foliva

It seems as most people have good things to say about 4.10 gears in the C6 on the street. Has anybody had any experience autocrossing a Z51 manual with 4.10 gears?

In my past experience with Solo II & my '93 6 spd, 2nd gear (stock rear) was perfect for Solo II. Since I just got the C6, I haven't been to the track yet, but just driving it around town seem to indicate that 2nd gear is about right for Solo II with a stock rear.

My concern is that if I upgrade to a 4.10, 2nd gear would be too steep
(class change issues aside). Can anyone confirm or deny this concern?

TedDBere

A C6 Z51 has the MN12 tranny with a 3.42 rear. That's a very good setup for SS and ASP classess. The reason it's not as good as the C5Z is the stock rims. You have 19s with no good tire. The C6Z now has several tires for it's rear.

But if you're changing your rear then you can also change your rims since you will be forced out of the stock classes anyway.

For autox you want a setup that will give you great low end accelleration and a second gear that will take you to between 65 and 75. C5zs get to about 70 and GT3s top out in second at around 82.

Use the available formulas and insert your chosen tire diameters, 2nd gear ratio, redline and either 3.90 or 4.10 and see which one can get you to about 68 mph. You may have to increase your redline to achieve those speeds with those rears.

Anybody have link to the formulas I'm talking about, I don't have the links on this computer.

Good luck.

dbratten

2nd gear is close to ideal the way it is -- as you are thinking. With the stock rear tire size (26.85" diameter) you can reach 73 mph in 2nd -- good for most SCCA courses. If you move to 315x35x18 tires R tires they will be almost the same height. You can even go to 315x35x17s and only lose 3 mph in 2nd dropping it to 70. I chose to go with the ZR1 17x11 rims all around for autox for now as a set of four is only $500 and tires are plentiful and affordable.

As you suspect 4.10s and even 3.90s are too steep with 61 mph and 64 mph max respectively even with the taller stock tires. If you run faster courses though, the 4.10s could let you run in 3rd with a top speed in gear in the mid to high 80s depending on your tire choice.

rhneff

Not only would changing the rearend force him out of Stock but also out of Street Prepared, so unless he's not concerned about being competitive or is ready to spend a lot of money to prep for SM2 he's best off staying with the stock gear regardless of any other factor .

foliva

Thanks for the input! Feb will be my first Solo II event with the new car ('07 Z51 manual). I'm interested to see how it'll do compared to my '93.

rhneff

I moved last year from a 96 LT4 coupe, after four years in the car, to an 02 Z06 and was surprised at how much different the Z was. Turn in was so much quicker I hit three cones in the first slalom I encountered, still being calibrated to the C4's response. Had to learn to drive all over again.

I expect the C6 will be similar. You'll be surprised how much more agile the car is. I still have my LT4 and really like the car, but the Z06 is just far and away superior and your 07 Z51 won't be far off that level.

Enjoy the ride, and keep the shiny side up .