LT1 with a mild cam,
2400 stall,
3.73 gears,
Eaton posi,
4L60E tranny,
245/50/17 tires

I don't like 3.73 gears, the RPMs are too high on the highway and my MPG is not that good. So I want to switch to 3.23 gears.
I once had 3.23 gears with a stock L05 and rather liked it, it was snappy in town while still offering enough top end speed.

Also had 2.93 gears and didn't like them, too high a gear, terrible in the city even with LT1. They did however get OK MPG on the highway.

Realistically my choice is between 3.23 and 3.42. I estimate by going to 3.23, I should get + 2-3MPG. I looked at the gear calculators and by going from 3.73 to 3.23 my RPMs should lower by 300 at 70 and end up at 2,000, typical highway speed. Am I correct in assuming that this will mean better MPG? Problem is, I am not really sure of my cam specs and what RPMs it likes, the PO put it in but as far as I can tell, it's a mild cam. It idles just like a stock engine.

I do suspect that going taller than 3.23 will actually hurt my MPG, especially in the city as I might be working outside the power band of the engine/cam. 3.23 seems to fall right in the middle between 2.93 which I found too tall and 3.73 which I find too low.

3.73 is fast as h3ll in the city and up to about 50mph but lacks top end speed, is not the best for MPG and the engine is too noisy for my taste.

The question that I have is what speed should the torque converter lockup to get best MPG and not overheat the tranny? I think this is done via PCM? Also at what speed does the 4L60E shift into overdrive?

 

You will probably get a better response if you post this on LS1tech.com... here the majority yank their ECM's out and everything else that connects to it...

your 3.73 may not be your problem... you might be able to get a custom tune and fix your concerns of poor fuel consumption while street driving... you need to talk to someone who deals with LT1's and see if you can change your fuel tables at different throttle's...

 

for an lt1 go atleast 3.42, they work the same as 3.73's but give you better mpg. lt1's don't have as much torque as our l98 cars so you need some gear too move it, I once had an 93 lt1 car and switched to 3.73 gears and hated it but yes it was fast as hell but liked my 3.23 better so 3.42 is the way to go....

 

I got the specs for the cam and the Torque Converter:

Competition Cams Comp cam LT-1 LT-4 Chevy 93-96

* Application 1993-1996 Chevy 350 LT-1 and LT-4 engines
* Power Range 1000-5000 RPM
* Idle Quality/special requirements-Best for original LT1 with stock computers
* Valve Lift 500/510
* Adv Duration 266/276
* Duration @.050 210/220
* Lobe Centerline 114


TC:

GM Big Shot 12LS
This converter is primarily used in Street Rods that are slightly modified and always street driven. The Big Shot 12LS is an excellent converter for long distance cruising with mild performance increases, good lockup, and minimal MPG loss. This slightly higher than stock converter produces good idling with mild street rod designed cam shafts. Rear ratios should be in the range of 3.23 to 3.73.
Stall speed range: 2000-2400 rpms.

 

trust me 3.42, not unless in the future you're planning on big mods

 

I don't plan on any heavy mods, just a daily driver.