OzzyTom

Hi guys... just want some feedback as to whether this is a typical issue that anyone has experienced, or whether I may have some other problem ....

Motor is a 475hp 383, 10.3:1 static comp with a manual 5sp box (TKO600)

Hard accelleration in 2nd gear to ~ 5800, as I lifted throttle I detected the rear wheels momentarily locked up before engine rpm followed axle speed on decelleration.

rear wheel squeal was momentary, but detectable. This on a dry bitumen straight road surface.

I've never experienced that under engine braking alone....
Is this typical ??

I'm thinking on a greasy surface it could provide a bigger surprise

AU N EGL

are you blipping the throttle to rev match on decel?

RAFTeRACER

Your wheels likely didnt lockup, they were just not mooving as fast as the car for a moment. Happens all the time, but you usally dont hear it as much as you can feel the result. Especially if you jump off the throtte in the middle of a hard turn and go spinning

davidfarmer

I think that is pretty common in first and second gears, where the engine has a significant torque advantage over the wheel speed. That is why the new Z06's have an engine-brake warning that comes on if you download, and actually adds throttle to the engine to prevent this.

As above, your wheels didn't "lock up", they just moved slipped....I'm sure that's what you mean anyway.

This is specifically why we rev-match and heel/toe during downshifts. It's usually not a problem during same-gear deceleration, as you hardly ever have a braking zone following a 2nd gear straightaway.....as a matter of fact, I've never been on a 2nd gear straightway......

OzzyTom

thanks for responses....
I understand about rev matching on down shifts..... but I noticed a momentary "chirp" from the rear tyres when I lifted off the throttle after a flat run in 2nd gear to near redline..... no down shift, just lifted off throttle to coast down during some shake down accelleration runs.

Like I said, I hadn't experienced it from engine braking alone with any other vehicle, and was curious if it was typical behaviour.
Rafteracer considers it typical, so I'll keep an ear out for it if it occurs again.....

thanks

Mike P

OzzyTom,

Yes, that is completely normal for a high compression motor. I have the same thing happening in my '68. It's an autocross car with a triple disc clutch and a flexplate (ie - 15 lb rotating mass at 6"-7" diameter VS. 40-50 lb rotating mass at 12"-13" diameter stock). I get pretty annoying corner entry oversteet due to the rear wheels slowing down faster than the car and sliding, causing the oversteer on entry. They're not locking up, or I don't think they are, but just slowing too fast.

I'm changing to a JW "Wheel" flexplate in the next few weeks to add some rotating mass to the clutch. Should just about double what I've got now. Still nowhere near the stock level, though.

Mike P

Lancer033

is that the same thing they've been talking about not having in Formula 1 this year?

Jim_Harrison

Mike;
Nice to see you are still around, missed you at Nats, the last few years. I resolved my rear lockup off throttle by;

Reducing the amount of rebound in my shocks, (I have dual adjustables but a shock that is too firm like the the Bilstein extremes will cause this.

Heavier front springs, I would suggest 550lb for the street.

I have stock pads in the rear semi metalics up front.

Dial in a little rear toe in...I have a bunch.

Ozzy Tom if the car isn't getting loose on corner entrance, only chirping the tires, I wouldn't be concerned but if it is wanting to come around then time to do some suspension mods.

OzzyTom

Thanks for that further feedback. I have got a lightened flywheel which I guess may be contributing a little...

Jim, It's not bringing the rear around.... well not on a dry surface anyway. Like I said, I was just surprised that it did it under simple throttle lift off.
Your suggestions of beefing up the front suspension makes perfect sense if it does become an issue.... reduces front dive and subsequent unloading of weight at rear

Thanks to all...

ZR1 MK

Im guessing you have an aggressive clutch and small low traction tires.