Alright. I have an 87 IROC 350 TPI with the common bolt ons. And I want to do a rear gear swap. I have heard that the stockish TPI motors don't like anything above a 3:42, do to you not staying in the power band as long. And the T56's don't like anything lower then a 3:73, do to it having such a low first gear. So this is my delima. The car is not a daily driver. So I can somewhat careless about the gas mileage. It dose do highway allot though. The car is mainly a street car. It will set both the dragstrip and autocross track a few times. So what gears do I need to go with. Thanks in advance for all the help! Adam :-)

 

I don't know why you think anything below 3.73s is not good for a T56---all the 4th gens had 3.42s.

Don't just look at the rear end ratio---its combo of the first gear AND the rear end.

Since the T56 has a lower numericaly first gear VS a 700R4---I don't see why 3.73s would be a problem.

 

3.73's will be perfict for you, I find 4.10 was little much for my TPI car plus with the 3.73's and t-56 the highway drive fit's into a more comfortable RPM.

 

Also don't forget engine torque, redline/rev limiter, and acceptable cruising RPM as well.