Square body chevy truck gear ratio

[etedeschi72]

Ok, I've got an '85 K20 4x4. Its got a 454 engine, a SM465 4 speed transmission and what I believe (99% sure) are 4:10 gears front and rear with 33x12.50x16.5 tires. I really don't know anything about an RPM range or what a good one woul be but I'm just guessing around the 1800-2000 range. Now, my long term goal is to swap in an LS 5.3 and maybe an NV4500 but neither is happening any time soon. Anyway, I hate the low slow gearing that's in it now and want to change them. I don't use it for off roading or anything like that. It's my daily driver for Spring, Summer and Fall and I do tow trailers occasionally. So my question I guess is, what would be the best all around gearing for what I'm using it for? I'm looking for faster speeds, something that'll go 70-75 maybe on the highway and for occasionally towing. I've heard that 3:55's would be good. Someone please help lol

 

[Grit dog]

I have the same gear ratio truck and it’ll do 70-75 all day long….
You mean those speeds at lower rpm’s?
I’d suggest just spending 10 minutes with any of the online rpm/gear ratio calculators since it’s your truck and your decision and you didn’t provide some of the info needed for anyone to make a recommendation anyways. (Tire size and desired rpm’s at your desired speed). Plus you’ll learn quickly how to answer your own question.

 

[etedeschi72]

Thank you, I'll try it. I didn't realize until you said something that I forgot to put a tire size and RPM'S. I'll edit my post.