Gear ratios for rallycross?

[czei]

Hi--

I'm turning my '93 N/A Legacy into a dedicated rallycross racer, and am researching how to get more torque at low speeds. In rallycross you almost never go out of 2nd gear, so it doesn't really matter whether the car has any pull at highway speeds.

The car currently has an STi suspension and a newly installed 2.5RS engine, and the drivetrain is next on my list.

Is there a particular swap I could do to improve the low-speed torque?

Thanks!

[MConte05]

Getting the highest final drive will help you tremendously. 4.44.

[czei]

Sorry for the basic question, but is this a manual transmission swap from a later Subaru model, or an after-market part, or.... ?

[MConte05]

Usually have to search around for the right transmission. Search for Subaru Transmission Charts that has the ratios listed. JDM transmissions usually have very high Final Drives.

[Legacy777]

You can find some US based trans with 4.444 final drive ratios. The first gen legacies came with 4.111 & 3.90 final drive ratios in the AWD cars.

I'm assuming your 93 is a MT, but just want to verify.

Also, if you move to a 4.444 final drive ratio from the MT's 4.111, you may find yourself having to shift out of 2nd depending on your speed. Typically, how high up in rpms & speed do you get in 2nd gear?

[czei]

95% of the time in 2nd the rpms are under 4,000 RPM with top speeds in the 40mph range. The ground is so bumpy and soft around here you just can't go very fast.

One thing I don't understand is how just changing to a transmission with a different final drive ratio is going to change anything when those transmissions have overall lower gear ratios so that the overall gear speeds are similar. For example, my Legacy is a 4.11 and my Forester was a 4.44 and I couldn't tell any difference, i.e. the Forester behaved normally on the freeway in terms of RPM and power.

[Legacy777]

If the actual transmission gears are different, then yes it really won't matter as the final drive and transmission gear will both determine your speed. However, if the transmission gearing is the same, then yes just the trans final drive ratio should make a difference.