Hey y'all, ive wandered over here from the first gen section to hopefully have a question answerd. Im planning on doing the T-II swap into my 84, and am going to be doing some road racing. The thing is, is it possible the have the T-II tranny geared to so can run at 140+ mph at only 4K ish RPM's? I wanna run in the Silver State Classic next year. Help Please!!!!!

 

I would be thinking of rear end gears not tranny. Since you already have overdrive of about .7 or so.

I just ran my gear calculator and you would need about a 2.73:1 rear gear to have 140mph at 4K rpm

 

Is that possible to source from another car? Miata, etc... Trying to keep the costs down. Thanks!!!!

 

thats going to be custom, and your going to need a good bit of power to make that driveable.

 

Ive heard of gears in some old dinosaurs like Buicks, Pontiacs maybe Chevy's with huge CID engines running gears close to that. It would require swapping out the whole rear end but that would be way easier and cheaper than custom gears in the tranny.
I found some gears listed for the GM 7.5" 10 bolt on Summit Racing's site in the 2.73 to 3.08 range. Now just find which cars came with that rear end in a version close to the width you need. You might find one close enough that you could make up the difference with wheel offset or have it narrowed. If Richmond Gear is making ring and pinions for them they are probably very common. You might even find the gear your looking for in one car and install it in the 10 bolt housing from another car that is the width you want. Do some research and look through the salvage yards. I would figure you could get all the big parts for a couple hundred bucks. With a little welding you would be all set.

And snowball is right on the money, you will need huge amounts of power to run that gear. I would work backward from peak HP and what top speed you want. You may find that the rev happy rotary wants a gear above 3.5:1 even with a turbo. A rear end swap would open up a huge gear selection.