My dumb question of the day (and I promise to try to keep it to just one).

What would be appropriate rear end gear ratios for a 350 with a TurboHydromatic 350?
We will probably pull the Powerglide and swap in a TH350 before it gets on the road. Right now the existing rear end is a 2.73.

Thanks.

The t350 has a much shorter first than the glide, so regardless you will have a lot more torque off the line. Both have a 1:1 high, so the axle ratio is a trade-off between speed and power. With a typical 26" tire, a 3.08 will rpm about 2400 at 70, a 4:11 about 3500, but the 4:11 will be much quicker off the line and accelerating thru the gears. 3:40-3:50 is a reasonable compromise on a street car that doesn't see a lot of highway time.

What you do with the rear gear will depend on your goals for the car, obviously, but here's what I found. I switched a bunch on things at once, so I can't judge what made the biggest difference.

When I bought my 68, it had a 327 that had been "rebuilt" at some point and the original Glide. 2.73 open 10-bolt. It couldn't turn a tire in a puddle of water.

I rebuilt the 327 with a Performer cam and intake, and used headers instead of manifolds. I put in a TH350 with a slightly higher stall converter (1800-2100 RPM), and left the original rear alone. Between adding a "real" first gear, just a little more stall, and the slightly stonger engine, I could turn that right rear until it was bald (or until I'd puke a piece out of the 161,000 mile 10-bolt...). With a rolling start, it would haze the tire until it caught second. Posi and wider tires would have easily hooked it up, I suspect.

My friend has a slightly wilder 350 with a TH350 in his 68 vert, and it is very happy with nothing more than a 3.08 in an 8.5-inch 10-bolt posi.

I guess what I'm trying to say is think out the whole combo, which is obviously what you're trying to do. It is pretty easy to be traction limited on these early F-bodies with street tires that fit reasonably well. You may want to wait until it's together and running before you decide, given that changing the gears is one of the few things that's almost as easy to do while it's in the car.

If that's the original 8.2-inch 10-bolt rear, I'm not sure what gears are available aftermarket. the lowest Richmond listing I see is 3.36, which would probably be a nice gear. Randy's Ring and Pinion does list a Yukon 3.08 gearset for the 8.2.

Sorry to ramble, but I have known more than a few people who went big on gearing without thinking things through, and regretted it later.

I had a 350th and 2.73 posi behind a 406 sbc and anything below 40 on my speedo was smoke when I hit WOT. Best the car ran with that set up was 13.5@101.7 with traction (only used two gears). It would cruise 80mph at 2300 or so. Also having fun with the "ricers" running 1st to 80mph at 6000rpm and hit second would suprize them (most muscle cars aren't known for top end speed).

Anyway, go ahead and see how you like the 350th with the gears you have and you can always change later.

Thanks for your thoughts guys!

This will be a 99% daily driver. I'm just looking around for a good over all fun street ride for my son. I'm sure my boy and I will hit the "Midnight Madness" fun drags a few time just to see what it will do, but it's really just going to be a regular old transportation car.

Maybe I'll just concentrate on getting it going, and see what happens like you advise. It just seemed like 2.73 was awfully high..............

For 1968 entry level powerglide sport coupes, std gear ratio was 2.73, econ was 2.56, and perf was 3.55. With air conditioning, std gear ratio was 3.08. T-350s were option on higher performance 68 models. In 1969, entry level automatics used T-350s. I am switching from original powerglide with 2.73 to T-350 with 3.08 (and Eaton Posi). If I add a/c later, the gear would be like original. What engine do you have Supertrunk?