Transmission gears for track duty
 

My GR86 is a track duty only car. I spent most of my time on track in third and fourth. I don’t know the first thing about transmissions or gears, and don’t know where to start, but it feels like if third, fourth, and fifth were a little closer, I’d spend less time the lower rpm ranges.

I found some Cusco close ratio gears but they’re only first and second. I don’t think that would help me. Any assistance would be appreciated.

More than a few have changed the diff gearing to 4.56 or 4.88

Are you in 3rd and 4th in this specific track? Or all of the local area tracks you visit?

Every track is different. If you're spending most of your time in 3rd and 4th, it sounds like a track with lots of higher speed sections. And I think inherently with the power and weight of the platform, you'll find yourself in 3rd and 4th gear most of the time anyway. You'll pick up 2nd for slow speed/hairpins, and you'll only pick up 5th for long straights.

The car makes near peak torque with a flat curve starting at around 4500 RPM. If you're above that RPM, the car is in optimum range. Are you finding yourself in critical parts of the track where you can't make a downshift (and out of peak torque) or it's not ideal to upshift (and you're pegging redline)?

Motorsports teams have big budgets and will build and set-up a gearset for every track. Unless you only have one track near you and you love it to death, AND you're finding yourself out-of-power-band for critical parts of the track, leave your gear ratios alone.

I think different differential gearing vs trans gears is what I need. What’s the difference between 4.56 and 4.88?

4.88 gearing is shorter. You will find yourself in a higher gear or higher in the rpm band at the same speed vs 4.56.

.32 :lol:

You have to figure out where you want to be with your RPM's at certain areas of the track.

Are you having to shift right before a corner? Running out of gear, etc.

Are you bogging down when you want a higher RPM coming out of a corner?

There are gearing calculators all over the web and you need to find out how fast you're going at certain places on track and what RPM you are currently. From there you can move the gearing up or down. It's a bit of math.

Not the ratios you are asking about but a good reference chart.

https://www.jackstransmissions.com/b...ar-ratio-chart

Multiply current RPM *4.88 and divide 4.56 to get new rpm (or just multiply by 1.07). Not a huge change, but it's there. 6500 rpm becomes 7000rpm, give or take.

You'll also get a 7% mechanical advantage from the gearing. Kinda like having 7% more torque in each gear.