you need to do to get your speedo working - I think you can pick up off one of the ABS sensors. But other than that I think the install is fairly straight forward.

The real question is why? Apart from them being hard to find and very expensive, the closer ratio's would ruin the turbo drive - you want to exploit the full on-boost part of the rev range and the turbo box's ratio's are perfectly chosen such that when you change gear you're just picking up the lowest part of the rev range so you're not dropping off boost and are right at the start of the boost curve. A 968 box will be lower geared and you'll not be exploiting the full range of boost in between changes. The 968 first gear is a lower ratio so is basically a wasted gear and the 6th gear isn't any higher ratio that a turbo's 5th gear. Also the 968 box has no LSD like later turbo boxes have and i've read that the 968 box is weaker. Not sure if this was a problem with early 968's that was fixed on later models, but there was once reputation with 968's busting boxes.

 

[Lowtimer]

Of course, what breaks gearboxes is not power but torque, and the 944 Turbo, even in standard form, has significantly more torque than the 968. Tuned, of course, it is in a different league altogether. We know that the 944 box was beefed up to cope with the late Turbo engine, but as far as I am aware there is no evidence of the 968 box having a much higher torque rating than it needs for the normally aspirated engine.

I imagine that the 968 Turbo S / RS gearbox was substantially strengthened, does anyone know for sure? With so few cars being made there seems to be little information on them. Wish I could find one of those under a tarpaulin in the back of a garage somewhere though!

I take Scott's point about the ratios - there is no point having a lower bottom gear than the existing Turbo bottom gear and the existing ratios are probably as well choses as they can be for a 5 speed box that has to encompass the speed range of a 944 Turbo.

I do sometimes think that it would be good to have a slightly tighter sequence higher up the box. Second to third in particular is quite a big step and if you spend a lot of time on slowish B roads, as I do, sometimes when overtaking from, say, 40 mph, it would be nice to have a lower third gear. Second is nicely on song at 40 but you only get a short squirt before you run out of revs, while the standard 3rd means from 40 mph you have to go through the spool-up before the car starts pulling hard. It would be fun to try a six speed box which stacks third to sixth into roughly the space occupied by third to fifth at the moment. But not if the price of that is a caravan-towing bottom and second gear.

Of course, a better solution would be Barry Hart's 3.0 turbo, which solves the same problem by a) having more off-boost pull in the first place, thanks to the large capacity, and b) bringing the car fully on boost a lot earlier in the rev range thanks to the extra airflow through the turbo.

 

[sawood12]

Turbocharged engines need a different strategy to N/A cars with regards ratio's. N/A cars have lower torque so get their power from high RPM, so with an N/A car you want a box that keeps you up in the top 1500 RPM, so the higher speed you want to go the more gears you need or you'll need to widen that 1500 rpm band. A turbocharged engine however gets alot of torque right from the lower mid range all the way upto the high RPM range - so about 3krpm range, so double that of an N/A car, so you don't want to be only utilising half that useful rev range by having a box with ratio's too close together.

Apparently german cars boxes had a wider gap between 2nd and 3rd gear due to wanting higher ratio's up the box due to high speed Autobahn cruising, so 1st and second gears were only for getting you going and 3rd to 5th gears were for higher speed cruising.

I personally think the ratio's in the turbo box are perfect. Cruising at 70rpm you're just right at the start of the boost range so have good acceleration from 70mph without having to drop a gear (should you find yourself on a road where you could utilise speeds greater than 70 of course!). 1st gets you off the mark quickly and with some practice and a warm box a slick change to second is possible and from second you can really get going.

Stick to a turbo box and if you have money to burn then throw away the crappy standard LSD and upgrade that. And being controversial, you might want to go to a 220 turbo box and install an LSD. OK, you don't have an oil cooler - but you probably don't need one (Porsche saw fit to chuck away gearbox cooling on the 968 and didn't use it on the Audi S2's) and the oil cooled boxes are 15kg's heavier. The 250 turbo boxes are not stronger than a 220 turbo box, they just had 1st and 2nd gears with harder case hardening on the gear teeth so wear better, but in all my years knocking around on this forum and others i've never ever heard anything to suggest that 220 turbo boxes are prone to failure, they seem just as bullet proof as the 250 boxes, even in modified cars.

