figuring rear-end gear ratios

**67rivigs** · 02-01-2007, 04:07 PM

i am currently having a 455 built for my 67 riv. the builder needs to know rear-end gear ratio to select cam. okay, it takes 15.4 turns of the driveline flange to turn the drivers side wheel 10 turns fwd rotation. would that make the ratio 1.54:1? is there such a ratio? am i doing somthing wrong or has the gear-set been modified? I sure could use some expert advice.

thanks in advance
67rivigs

**bob k. mando** · 02-01-2007, 04:19 PM

if you have an LSD / Posi rear you can't do the "driveshaft rotations divided by tire rotations" trick without jacking up both rear wheels.

in your case, an open differential, you only jack up one side and the wheel goes half as far as your ratio because half of your rotary force from the driveshaft is spinning the differential. you have a 3.08, which is extremely common.

**67rivigs** · 02-01-2007, 06:36 PM

that makes sense since 1.54 X 2 = 3.08. will this rear-end be able to handle 500+hp/600+lbs torque? are there better options readily avaliable?

**bob k. mando** · 02-02-2007, 12:42 PM

i believe, but am not sure, that the 67 Riv is equipped with a 9 3/8" ring gear rear end. very large and very strong.

the downside is that there is NOTHING in the way of aftermarket parts for this gear set. also, the 1967-70 9 3/8" rear is completely different from the 1971-76 9 3/8" rear. you'll have to find full size GM cars/wagons from your era if you want to come up with 'new' ring and pinion sets or posi diffs.