I've always been under the assumption that my 81 rear-end was at the anemic stock 2.87. That's the number I gave BTO when I ordered my transmission and the gears they put in for the speedo. But now I'm not so sure. (Tranny's not all the way in yet. We're waiting on the driveshaft at the moment)

I started playing with the RPM calculator on BTO's site and noticed that when I put in my tire size (p255/60 R15) and the 2.87 gear ratio, the 1:1 High Gear, (which should be correct for the stock TH350, right?) is WAY lower than what I get on the highway at about 70MPH.

Normall I run somewhere in the 3000-3100 RPM range at highway speed, but the calculation they came up with was 2,497 for 70MPH. That's quite a difference. In playing around with different ratios, I had to take it up to 3.55 to get closer to what I see going down the highway.

Now admittedly my tach could be off, I've never checked it against anything other than I know it's about right at idle. But this just seems really weird. And unfortunately, the car is a couple hundred miles away right now and I can't go spin the tires and count the rotations. I feel pretty stupid for not doing that before ordering the tranny now. Weird.

 

Get under the car and rotate the tire exactly one turn and count the driveshaft revolutions. If it turns slightly less than 3 turns in 1 tire revolution you have the 2.87. If it turns 3 1/2 turns you have a 3.55. Chances are your tach is a little off. This is a sure fire way to check the ratio, other than taking it apart and counting teeth.