 

[Fat Albert]

I had a gearbox go on my tuned SAAB 9000 Aero and had a recon box fitted, turns out they fitted a box from a 2.0 eco instead with much lower gearing and it just destroyed the performance, as soon as it came on boost you had to change gear and lose it all, and then have to spin it up again....obviously they swapped it out for the correct one but it was an interesting experience!

 

[944 turbo cabrio]

Just to explain my wish for closer stacked ratios.
When driving outside the race track I fully agree that the ratios are very well chosen.

However when on track I am very often wishing for something intetween 2nd and 3rd gear as I am running out of ooommmpfff in 2nd and also I am running to low on boost in 3rd to really make the car responsive.

I may better add to the info that the tracks in Denmark all are quite twisty compared to most british tracks.

Cheers from

Niels

 

[sawood12]

the common trick for turbo's on twisty tracks is to install an S2 diff crown wheel. This takes the whole gear ratio stack down a notch or two at the expense of top end - which you don't need on twisty tracks. The ideal thing would be to have two boxes - one with standard ratio's for street and straighter tracks, and one fitted with an S2 crown wheel for the twistier stuff. It only takes about 30 minutes to swap over a gearbox once you've done it a few times so is quite feasible to do between trackdays, or races.

 

[944 man]

ORIGINAL: 944 turbo cabrio

Just to explain my wish for closer stacked ratios.
When driving outside the race track I fully agree that the ratios are very well chosen.

However when on track I am very often wishing for something intetween 2nd and 3rd gear as I am running out of ooommmpfff in 2nd and also I am running to low on boost in 3rd to really make the car responsive.

I may better add to the info that the tracks in Denmark all are quite twisty compared to most british tracks.

Cheers from

Niels

You might consider altering the driven ratio, by increasing or decreasing your cars rolling radius. Given the factors that you have mentioned; Id be looking to decrease the wheels rolling radius, thereby bringing third hear on-boost quicker, for a given speed.


Simon

 

[Neil Haughey]

Remember reading a good few times over the years of guys stateside swapping in the S2 crown wheel. Drops the ratio's down a fair bit but even on fairly long tracks I reckon you have little chance of topping the car out anyway unless running mega power.
Certainly here in the UK 3rd and 4th get very heavily used in an S2.

 

[333pg333]

I can reply on a few levels to this subject. Firstly I am changing to a 968 box. It is to be built up for my racecar in view of having quite a lot of hp/torque. I was very close to using a 996 GT2 trans but eventually chose to go with the 968 one due to the ease of fitting by comparison. I have been going through many mental calculations as to what gearing to go for. Whether to change individual gears or just the crown wheel and pinion. However I also decided to at least wait for the dyno charts before making any hard decisions. There have been people in both camps. As in, some say go for longer gearing to allow the turbo to benefit from boost and possibly torque improvements plus less changing of gears vs others who say that by having the shorter spaced ratios will help the largish turbo spool more readily.

By way of comparison I have been running my 2.5L motor (Gt3076, cam, exhaust etc) with a 951 trans and S2 cwp as mentioned. I definitely feel that this simple modification is a good bang for buck change that brings the car alive. It definitely feels faster to spool the turbo and just more in the meat of the turbo's torque range. For cars that are more focussed as trackday or racers, I think this is a great mod to look at. Especially on short or twisty tracks. Seems good at our longer track Eastern Creek which is probably still pretty short by European standards.
On the track there is the loading of the turbo to consider but more importantly is the ease of attaining rapid rpms.

I have quite a lot of gear charts if anyone wants me to send them. In the end I think that for the system to work most efficiently as a whole you need to marry a lot of items to get the best compromise. As to what you consider a 'tunable item' this is up to each user. For most of us, swapping gears and final drives etc on a regular basis isn't on, so perhaps you need to choose the turbo, cam etc to suit the gearbox rather than the other way around. Well at least it sounds good on paper.....[] The turbo on the 3.1L will be about the size of a GT35 however I will retain the GT3076 if it proves too laggy. Time will tell.

