Rear diff ratio decision

[supra90mkiii]

Hello all,

It's been a long time since I've posted here.

I recently noticed that Driftmotion.com sells rebuild/upgrade ring and pinion kits for our mk3 supras. A few years ago I was trying to find a replacement ring and pinion with no luck. Since DM.com now has these in many different ratios, I need help deciding which is best for my setup.

I currently have a 3.90:1.

My car is a 90 Turbo 5-speed r154. I run 275/40R17 Toyo Proxes TQ tires in the rear, and on race gas I put down 513hp/455tq.
It's been years since I went to the track, but last time I remember, I was at the very very top of 4th gear when I crossed the finish (I had a terrible launch, 2.5' 60-foot, trapped a 121mph.)

So I need to decide between 3.90:1 or 3.73:1.

3.90:1- spins in 2nd a bit. At red line at the end of 1/4" mile race.

3.73:1- Possibly better initial grip/traction. Higher top end speed. Slightly slower acceleration.


Any tips?

 

[Piratetip]

If you aren't looking for epic 0-60 times you could go with a taller 3.73 ratio.
But don't expect it to help you off the line much.

You can also switch to an even taller 3.58, I have performed that upgrade for a couple people already.
I have another diff coming to me soon for that same upgrade as well.
That custom R&P can be sourced still, until the supply runs out.

Latest diff I have upgraded:
http://www.supramania.com/forums/showthread.php?245610-Another-Custom-3-58-R-amp-P-LSD-Rebuild

Check the calculator in my signature, there is a gear ratio calculator there.
I am working on updating it with some more information soon.

Some of the issues with the gearing come from the R154, the gear ratio spacing isn't ideal for racing applications.
Some gears are too short/too tall & the spacing between them is not the best.

If you cant hook up power to the wheels, look at the tire selection/temperature/pressure first.
Though I am surprised you are still spinning a Drag Radial at that power level.

 

[supra90mkiii]

If you aren't looking for epic 0-60 times you could go with a taller 3.73 ratio.
But don't expect it to help you off the line much.

You can also switch to an even taller 3.58, I have performed that upgrade for a couple people already.
I have another diff coming to me soon for that same upgrade as well.
That custom R&P can be sourced still, until the supply runs out.

Latest diff I have upgraded:
http://www.supramania.com/forums/showthread.php?245610-Another-Custom-3-58-R-amp-P-LSD-Rebuild

Check the calculator in my signature, there is a gear ratio calculator there.
I am working on updating it with some more information soon.

Some of the issues with the gearing come from the R154, the gear ratio spacing isn't ideal for racing applications.
Some gears are too short/too tall & the spacing between them is not the best.

If you cant hook up power to the wheels, look at the tire selection/temperature/pressure first.
Though I am surprised you are still spinning a Drag Radial at that power level.

Thank you for your quick and thorough response.

I don't spin in 2nd at the track, it's sticky enough there. I should have clarified that, only spins in 2nd on the road.