Saw ring and piston swap, then saw 13b asked myself that's not right? Then retread your post susiemk and all became clear, what do you have the rotor in.
Just saw this sorry for the late reply
I was talking about a ring & pinion swap in the rear differential for a different final drive ratio.
My bud is an old school import drag-racer from Puerto Rico & has 2 KP61 Toyota Starlets with Rotary swaps.
"Fast" car is a simple old school back half'd ladder bar car with a G-Force 2000 sequential dogbox transmission, spec triple disc minilite clutch, PP 13b homemade from a $100 donor 6-port 13b, ford 9" rear, smallish 12" tires - again best 1/4 mile time 8.41 @ 161.50MPH...
"Slow" car has everything above except is on a 70's toyota celica 5 speed transmission, has a cheap clutchnet PP & custom single disc, has a chevy 12bolt rear, & small 10" wide tires - its best 13b 1/4 mile time is 9.78 @ 141+ MPH (ran 9.97 @ 133MPH on a pp12a)
Everything is fab'd, built, or tuned by myself and/or my buddy - he is an excellent welder with a gift for porting/polishing / fabricating, while I have alot of patience when it comes to getting all clearances perfect on rebuilds / new builds & can tune the cars w/o too much drama.
I also spec the cars out in terms of combinations of turbo, I/C , exhaust, CR, fuel, ecu, etc + I have fun eeking out that last bit of performance out of these cars by learning more on suspension tuning, wheelie bar heights, tire pressures etc...
Trying to talk him into E85 (available near one of the dragstrips we use) but he is stuck on VP race fuel @ the moment.