What diff ratio are you high hp boys using?

[winstontj]

Depends on setup... but

I disagree with you on that, turbos work better under load, a lower final drive allows you to build bost sooner in the rev range for a given gear.

My car would be horrible with a 4.10, it would rev out way to quick between gears, I'm using a 3.64 and it falls straight back into the power band when I change at redline.

I suppose everything is up for debate since the only identical motors out there are the stock ones from the factory and all of your turbo'd m20's are totally custom with different power curves.

The goal in mind when choosing gearsets for a turbo (or any car) is to keep the motor in the thick of the power band through every gear... and to get there quickly out of the gate. BMW chose the HIGHEST (low number = high geared) ever (at that time) rear end gear for the 2002 Turbo, a 3.36LSD gearset. They also mated the motor to a CR gearbox with a lower first gear, closer ratio gears, hence the CR box, and a 1:1 final drive (5th gear) ratio.

Rather than ask what everyone else is doing do some math, calculate top speed and RPM and choose from there.

Turbos like CR boxes in general and low numbered (high geared) rear ends. That being said I suggested a ~3.73 ratio assuming that you guys will be using OD gearboxes. The gaps (rpm differences between shifts) will be brutal, you will have to shift more, but you will have more choices when pulling out of a corner, coming into a corner, etc.

Talk to VAC motorsports and get a custom gearbox made up that wont blow up with any gearset you want.... then you can build a gearbox around your motor and your diff...