Increasing Wheel RPM on a Gen 2 FC3S
 

Hi...so I have a bit of a unique quandary. My RX-7 is a bit of an odd piece of work, as I bought the chassis with a busted 13B. It's got the usual 5-speed manual and 4.1 diff setup for a high-rev, low torque engine.

The problem is that now I have quite the opposite sitting in it. A low-rev (3-4k redline with an absolute maximum of 5k), and an absolutely metric ton of torque. At zero RPM. So much, in fact, that with the 16" tires on it right now, 5th gear (at 0.697 x 4.1 gear ratio) will put it squarely at 82 kph (or 51 mph).

I'd like to increase that by a fair amount, as with my engine, in first gear, I'd be sitting on (3.475 x 4.1) 321*14.2475 = 4573 Nm or 3361ft-lb of torque. Way, waaaaay too much.

Ideally, I'd like to either drop the diff's internal 4.1 gear ratio to maybe 2 or even 1, or change the transmission gears from the stock:

1st - 3.475
2nd - 2.002
3rd - 1.366
4th - 1
5th - 0.697

To something more like this:

1st - 1.366
2nd - 1
3rd - 0.697
4th - 0.5
5th - 0.35

Is such a thing even possible? Or am I relegated to seeing if I can bump up the tire size to 18" just so I can get anything even approaching freeway speeds?

Thanks for your time!

You can do a Ford Explorer 8.8 rear end swap and put in a 2.26:1 rear end.