I have 1982 302 engine with a 1969 c4 tranny. The rear is 8 inch 300 gears. The rpms at 50 mph is 2200. My question is what would be the difference in rpm's if I change the gears to 280's. The motor has small cam. I believe the # on the cam 303.
The transmission’s top gear is 1:1 ignoring slippage. Measure your tire height, then google for a rear end RPM calculator. The math should be pretty clear so that someone should have put it in a web page for us as a calculator.
The math just makes my head hurt today,
I have 1982 302 engine with a 1969 c4 tranny. The rear is 8 inch 300 gears. The rpms at 50 mph is 2200. My question is what would be the difference in rpm's if I change the gears to 280's.
He was looking for gear options to rev lower. My point was that with an AOD he could go up in gears and have more grunt at lower speeds (higher gear ratio) and still get lower RPMs while cruising. To get lower cruising RPMs with lower than a 2.80 will make the car a real dog out of the hole (unless he has a torque monster for an engine).
What is it you are wanting to accomplish? To get lower RPM at highway speeds? To save gas consumption? You should have my setup. A 3.89 rear end that is doing more like 3200 RPM at 60. Gas Mileage? Forget that question. I agree with the statement that what you would save in RPM is not going to justify the cost and hassel of swapping out the rear end. Bet you wouldn't even notice it. I am pondering swapping out my 4 speed for a 5 or 6 speed to get a highway gear. I hate to lose my Toploader though. I'd be looking for a newer AOD transmission. That makes more sense to me. A 2.80 rear gear? Most of us owners want a lower gear for acceleration.