Here is my Dilema. I own a '70 chevelle that came with a powerglide. I was thinking about swapping for a 350, but everyone has a different opinion on this. The car will be a daily driver but I still want to be able to be strong on the races. I have the option of beefing up my powerglide or installing a beefed up 350. One of my concerns is that when I drive on the highway with the powerglide as soon as I am hitting around 70-75 my rpm's are high. Can anyone help me on this and what would be the advantages/disadvantages of each situation? Thanks!! :confused:

I would go with the 350...

There's 2 things to note: Your highway rpms won't change by installing a TH350, and you could probably get better acceleration by having a steeper first gear than the powerglide has.

The final ratio for both powerglides and TH350's are 1:1. If you want to lower your highway rpm's, you either need to change the rear gear to a lower number, or install a different transmission that has overdrive, like a 200R4, or a 700R4.

If you want better acceleration than with the powerglide, I think any of the other automatics would help, because they all have steeper first gears.

Powerglide: 1st 1.76, 2nd 1.00
TH350: 1st 2.52, 2nd 1.52, 3rd 1.00
200R4: 1st 2.74, 2nd 1.57, 3rd 1.00, 4th 0.67
700R4: 1st 3.06, 2nd 1.62, 3rd 1.00, 4th 0.70

If you multiply the 4th gear ratio X you current highway rpms, you can see how much they will be lowered if you use that overdrive trans.

If money is an issue, I'd bet the TH350 is the cheapest, and easiest. The overdrives may take some extra work to install. Good luck!

chris