The LT1 motor and T5 trans are in my '89 and I've started the wiring harness. The PCM was sent out today. Slight issue is that they need to know, which gears I will be running. Currently, I have the 2.73's. I'm going to swap in either 3.42's or 3.73's. Any opinions on which gears to go with? Also, the T5 is staying in for now (until it breaks or I find something stronger). Any advice is appreciated. Sorry if this is posted in the wrong section.

 

I'd recommend 3.42 gears since you are short a gear. The T-5 isn't going to hold up against an LT engine unless you are light on the throttle.

 

If the T5 was behind a TBI, then it has the 0.63:1 fifth. If it was behind a TPI, it has the 0.73:1 fifth.
With the 0.63, I'd run a 4.10:1 gear. That'd be best for low elapsed times, plus deeper axle ratios effectively reduce the stress on the transmission, whether stick or automatic.
LT1s still get good mpg even with way too much cruise rpm. I did 22 mpg running 80 mph at 2600 rpm, in my '95 Z28 convertible.

 

I'm not sure what the T5 was behind before I got it. You have some good knowledge of the gears. I really need to learn more about gears and ratios.

 

If you have the trans out of the car now, put it in 5th and accurately mark the top of the input shaft and the output shaft. Now turn the input exactly 1 full turn and see where the output is. Is it closer to being 180 degrees from where it started or is closer to 270 (3/4 of a turn) from where it started. If it is the .63 ratio, I would agree on the 4.10's. My T56 has a .63 ratio 6th gear and with the 28" tire I plan on running, my 75 mph cruise rpm will be 26xx with the 4.56 gear I'm going to swap to. A big OD gear is nice for this.

If you have the other ratio 5th gear, then the decision may come down to how much highway driving you do and what are you expectiations of the car. On a stock size tire, even 3.73's with the .73 overdrive will have higher rpms in 5th gear than 4.10's with a .63 overdrive at the same speed.

Here is a link to a calculator you can play with. Just put in the size tire your running, the axle ratio and your trans gear ratio.

http://www.fbody.com/calc.htm

 

 

Thanks guys.

 

Based on the trans tag (1352-176) it is from an '88 TBI w/ a 5th gear of 0.63:1.

 

Not entirely true. My T-5 lasted 2 years behind a Hotcammed LT1. Synchros didn't last more than a year, but everything else was fine. I hammered the crap out of it though.

 

With all due respect, I believe your experience is just more proof of what I was saying =)

 

That's why I said not entirely Stock LT1, T5 will hold up fine.

 

I will probably do some hammering on it. As long as it lasts until I find something stronger (i.e. T56 or TKO 500/600).

 

hehe, good luck =) With hammering your synchros will be lucky to last a month. Be easy on it, and you might get a year or so out of it. The T-5's from third gens just weren't designed to put up with much of a beating.

 

whats up guys. i havent been on for a while. hey TexasLT1 you pasky helped me out with my lt1 install and i have a t5 on my lt1 since 2004 and its still working good. when i drive it i get on it no problem. although i do have fan relay issues and charging issues its all good

 

Hehe, goes to show there is always variation in all things. I hope your T-5 Experience is just like his, lasting 6 years is great!