[danhr]

If you are dead set with sticking to your current transmission, then a general good rule of thumb is this

Fit the tallest tire you can under the rear of your car, width would depend on your hp level.

Choose the gear ratio that will put you roughly 200 rpms past your redline in 4th gear. That's the part that is kind of tricky as you have to roughly know what your trap speed is going to be.

So before deciding on what gear ratio you are thinking of going with, what size tire do you plan on running and what kind of transmission are you running?

Just to throw some numbers around, say if you have a transmission with your power gear being 1:1 (most are), and you have a redline of 6300 rpms. If you run a stock height tire, and run 4.10's, you will be limited to a 131 mph trap speed, or else you will be going into over drive (if you even have over drive). Same scenario, except with 3.73's will get you 144 mph at redline in your power gear.

Honestly, unless you plan on throwing some really tall tires under your car, I would either opt for 3.73's, or staying with the factory ratio. or you will just flat out run out of gear.