[MikeyB]

Hi all, my 03 WRX is running 330 BHP with a VF34 turbo, and has an Exedy single plate racing clutch installed.

I’m meeting up with my mate soon who is running 360BHP in a MR2 turbo and we are going to have a couple of drag’s down the strip.

What I’m wanting to know is, what technique (considering the clutch and gearbox) is best to get away from the line… I’ve tried everything but totally dropping the clutch as I don’t want to f*ck the gearbox up?

If I don’t launch quiet right, the whole car shudders violently, even if I change from first to second not quite right the whole car shudders again…

What am I doing wrong??

Cheers, MikeyB

PeteBrant

At the point in your rev range that has maximum torque. Assuming you have had it dyno'd look on the print out to see where this point is - typically around 4000rpm - torque then begins to tail off after this point, so anything above this will not get you off the line as quick (obviously there is a tolerance on this, 4500rpm will be fine - you just won't gain anything launching at 6000rpm, infact you will be slower) . When changing gear you want to be changing into the powerband and before the power in you current gear tails off, so at around 6500 revs, change gear. Obviously this takes knowlege of your own car, but you want to be changing gear before the horsepower tails off, again, there is nothing to be gained from being in a gear past the max HP point.

Remember power for speed, torque for acceleration.

Assuming your gearbox and clutch are built to take the horsepower/torque then the wheels should break traction before the gearbox/clutch does. So dumping the clutch at 4000 *should* be ok.


That's all th theory anyway. I am sure people who regularly do 1/4 miles runs will have far more knowledge than I.

[MikeyB]

Cheers Pete, great advice.

Here's the dyno's for my car after the engine build.



What's the violent judder all about then when I get it wrong?

WHEELSHOP0_0

Could be something loose, or your clutch protesting too much or possibly axle tramp if you get violent wheelspin(very unusual in a Scoob)
Do you have someone who can view from the outside as to what the car is doing at that point as your concentration will be elsewhere, or get it on video, if your wheels "tramp" up and down as well as spin this is a prob.

If you have had a clutch replaced did they skim/replace the flywheel when it was done I have heard this can be a problem on some models.


Hope this helps

PeteBrant

Sorry mate - can't see the picture at work. As for the judder, one can only assume it is clutch related - as to why or what to do about is difficult to say. Does it alwasy judder? or just when cold?

[MikeyB]

I can get it to judder when I want, if I get the clutch 'right' then there's no judder, I just thought this were characteristics of a single plate race clutch.

I bought the Exedy lightened flywheel at the same time as the clutch and engine rebuild etc...

Rcomms

I would think that the juddering is clutch related tbh. If i want to launch quick (rarely!!), I set just over 4K and drop the clutch. Works sooooo well its untrue. very little wheel scrabling, it just seems to grip and go. I never changed above 6.5K either, in any situation!

WHEELSHOP0_0

The only juddering I got from my semi race clutch(AP triple organic) was at low revs never when loading it up with revs, but I dont know about this situation anybody else got one of these clutches?

[MikeyB]

Will the gearbox in the car take a launch at 4k? Will the clutch take all the stress off the gearbox?

[MikeyB]

I went out last night at around 11pm, found a very quiet back road near an industrial estate and had a few attempts at launching.

It was dark, misty and very damp.

I got the revs upto 4,500rpm and dropped the clutch. (not side-stepping, just dropping it)

WOW, what a noise!! The car didn't actually move, (only about a foot) as all four wheels where breaking traction, then it finally found some, off I went!

Tried this a few times but the conditions were just crap so I could only spin the wheels every time.

The tyres are middle range as they came with the alloys, but I'll be putting the T1-R's on asap and will try again.

Can't wait to give this ago in the dry!!!