Hey guys,I have an 88 with an Lt1/T56 and 4.56 gears.I was thinking of changing my gears to 4.10 or 3.90. I had a 94 formula Lt1/T56 and it had 3.42's and I changed them to 4.10's.I loved the 4.10's and I also like the 4.56's
but I was just thinking of changing the gears.

 

I run 3.89 in my Formula with a 9"/T56.

 

I’m in the process of gathering the parts to do a T56 swap in my L98 IROC..are you happy with the overall performance of the 3.89 gears? Many here suggested 4.10, but I’d prefer just a bit more fuel mileage if it doesn’t hurt the overall performance severely going with a 3.77-3.89 gear.

 

I think they are perfectly fine. I am going to install a procharger, so I based the gears off gas mileage and 4th gen RPM assuming a trap speed.

My Ls1/T56 Iroc has 4.10 gears and they are pretty nice as well! I don't think you will be disappointed with either. I was sway to 3.89 if gas mileage is of any concern.

 

This is exactly what I needed to know..thanks!

 

with the 6 speed and 3.90's im doing 70-80 at 1800 so you could go higher and still have great gas mileage lol

 

I'll give 2 points of advice on this.

1-Be sure you know which T56 you have. Some have different ratios, and you may want more or less gear. Be aware of it for comparisons
2-Go find a gear ratio calculator online.

 

Both are good suggestions. My T56 came from a ‘94-‘95 F-body, and has the taller 2.66 first gear, which is completely unacceptable with the 2.77 rear currently in the car.

 

My 94 formula had 3.42's and it was just to high,I went with a 4.10 set out of a 94 S10 and it was a great gear and the gas mileage was about the same.

My 88 has 4.56 gears and I love the way it drives and it still only turns 2100 rpm's at 70mph.

I dont think i would put 3.73's behind a t56,I think it would be to close to the 3.42's that came factory behind the T56's. That is why I wanted to hear from guys running 3.90's.I do think the 3.90's would be a good gear.

 

You've already had 4.10 gear so you know what that is like. 3.90 ratio is only 5% less so you probably won't even know the difference.

If you're going to select a gear ratio then you really need to consider torque applied by the tire to ground. I have 3.73 gears and it works well but my engine makes a lot of torque. If I put 4.56 gears in my car then it would become a spin fest because I could not harness the torque to ground.