Porsche Enthusiasts Club Forum

What are the s2 and turbo gearbox ratios.

I assume s2 ratios are shorter?

I have s2 box and an 86 turbo box. Will be fitting a new lsd unit to the gearbox. But wondering which gearbox to use for a race car with between 400 and 500hp.

So strength and ratios to bear in mind.

Cheers
nick

Google it pretty quick top end speed for each gear as well. Iv come across this info a few times

Nick, I have a bunch of gear charts in .pdf format.
If you want to email me via PM's and I can send them to you. On a personal level, we ran our 944turbos with the 5 speed but the shorter S2 Crown wheel & pinion which shortens up the gearbox by something like 15% off the top of my head. It always livened up our cars on the track (and street) but of course it shortens your top speed too. My friend is still using this combination in his 16v turbo and this is a very quick street car that he uses to good effect on the track. I have the 968 6 speed (which I don't like as much as my old 5 speed) but it seems to work pretty well in terms of gearing. It's not dissimilar in ratio to the 5 speed / S2 combo and is shorter than a lot of people thought would be suited for a 500+ whp motor, but I can't complain about the actual ratios.

Cheers

Patrick

Cheers. What sort of top speed will the s2 ratios provide? With a rev limit of approx 7500rpm as a guide.

Any differences in strength between an s2 and turbo box?

Regards
nick

The 951 turbo S gearbox is the strongest.
I have the S2 gearbox on my GTS wannabe car, running @1bar from a K27...i drive it fast sometimes, but its a road car so only a bit of abuse.
I'm not sure how much abuse the S2 gearbox will take before giving up...but for a race car..maybe go for 951S gearbox.

Gear ratios are shorter on the S2 than the Turbo S..but seem bang on for 250-300hp..might be too short for 400-500hp
I had the 944NA gearbox on my car for a while and it was too short, it also got destroyed in a couple of years of ocasional WOT.

Top speeds are relative to wheel diameter....but here is an example:

With a 225/45/17 new tire the 083F gearbox (944 S2) will give just shy of 300km/h at 7500RPM in 5th gear
At 5000RPM with this exact setup you will do 200km/h
6500 RPM will do for just shy of 260 km/h

4th gear at 5000PRM will do 160km/h

thanks morghen. some good info.

tbh if an s2 box is up to the abuse then 300kph is plenty as thats nearly 190mph.

if my 86 turbo box is stronger than the s2 box, then maybe the best option is to steal the final drive from the s2 box and put it into the turbo box.

this will be used purely on race track

cheers
nick

Your 86 turbo gearbox is not a turbo S gearbox. If i'm not mistaken, the turbo S was only offered starting with 1988.

Correct, a proper turbo s box has hardened 1st and 2nd gears, lsd and oil cooler as standard. Your 86 box may have the oil cooler loop and lsd but will not have the hardened 1st and 2nd gears.

Stuart

i never said it was!

i have a turbo box and an s2 box in stock, so i will try them out and see how they perform rather than sourcing a turbo s box which are silly money! prob £1500+ and it will have an old tired lsd fitted.

i can use one of my boxes in stock, and fit a brand new quaife lsd unit for £800.

if it breaks, will think of another option, but i would say the boxes are much stronger than people realise. i know of a few cases of people using lux boxes on the back of turbo lumps with 350+bhp, and patrick above says he has used a few different options with over 500bhp so im not going to spend a fortune on a turbo s box when the boxes i already have will most likely be up to the job.

was mainly asking about ratios, and if my turbo box was any stronger than my s2 box? if the only gain in an s box is hardened first and second gears than in my opinion its not worth the outlay. as the car wont see much of 1st and 2nd gear when going round track, and tbh i could even have the whole gearset in my turbo/s2 box cyro treated/hardened etc for likely less than the cost of a turbo s box anyway.

regards
nick

If it helps I managed to break the torque tube flange without damaging the s2 box in mine, whilst getting used to the springless paddle clutch I had. Box is still going strong.

Much rather the torque tube broke than the box so thats a good sign lol. Torque tubes are ten a penny.

I do have a paddle clutch so might need to be careful on launches!

I have 3 torque tubes so some spares in stock lol

nick

Thats a good thing that the coupler goes first. I crunched the 944NA gearbox in 3rd while WOT on a climb.
However changing the torque tube is not a funny job, you also have to check and realign the rears as you have to take the torsion bar beam down to replace the tube.

Sorry I have been out of touch and haven't replied to this. I've got a bunch of charts at home which will show you exactly what speeds you'd get with various different gearboxes and some different final drive ratios as per changing the crown wheel & pinion. We ran our turbo 5 speed boxes with the S2 ring and pinion for some years and in fact my friend Sean Buchanan still runs this setup in his 3Ltr 16v turbo to great effect. His car would have over 500bhp and really doesn't suffer by having the shorter final drive ratio. Not sure how long your straights are Nick but I'd think 300kmh with this setup might be outside the realms of possibility. Perhaps a very custom motor with lightened internals might allow you the rpms to get there? I currently run the 968 6 speed which has similar ratios to the 5 speed with S2 r&p for the first 4 and maybe 5 years from memory. The 6 speed is probably stronger due to larger differential and r&p but I actually preferred the 5 speed in terms of shifting.

I'd be inclined to try the 5 speed with the S2 r&p Nick and go from there. It's easy enough to provide better cooling to the non S 5 speed and I would run an aftermarket LSD rather than the stock unit for a racing application. So as you say, the hardened 1st and 2nd isn't a deal breaker in my books either. I also invested in some very expensive aftermarket CVs and axles through Lindsey Racing. Something like $1200 before shipping. We've put 554hp at the wheels through these and so far so good but some might say just stay with stock and leave them as a fuse.