FruiTay

I am curious about a rebuilt differential with new gears. I don't know much about this subject and have tried to do some searching. I am following the "sticky" thread here in "autocross/road racing" and have bought many parts that were suggested. The diff is left out though.
I LOVE open track and HPDE but I also take looong drives so I wouldn't want an annoying rpm at 65mph, ya know what I mean? Thinkin' 3.90?

Thanks for the input guys! BTW my Z is an 01' with 45k miles on it and no signs of any leak.

Thanks again,

-Fruitay

Solofast

It depends somewhat on what track you are running frequently and if you are between gears on that track, but for the most part the 3.42 in the stock C5Z is a really good gear selection and unless there's some specific track where you need different gearing, there's no good reason to change it.

For autocross, going to a shorter gear set would be dumb, since you very seldom run out of second with the 3.42, and if you put in shorter gears you would be shifting to third a lot. And, since you can make the tail step out of line, even down low, in second if you aren't pointed straight getting more torque to the ground is the problem, not getting more torque.

Bottom line is that shorter gears are for drag cars, not road racing cars. It's been that way since the old Muncie "close ratio" four speed boxes, and nothing has changed.

geerookie

Most people find the problem is the transmission gearing not the diff.
Switch to the coupe tranny, it has much better spacing in the ratios. The Z06 tranny was geared to improve 0 - 60mph times but IMO it's terrible for the track.

RDnomorecobra

what they said. going to 3.90's would make it worse. unless you are drag racing.

FruiTay

I am no longer thinking about different gears. Maybe I'll have it rebuilt after I get some of these HPDEs starting in a month.

RX-Ben

Aren't we all drag racing down the straights?

Unless you are racing for prizes, the last place I would look for speed is the diff. My guess is that most diffs (clutch plates) are worn out and nobody can tell the difference. If you want to do anything get a rebuild and if you track the car a lot, take a close look at the trans output shaft for wear (missing tooth material). I was missing a substantial amount. If you have more power, go 30 spline and add a C6Z pinion support.
To give you an idea of how much difference a diff may make - I broke a friction plate in an OS Giken diff and lowered the TTA record at Mid-Ohio by a second, using the broken diff. Obviously this is anecdotal and "real" race teams go bananas with adjustable diffs, but 99%s are not going to be able to notice much.

fatbillybob

Thanks Ben! I need more reasons to NOT spend money on my racecar. But while I hear you loud and clear all the guys I race with are on OS or quaife and swear they are worth 1 second on our 2-3 mile socal tracks.