[akeric]

So basically I am finishing up my turbo build and need to select a clutch. I know that a stock sti loses about 20% of its power through the drivetrain from crank to wheel. 300 crank hp / 300 crank tq, and they dyno 240 / 240 or something like that at the wheel.... right. So when selecting a clutch based on a 'projected' wheel torque is 20% going to be how much I am losing? I don't really see how that is possible.

If I'm losing 70hp (or tq) from crank to wheel at stock power levels how is doubling my power level at the crank going to double the loss of power through the drive train (assuming no drive train modifications). I can see how additional power might increase power loss through the drive train a bit maybe going from 70hp at stock levels to 80 or 85 but doubling it seems a bit of a stretch.

I guess the reason I am obsessing about it is simply I don't want to buy more clutch than I need, not that I mind spending the money on a quality item why buy a harsher clutch than you need?

Does anyone have a good method for figuring how much torque your making at the crank based on the wheel figures? (besides a engine dyno )

Thanks for the help

 

[07EVOK1LR]

only what you have already mentioned, I tend to use 17.5 percent but i like things to be difficult

in this case where you want to side high just use 15 percent so 400 wheel tranlates to 470 crank/flywheel hp for example and dont forget clutch is tq so assuming your hp and tq are equal

 

[akeric]

only what you have already mentioned, I tend to use 17.5 percent but i like things to be difficult

in this case where you want to side high just use 15 percent so 400 wheel tranlates to 470 crank/flywheel hp for example and dont forget clutch is tq so assuming your hp and tq are equal

Yeah I am aware of the clutch holding tq not hp but I am assuming equal amounts. I just wanted to be sure that I really needed a clutch that would hold 625tq if I was shooting for 500wtq. That pretty much limits me to a 6puck ceramic clutch.... I would have have some other options for smoother engagement. I don't do alot of traffic driving but there is some. Plus I would rather overshoot a bit....so I'd really be looking at a 679tq clutch (ACT 6puck sprung center w/ HD pressure plate)

I guess I just have a problem losing over 100hp through my drivetrain....lol

 

[USNSTI]

You are totally overthinking this. The 20% is an estimate. There is no real way to figure it out exactly. You would have to use some kind of formula based on variables that are difficult to measure. Just use the 20% and round up so you can be safe. Or if you don't agree with that number then lower it. Again it's an estimate.

 

[akeric]

You are totally overthinking this. The 20% is an estimate. There is no real way to figure it out exactly. You would have to use some kind of formula based on variables that are difficult to measure. Just use the 20% and round up so you can be safe. Or if you don't agree with that number then lower it. Again it's an estimate.

I was only curious if the 20% loss estimate was independant of how much power your making or not. Or rather if it was fixed.

 

[USNSTI]

Theoretically it would go down slightly as your power increased. But really there hasn't been a whole lot of testing done on this. People just took the OEM 300 and compared it to what they saw on a dyno. Lot's of room for error in that kind of calculation. That's why most people just go with 20% across the board. Err on the side of caution basically.