333pg333

Do you base this on the shortened final drive Adam?

gt37vgt

yeh the road has 15% less mechanical advantage on the gear box and the gearbox has 15% more mechanical advantage on the half shafts . so max torque at the gear box is the same but you only are use 60% max torque to waste a wrx when it would need 80% of max torque in a 951 box .
so if you and i were accelerating side by side at the same rate say .7G with the same torque at the tires you would be feeding less torque (more rpm) to the crown wheel than me .

Oddjob

If your mechanic is who Im thinking, I tried to tell him right here on rennlist that the S R/P would not last in a Turbo. He made the claim that it was stronger than the S2 and Turbo, unfortunately he found out the hard way that was not the case.

Oddjob

An S2 R/P in a Turbo trans, assuming the 0.829 Turbo 5th gear, will redline (6500) around 148mph with stock diameter rear tires.

An S2 trans with the S2 5th gear(0.778) is pretty close to 158 mph at 6500.

333pg333

Pm sent.

333pg333

Without doing the maths, I would suspect you lose at least 15mph just by seat of the pants dyno. I am OK with the 5 speed / S2 for the most part. Ideally I will look to the 6 speed plus upgraded axles and CV's at least. Unfortunately I think these upgrades will transfer more load to the gearbox, but what do you do?

gt37vgt

i looked it up the 968 box has shorter diff ratio similar to the S2 and the 6th gear is kind of like the final drive of the 951 set up i think the i would be really happy if I could have 30% taller 1st and 2nd in any box

Oddjob

Well, assuming 1-4th gear, where the gears are the same regardless of S2 or Turbo Trans, the torque from the engine through the input shaft, gear sets, bearings and pinion gear would be the same. The difference in mechanical advantage is the R/P ratio (which is the torque mulitiplier), so the only components within the trans that feel a different load due to the different R/P would be the differential housing; the diff bearings and case side plates really only see thrust loads which are not necessarily directly proportional to the shaft torque. So Im not sure how the Turbo trans would be more prone to internal failure than an S2 trans? I agree that the CVs are feeling the 15% higher torque - and that will reduce their life, especially if you are running significantly higher power than stock.

I have a full S2 trans in my street/DE car. Because of the relatively tame use, I have not worried about breaking anything. Also, I intentionally kept the S2 5th because I didnt want the motor buzzing on the highway in 5th; and when I run that car on my home track, I would get close to redline with the short 5th going through turn 1, so I wanted to leave myself and the car a few hundred more rpms by sticking with the taller S2 5th. If I ever change my mind, I have the 0.829 gear set sitting on the shelf.

Unfortunately, I have to run the standard gearing in my track/race car, per the rules class.

Do you guys know the gear mfg company that makes aftermarket and custom gear sets in Australia - they supply Powerhaus II. Not sure if its the same company, but someone down there is also making the LSDs similiar to the Guard units (if not the same...)?

333pg333

When I had approx. 280hp I found that the stock 951 gearing was too long especially in 1st and 2nd at times. If we have higher power, say 600+ is that going to be diminished?

gt37vgt

yeh pat has one give it up Pat.
only first gear is the same .across the board. and do you know were i could get taller 1st and 2nd gears made.???

gt37vgt

I don't find the 951 gearing too tall at all i can just break traction in third as it hits full boost (22) at 3400rpm no clutch dumping or such i would think my car would be around 340 odd hp

333pg333

To both of your questions re custom gearsets, yes I do know and so do you Adam. They are made at Mondena in Melbourne. Jim they make product for Guards, Quaife, Ferrari amongst others. We use their custom LSD's. I believe that JET951 still has one in stock too. Interestingly the one for the 968 is quite a bit larger.

333pg333

You adapt to what you have. If you drove my car you would see the difference. Like a rally close ratio box.

Oddjob

Sorry Keith, nothing pointed at you, but that information is not correct. The reason to install the S2 R/P in the Turbo or Turbo S trans is because of the shorter final drive/faster acceleration. It is strong enough, but it is not stronger.

The ring gears are the same diameter, the Turbo has 27 teeth on it, the S2 has 31 teeth on it. Therefore the S2 gear teeth are smaller (and weaker), by approximately the same 15% difference in ratio. The pinions both have 8 teeth, but the Turbo pinion is larger in diameter and therefore the teeth are larger-beefier. I cannot understand how anyone that has looked at both components side by side, and has any basic metallurgy/engineering sense, could conclude anything other than the Turbo R/P is stronger.

gt37vgt

sweeet I'll fly up next week get a spare set of tires and a full tank of homebrew