Ok heres the story, I just bought an '87 GTA with a 350TPI, its got a TH350 and a 3.73 rear end...I love the power of the tranny but I can't take it on the highway because of the lack of the 4th gear overdrive....my questions are (a) can I adjust the selector arm and throttle pressure to make it better on the highway or should I put another tranny in??? (b) if i put another tranny in should I put the 700R4 or is there a better 4 speed w/OD auto i can put in??? (c) how much could I scrap a TH350 with 20k or so one it???

Thanks

~George the Greek

 

Put a taller rear tire on the car. Typical stock height tires are 26". It you put a tire closer to 28" it will be like going from 3.73 gears to 3.42 (rough guess). That will bring your highway rpms down. 275/60R15 is about right if you have room to make it fit.

Your TPI system doesn't like going above 5500 rpm anyway.

The 700R4/4L60 is a good street tranny but the low first gear is terrible for performance. The only other options for an A4 is a 200-4R and a 4L80E.
The 4L80E is a big heavy tranny. 80% of the internal parts are TH400 however a computer is required to operate the tranny.

 

Nothing to adjust that can help. th350 and 3.73's isn't a good combination for highway/interstate driving. Taller tires may help some, but won't have the same effect as an overdrive tranny. Taller tires will hurt off the line acceleration as well. Toss in a 700r4 and sell the th350. The 700r4 can be built just as strong as a th350. The 'too deep' first gear isn't a problem in a street car.