Rear gear ratio question

[caesarmascetti]

Hi guys is there any way to know what the rear gear ratio is? I'm running a T5, with a 347 stroker, at 70mph Im turning 2,000rpm

[Gordon Levy]

I am assuming you are in 5th at the time. I would say ether a 3:27 or 3:31

[caesarmascetti]

I am assuming you are in 5th at the time. I would say ether a 3:27 or 3:31


yes thanks very much

[steno]

I’d say Gordon is right on... with a 308 year you’d be going about 77-78 mph at 2k

[Jeff Kleiner]

Since there may be some speedometer error try this---jack the rear of the car up, mark the tire and the driveshaft and count how many revolutions the driveshaft makes for one revolution of the tire. 2 3/4 turns=2.73, a little more than 3=3.08, 3 1/4turns=3.27 or 3.31, a touch more than 3 1/2 turns=3.55 and about 3 3/4 turns= 3.73.

Jeff

[caesarmascetti]

Since there may be some speedometer error try this---jack the rear of the car up, mark the tire and the driveshaft and count how many revolutions the driveshaft makes for one revolution of the tire. 2 3/4 turns=2.73, a little more than 3=3.08, 3 1/4turns=3.27 or 3.31, a touch more than 3 1/2 turns=3.55 and about 3 3/4 turns= 3.73.

Jeff

Interesting you mention this, I checked the speedo when I first bought the car it is the GPS unit, versus a handheld gps that I had and it was spot on

[DadofThree]

For reference, as Gordon states, my stock 302,T-5 with 3.08 does turn 2,000rpm at 78mph.

[bobl]

Your GPS speed will be accurate. If you get the RPM in 4th gear (which is 1:1 ratio) at 70 mph you can plug those numbers into this calculator to figure your gear ratio.

http://www.wallaceracing.com/calc-gear-tire-rpm-mph.php

You'll also need to measure your tire diameter to assure accurate results.