Anyone wanna trade their 3.9 for my 4.56 final drive?
 

I'm really looking for a 3.73 final drive for my LS swap but I'm having some trouble finding one. My 2nd choice would be the 3.9 from an auto 86. Would anyone be interested in trading their 3.9 for my 4.56 from Weir performance?

ATs come w/ 4.1 stock

you can see if you can find an is300 M85 manual diff, those can swap in for our cars and come with a 3.73 gear if you are lucky enough to find a used M85. They have been known to handle around 700 WHP reliably.

I have a OEM Auto whole pumpkin ready to be shipped if you want to swap.

Does the auto come with a 3.9? Or just the same 4.1 with a different gear ratio?

The latter. ATs have 2 overdrive gears and 4.1 FD. 2017+ MTs have 4.3 FD and one overdrive gear.

What does that mean? I've never raced my car but when I played Forza, one of the things you could change was gear ratio, and I noticed that tweaking certain gears helped the top speed, but I don't know why.

Removed all info he doesn't need.

I watched Ebay at least 2 days a week for about a year. Finally found an M85 IS300 diff for 350 shipped and nabbed it. They are seriously sought after and hard to get, but be vigilant and your efforts will be rewarded. Maybe someone will trade though, best of luck!

Mr_Eyo: are you sure? I thought that 4th is direct drive on our MT gearboxes, with both 5th & 6th being overdrive.