Hi all. Let me give you all a quick run over. Full weight 89 GTA with fresh 383. General specs are AFR 1040’s, 10.2:1 compression, 228/232 .545”/.545” 110 HR cam, Dyno Don headers, Speed Warrior dual plane, Sniper EFI. Have a M29 6 speed/heavy-ish SPEC flywheel (~28lb I think?)out of a ‘93 and finally a 9 bolt in the back end with stock 3.27 gearing and 275/40/17 25.6” tires. Btw, I May take to a track a few times but this is primarily a street/highway cruising car.

Now the question. What gear ratio would be optimal for this set up?
Options are 3.45 (prob not enough of a change), 3.7, 3.9, 4.11
The M29 gearing is:
2.97, 2.07, 1.43, 1.00, .80, .62

I have had 4.10’s previously with a 94+ T56 and 10 bolt. 1st seemed pretty steep sometimes until I put in a 306 cam then I appreciated it. However with the smaller cam In this 383 build would it be necessary, not to mention the M29 1st gear is even steeper than the 94+ T56

 

I'm definitely paying attention. I can't decide on what gear I want for my GTA.

I've got less displacement, and a larger cam, with slightly more compression.

But if it helps you at all. You can make a copy of this google sheet. i've got all the Transmission/Gear's programmed in, and you plug your tires in too. So it'll give you the RPM vs MPH in every gear along with drive-shaft speed in 5th and 6th gear too.

https://docs.google.com/spreadsheets...gid=1747947528

 

Awesome, thanks!

 

3.90 is the largest gear I'd put in a 10 bolt. The 4.10's snap like a pretzel. That at least puts a new upper boundary on your choices.

 

I don't know what your engine torque curve looks like but your trans ratios seem to favor the 3.90's over the 3.73, assuming you shift around 6000 rpm. Rips through 1st gear quicker, and finishes the 1/4 mile stronger in 4th gear too.

Either way, your trans gear ratios put in you a bad spot from a 55 mph rolling start. It's kind of nice to dust somebody from a roll if you want, but that might be a real weak spot for you after you change gears.