what is my gear ratio?

[lsrex212]

ok...i have searched but i cannot find what im looking for....my truck is a 1989 gmc 1500 2wd ex cab shortbed. 5.7

im trying to figure out the gear ratio of the rear end to no avail....i have the numbers off the tag in the glovebox but i have no way of decifering them...i was told that it was second row close to center-will start with a "g"....but thier graph does not show the same "g" codes that i have...

the only one i have in that area with a g is "gu4"...the only other g is "g4b" can anyone help me with this please?
any help on figuring out the other codes would be great also...

[Movieguymookum]

GU4 = 3.08 ratio

[lsrex212]

thank you very much movieguy...now part two...how do i go about calculating the correct gear ratio with my 32 inch tires?...i want it to be pretty close to what the stock configuration was..or if thats not possible i will switch over and have the speedo recalibrated...what seems to be the favored gear ratio in this case....the truck is a daily driver so i want to retain a decent cruise speed/rpm with the od tranny...but i also want to have some balls as well....sorry for the long post and lack of knowledge on my behalf...i dont know what info will be needed to answer that question...so if you need more info lmk and i will give you more details....thanks...

[tRustyK5]

I'd go with 4.10's. Cruise rpm at 70 mph would be 2100 rpm. lot's of low end grunt too.

Rene

[Movieguymookum]

I can tell you what I got and what I get with them. I have the 3:42 posi rear and am running 32x12.50 15's with an BF Goodrich AT tire. I cruise 60mph at about 1600 rpm. It will NOT spin a tire on pavement for crap unless it is wet. I recently had my tranny rebuilt and the tech actually asked what tires I run and said the 3:42 was about the highest ratio he would go with larger tires and actually told me the 3:73 gears would be less of a strain on the rear and tranny than what I had. This is all in a K1500 Z71 with 5.7L. With the speed limiter off and the rev limiter raised by a HyperTech Power Programmer III, I have had this truck clocked at 122 mph by local police while on the way to a fire response. That was at about 4600 rpm.

As for pulling power.....I have hooked to a 93 grand am at a house that was burning and drug it clear of the scene with the e-brake on and tranny in park. Yeah, I was in 4 low, but it never missed a beat and never loaded up.

All in all I like the 3:42 rear and can not really complain. I get 17 mpg average unless I am playing or riding the city scene.

Hope this helps.