Black_Mamba

Been doing some road racing . I am hooked . Maybe a lower geared rear end will help me stay on powerband better according to my tuner and some friends. I am thinking 3.9, what would you guys recommend? Is the 3.42 working well for the guys racing on the OEM C6Z tranny?

Ed

Bill Dearborn

Works fine for me. I rarely use anything but 3rd and 4th. I doubt a 3.9 will really help and may even make things worse. The nice thing about the stock setup is you don't have to shift much whereas with shorter gears you will need to shift more and may not like the places where you have to shift. Plus, shifting takes some amount of time which means the car isn't under power for that time. In the long run it may be a wash.

Bill

mcar00

I researched this awhile back but related to the ACR. I found a couple of experienced racers who did exactly that and although the car felt faster their lap times increased. They attributed it to additional shifts and a lack of traction when powering out of turns. I know another accomplished racer who tried the change in a modified C5 Z06 race car and also went slower. I think the transmission gear ratio's can use some tweaking more so than the rear ratio. A better solution would probably be the ZR1 tranny.

Black_Mamba

Thanks. For what it's worth, I find the car well geared for RR given the engine powerband, torque, and weight of the car. I use second gear a lot on the two slower and maybe more technical tracks around here.

I am by far the less experienced driver on my group and not doing bad at all. Maybe not having to shift as much is an important factor especially against the (much) lower geared, quicker shifting GTRs.

Having a taller rear diff ratio will make me accelerate faster, right?

Ed

davidfarmer

it's all about torque at the rear wheels. Using 2nd gear will often overpower the tires, even in a stock C6Z, so 3rd and 4th are the primary gears. I use 5th occasionally, but not often. If available, a numerically lower diff might actually be more useful, giving you less torque (but more speed) in 2nd, and reducing how often you shift into 5th.

You don't want to get into a situation where you have to make extra shifts each last, as the time required to shift will likely take more time than the small amount of "useful" torque you'll gain.

Painrace

I agree with David. In a road race car with a quick change rear end and a dog ring transmission you set the rear gear just below the highest RPM max ypour car can achieve at the particular track. You would like to shift the minimum amount per lap with the maximum amount of torque so you then set the transmission to shift the least amount of to have the torque where you need it. Shifting kills lap time. I don't find 5 gear very useful so that would usually be 4th gear on a Z06. I think the 3.42 with a stock Z06 transmission is a good compromise.

Just my 2 cents.

Jim

quickc6

Nobody Makes gear for C6 Z06 . You would have to go to to the base
C6 rear end or convert yours it .Like others have said you don't need them.

bosco022

We found with our LS1 powered GTA cars that we could pick up nearly two seconds a lap at Daytona and a second a lap at Sebring going down to first gear in the slowest corners. These are Jerico tranny's with first geared like most 2nd gear (1.90). If your car will hook it may be a benefit. Of course the Jerico's offer clutchless/nearly flat upshifts.
much quicker shifting than a stock corvette box.

CorvetteZ51Racer

Just a technical clarification - taller rear ratio means numerically lower. That will reduce the amount of torque at the rear wheels and slow acceleration, but will reduce the number of shifts. Remember is this way - shorter gears mean the MPH range between gears is shorter. Taller hears mean the MPH range between gears is longer (you'll sometimes hear people call a tall rear end a "long gear").

Race cars that run the gear clusters to run about 2-300 rpm shy of redline in top gear at a particular track are usually doing it because 1) they can change ALL of the gears, not just the diff, and 2) the drivers shift fast enough that the increased time off the throttle is offset by the fact that the closer spacing of the gears keeps the motor in the power band a lot better. That being said, if you're not going to a full race transmission where you can set EVERY gear, don't bother. In my stock C6Z, I can out-accelerate almost any car I find on the track from 3000 RPM in 3rd gear exiting a turn than I can downshifting to second, because in second I'm modulating the throttle so much to avoid wheelspin (and that's on Hoosier A6s), that I haven't added any real thrust.

The other thing to remember when you're talking gear ratios in a particular case is that the shorter (numerically higher) gears actually have a LOWER torque capacity than taller gears. Because of the ratio of ring teeth to pinion teeth, the ring teeth get smaller (because there has to be more of them) when you go to a shorter rear end. In a heavily modified car, this could come in to play.

My $0.02

Black_Mamba

Much appreciated guys. Yes I should have posted "lower" rear ratio.

AU N EGL

When the very first C6 Z06 came out, or just prior too, one the test mules was at a NCM event at CMP.

That test mule had a 3.60 rear end instead of the 3.42. If I remember correctly even that 3.60 was too low

a 3.90 with that much HP will just spin the tires.

Black_Mamba

So how about with the C5Z where the power is much lower? I suppose the lower gearing on the trans makes up for it huh?

Somewhat surprised at some of the responses as I am not getting bad wheelspin on 2nd gear on my C6Z making 580rwhp. I was running Hoosier R6.

Again thanks a lot. I am just trying to make the best choices for my car and the responses from such a well respected community do help.

Ed

95jersey

There are more than a few guys who came from drag race set up and went road racing with 3:90's and they all said they were hitting redline fast and constantly running out of gear and shifting all the time. I think a few of the ECS guys tried this out and went back to stock if I am not mistaken.

AU N EGL

the standard 3.42 is still the ideal. a 3.73 could be a good choice for RR

3.90s and 4.10s one shift quite a bit.

95jersey

I would think 4:10's would force you into 5th gear on some tracks which in the C6Z 5th is a worthless overdrive gear. The car is really a 4 speed with 2 overdrive gears (one for country roads 5th and one for highway 6th).

96CollectorSport

Here is a gear calculator you can use to see what each ratio will do for your car.

http://www.f-body.org/gears/

Input your tire size, rear axle ratio and gear ratios for a C6Z it would be
2.66, 1.78, 1.30, 1.00, .74, .50

Then you will see what the differances are from gear to gear, if you have a good idea of what your max and min speeds are for all of the corners at the tracks you drive at you will figure out what works best for you. Remember to add a few mph to the top end so that you have room for improvement.

Enjoy

FNBADAZ06

What size rear wheel/tire are you running when your RR ?
You may find that, if available, switching to a slightly shorter tire may be a cost effective way to "shorten" your rear gear, in the same fashion as when you drag race.
Many change to an 18" rear wheel for this specific reason...more tire selections to meet their specific requirements.

I find that I spend most of my time in 3rd...4th on longer straightaways where I run in excess of 125+ MPH. The LS7 in stock form has such low end grunt, you can concentrate on driving the line without the concern of shifting.

Black_Mamba

Stock wheels with Hoosier R6 345/19

Autobahn93

I am putting a TR6060 Level 6 from RPM into me C6Z06 and went for "special" gearing .8 (5th) and .63 (6th).
Gear ratios of 1-4 remain the same.

Mid of this year I am contemplating of putting a 3.90 diff in which would give me a trans with 6 usable gears...
at least if I put the data into one of the online gear ratio calculators... I do not know whether it will be faster
for HPDE but I am sure it is going to be even more fun to drive on the street and track...plus I enjoy shifting

mcar00

I like that move! If I could change one gear in the C6 Z06 it would be 5th. Maybe even to like a .88. Let us know how it works at the track.