xviper

I was bs'ing with a friend about drag racing, etc. He's a hot rodder from way back. He says that many guys will torque load the car's power train before they dump the clutch. This means that, while stopped, they slightly engage the clutch to take out all the slack in the power train from aft of the clutch to the tires. This eliminates all the tiny little spaces that exist between each cog and gear. If you add up all the little spaces it's like one big gap. He says it's a lot easier on the tranny, drive shaft, diff if you don't "hammer" on the power through all those little gaps.
Have you seen those desk top toys where there are about 5-6 silver balls hanging from strings? If you slam the 1st ball into the bunch, the force is transfered through all the middle balls (they don't move) and only the last one bounces. But if you were to re-suspend the balls such that there is a small gap between each one and you slam the first ball, they all move that little bit. So you can see that it's a lot easier on the middle balls (your drive train) if there were no gaps.
I'm curious to hear from those who do hi rpm clutch dumps and have had breakages such as diffs, etc, if you torque load your powertrain first or not. And does everyone think about this concept?

RandyP

The clutch disk has springs in it to minimize this shock.

Penforhire

I think it would be a good idea, if we didn't have such a wussy clutch. As it is you need every bit of engagement to avoid spinning it (dreaded burning smell to follow). If you slip it a little just before dumping I imagine it only makes such a spin more likely.

Quick96

He said Balls (in Buttheads voice)

s2ktaxi

Most of my clutch drops are done at about 3000-4000 rpm on a lower than average traction surface at autocrosses. This is a lot easier on the clutch that a regular slightly slipped clutch launch at your normal 1000-2000 rpm on a higher friction surface.

Jason Saini

Having done over 800 6K+ drops for this past season's autocross season, I can say that with the stock clutch that is impossible. If you engage it at all, there is too much risk of slipping it. The only way to get the tires spinning without slipping (consistently) is to shock the rear tires as hard as possible.

One thing that we have considered doing is narrowing up our ring & pinion gear lash to keep that gap as small as possible. This is the weak point of the drivetrain, so I think that it's the gap that matters most. By putting the lash at the narrowest point of the adjustment range, we will be putting less strain on our R&P. We'll have the rear-end apart soon and can report on how a season of racing stress treated it.

xviper

Some of you might be misunderstanding what I mean by torque loading. You engage the clutch only enough to take the slack out of the drive train. Once done, you would push the clutch back to the floor before your usual launch. As long as you don't roll forward, the drive train maintains its no "slack" condition.

Jason Saini

OHHHH.... I get it... yes, I do that. When we do the launch, we have to stage which means pulling slowly into the lights. Also, I'm hitting the brake while creeping forward, which takes all the slack out of the drivetrain. I thought you meant letting the clutch out a little, then popping it out all the way. I understand what you mean, and it's a worthwile technique.

KeithD

Jason,

Did you do those 800+ 6k RPM clutch dumps with a stock clutch and stock pressure plate?

Just curious...

Penforhire

Keith, of course he did. He's a respected racer in A- STOCK class, which doesn't allow any clutch mods.