Hi,
Anyone knows the limit for this manual gearbox/drivetrain (not clutch)? What will break first?


Thanks

 

I don't think you have to worry unless you're willing to put &15k+ into turbocharging it. There's been guys running TPC and Vortech forced induction for years now.

Bisi was running 900hp+ on his turbocharged NA m96 with stock gear box IIRC. I'm not sure how long that lasted though.

Considering the NA m96 only tops out close to 280tq with all bolt ons, there's a lot of cushion in there.

 

You should design your setup such that the clutch does go first before you shred internals.

 

Thanks for the replys.
I will use a clutch that will hold the tq +more. Just would be nice to know when gearbox usually breaks, and limit tq to a little lower.
Which gear usually strips teeths?

 

Reverse.

 

Well I am not concerned about breaking reverse


Anyone knows what normally breaks first and at what tq? I supppose the C4 gearbox are alot weaker than TT...

 

From just high torque the input shaft. It can fail at any time even with a stock engine if the car is launched hard.

Roughly figure about a 1.5 margin. Bump the torque by 1.5 times over stock and you are probably close to the limits of the transmission. It won't last forever at 1.49 times over stock nor immediately explode at 1.51 times over stock but it is close to its design limit and has used up all its nominal margin. There are enough differences between transmissions one might last and last even fed 1.5 times the torque it was expected to handle with a stock engine but most will not.

The Turbo 6-speed manual is heavier duty than the NA 6-speed but I don't know exactly what are the differences. The Turbo transmission has to deal with 420hp and 413lb ft of torque while the NA 996 engine delivers 315hp (2002 and later IIRC) and 273 lb-ft of torque.

But maybe the C4 -- to accommodate the AWD -- uses the Turbo 6-speed? It shares the brakes and suspension with the Turbo.

 

The stock c 4 transmission will work up to about 600 ft lb area with an upgraded clutch with power adders like supercharging/turbos. its not the HP # that counts it is the torque number that decides it. that is why you see some folks add a turbo or supercharger, then remove the cardan drive shaft, or 4 wheel system all together. because the thought is the front diff cant take anything other than stock engine torque and it makes the car lighter.

 

There are multiple LS swapped C4 cars. So the trans can handle at least 400ft-lb at the wheels.

 

600 ft lb is fine. Yes that is why I asked for tq not hp. Alot of people believes it is hp that destroys gearboxes.
Is the front diff really that weak?
Thanks

 

Is the front diff really that weak?

the small size is what i think helps some folks think it cant handle anything over stock tq. i dont believe that line of thought,the axles would give out before the diff in my opinion.

 

Well, it only gets at most 40% of the engine's torque -- and for the Turbo this 40% number is obtained at around 150mph -- so it doesn't get subjected to big loads and even when it does get subjected to the max load it doesn't have to handle much thus it can be smaller, lighter.

The front axles won't give out though before the diff. Actually what will likely give out first is the viscous coupling. There is a limit to how much torque the viscous coupling can transmit -- the torque is being transferred by viscous fluid (with a working temperature of IIRC around 350F!) -- and this I believe is the weakest part of the front diff assembly.

 

Thanks

 

Typically hard launches, quick hard shifts, and wheel hop destroy transmissions quickly. unless you are making large power numbers, the deciding life factor of a mechanically sound transmission is the user and treatment of the unit. I typically break transmissions under hard shifts , damage clutches with hard high rev launches, and break all sorts of stuff with bad wheel hop. There are no real power numbers for this.