So I was fiddling with the ratio calculator on the Richmond site and according to the thing, at 60mph, 2800rpms in top gear with a 27.6 inch tire, I've got a 3.73 axle. (It says "Estimated 3.77 rear gear")

It also says, I'd have to be turning 2290rpm to have a 3.08 gear which is what I've always assumed I had, the car isn't quick off the line and doesn't spin tires so It can't be a 3.73.

So, when I buzzed the car up to 6200rpms, I was actually turning 6700? I don't know if I'm to be impressed or terrified.

I dunno about that, jack up the rear and do the rotation test.

If it is a 3.73 I'm going to have to rethink everything. lol.

I dunno about that, jack up the rear and do the rotation test.

Only way you'll know for sure :yes: And with an almost 100% stock 283, you could very well have 3.73's and not even know it lol

Jim,

I'm just thinking that my combo is way off on those calculators too, but I think its due to the converter slipping at cruise speed.

I'm running approx 3300rpm @ 60mph with 3.90 gears and 29" tires.

If you plug those numbers in you will see they don't match up.

Just something to consider.

That makes sense Greg, hadn't thought of that.

Come to think of it, I've seen one of those calcs that had a input for converter slippage %, can't remember where though. (Or how you'd guesstimate the percentage of slip.)