Another advantage of the 968 box over the 951 is that the LSD unit you can fit is larger and there is potential to use a 6 clutch one vs 4 clutch. I am going to try the KAAZ unit.

 

[Neil Haughey]

ORIGINAL: 333pg333

Another advantage of the 968 box over the 951 is that the LSD unit you can fit is larger and there is potential to use a 6 clutch one vs 4 clutch. I am going to try the KAAZ unit.

Another advantage again is its a separate unit so you can swap out the LSD without stripping the whole gearbox apart.

 

[DivineE]

Just to adress the other point I think the audi box that fits is from the audi 100 but besides being extremely rare now it is just the 944 5 speed box without the benefit of toughened gears.

Could be wrong, it was 9 years ago when my lux gearbox failed. I was looking for ways to source a replacement quickly but went with a 944 box in the end.

 

[George Elliott]

Interesting thread, especially the potential in the engine cam and turbo sizing. I guess variable cam timing and variable turbo technology are the modern equivalents.
I know my 951 is crying out for another gear at mid range in 5th.
The crappiest diff in terms of traction that porsche ever provided was an open diff, all my LSD's work well and we have loads of rain to test them. That would amount to over 100k miles of use in various cars. (one car with 145k miles not rebuilt)
I imagine the 968 6speed would have closer ratio's as standard which would help the problem of no-mans-land you describe Niels, when I enquired about this some years ago I was told the torque tube would need to be changed too. The units were big $ back then too.
You might consider a quick spool turbo which would assist the low end pickup in your example where 3rd gear is too high. I have an SPS hybrid which boosts from just over 2000rpm.
The original 911 turbo was a 4 speed [8|], but that was because the box was not big enough to accomodate 5 strong ratio's, bet your glad of 5 cogs now[]
Good luck
George

 

[Mike_Pollock]

2.5 8v N/A 944s have slightly lower 1st 2nd 3rd and 4th gears than the Turbos 16v 2.5s 2.7 N/A and S2 it those ratios could be utilised.

 

[os951]

With a little bit modifications all Audi 01E series boxes can be fitted under 951.Audi version have a similar pick up for speedo like 944 016 series boxes have. Audi used these boxes in most of their applications. There are several different versions available depending the model and engine (petrol or diesel).
Audi 01E boxes were used at least the following models:
RS2
100 late model with 6-speed
A4
A6
A8

None of the Audi version is as strong as 968 version, which is widely sought after by Audi performance people.

 

[944 turbo cabrio]

Thanks for all input.

I will definitely not go down a route with a weakened gearbox -6 gears or not

I am currently only missing to find cheap(ish) pistons for my 2,8 ltr. stroker build - this build will also have 3" exhaust, uprated catalyst, lightened flywheel and pressure plate and a MAF set-up. When the engine is build maybe all problems of ooommfff missing in gears will be a history long gone!? Certainly hope so []

If not, then uprated suspension and bushes + better tires must make me corner faster and thereby getting me into the 3rd gear powerband []

Changing to the S2 cwp is unlikely as I am afraid of ruining the long trip capabilities that I much like outside the track.

@ George: You mention SPS turbo - who is that and is he a 951 specialist?

Best regards to all

Niels

 

[333pg333]

Who said the 968 is a weaker gearbox?? It's not. Many high hp racers switch to the 968 trans so don't be dissuaded by the wrong info. Also there are a lot of Audi gearsets available for the 968 trans.
If you're going to race on big tracks or drive on Autobahns etc the 968 trans will get you pretty close to 200mph in the right car. []

 

[333pg333]

The large Dalek in the middle is the 968 LSD.

 

[TTM]

ORIGINAL: 333pg333
If you're going to race on big tracks or drive on Autobahns etc the 968 trans will get you pretty close to 200mph in the right car. []

200mph with a 968 NA gearbox means 8000rpm...Pure folly!

 

[Lowtimer]

For the fun of it, I have just calculated that if you were to combine a 968 box with the 3.18:1 final drive off a 944 automatic, you would get 29 mph per thousand in top, and would be pulling 6900 rpm at 200 mph.