gear ratio questions

[thumper877]

I have a 69 camaro that is ready for the center section. It has detroit speed subframe, art Morrison 9 inch rear end with 35 spline axles I'm running a t56 6 speed trans. My motor is a stock ls7 but I may do a cam swap later and stay around 600 hp but for now it's the factory 505 hp. What I'm wanting is a car that will mostly be a fun street car be able to driven alot of miles. I want good highway manors but will also do a autocross here and there. I also want to do the powertour. Dont get me wrong i drive it hard.If anyone has a similar setup who can give me some advice I would appreciate it. The factory zo6 corvette has 3.42 and I love how they drive. Thanks for any help

[nokones]

For autocrossing, the 3.42 gear set is a good number to start with. It all depends on the course designs. You want to keep your shifting, especially downshifting to 1st gear, to a bare minimum.

[LS7 Z/28]

You didn't provide any information that is relevant to finding the right ratio. What diameter tires are you running, and which Tremec do you have? Here is a calculator which will let you figure out where you will be at MPH wise in each gear. The LS7 should be comfortable pulling to 7,000 RPM.

http://www.tremec.com/calculadora.php

The vette had a 3.42 in order to allow the car to reach the top speed they were looking for and be a good compromise for the roadcourse. The Z/28 has 3.90's which would be better for track performance depending on your trans ratios and tire diameter. Look at the calculator and see where you will be at with your trans and your tire size. It all depends on what you're looking for and different people have different preferences and opinions.

[thumper877]

Yeah that would probably help sorry it's a T56 magnum close ratio my tire size is 335/30/18 rear

[Z06vet]

If you cam it, I say at least 3.73, preferable 3.89. Personally I really like 3.89 or 4.11. Keeps motor in powerband- in that sweet spot. I have 4.10s with F body T56 and 335/30/18 tires. At 80 mph it turns 2100rpm. Not sure what ratio your trans has, but Z06 has more aggressive ratio in all but 4th gear (at least in the C5 Z06). Thanks for the link to that calculator- handy reference.

[LS7 Z/28]

I think you would be the most pleased with the 3.73's

You will be able to hit 50.5 MPH in 1st Gear at 6,500 RPM if you ever want to try autocross

In 6th gear on the freeway you'll be running 2000 RPM at 65 MPH.

I agree with Z06vet also that more gear would be optimal and more fun, but the 3.73's would be the best compromise.

One thing people seem to not think of is having a 2nd or 3rd gear set. 9" gear sets are easy to change out.

[thumper877]

Thanks guys I appreciate all the advice.

[nokones]

What ever gear ratio you pick make sure that you have great torque management for the best autocross times. If you have a lot of torque at the low end (450-475 or more at the wheels) and a tranny with a low second gear ratio (numerically 1.80+) and the rear diff with a low gear set ratio (numerically 3.42/3.45+) you will find that the torque management will be more difficult to manage and master on corner exit. The lower gear ratios usually will work OK on tight goat trail type courses but, normal flowing Corvette type courses you may have a problem managing the torque.

This is where a 9" or Winters Quick Change would come in handy when trying different gear sets between runs.

[TheJDMan]

I'm running a SBC, T56 close ratio, 335/30R18 and a 9" with 3.89. The combo is fun around town and can still cruise on the hiway all day long at 70.