gear ratios for a chevy

[hunter1991]

i have a 92 chevy and i am gonna sitch it to a sfa in the spring. i would like to run at least 35s and maybe 37s. its a 350 with few mods on it, nothin fancy, an automatic trans(i beleive its a 700r4). still not sure what ratio it has in it now but im lookin for suggestions. its a dd and im lookin for some fuel economy overall i guess. i want it to be good all around even if i have to tow some trucks. ive thought bout 4:10s cuz theyre pretty common... any ideas?

[GerryK61]

I have a 91 GMC 5 spd 4x4 with 38's(37.6inches) & I run 4.88 gears. Which work well for me I can run on the Hwy@ 65mph@about 2500Rpm in 5th. When I had the stock 265/16(31 inches)on it ran 65mph@2000Rpm and got 26mpg. Now its down to about 21mpg Hwy. If you do more Hwy driving I would stick with 4.56 gears. And with a 700R trans the 1st gear is pretty steep so plenty of power for crawling up Rocks ect. 4.30 would work well with 35's.

[hunter1991]

yea it seems to me that i mostly do alot of highway driving, or at least on back roads n stuff. is there any place that has gears for sale that isnt like 600 bucks a set?

[GerryK61]

I purchased mine through Summit Racing. If I remember correct the gear kits were about $150 each and the install kits were around $80 each. I also purchased steel braided brake lines for $100. The lines made such a big difference with 38's.
Good Luck!
Oh 1 more thing! I don't know if this applies to the 92 GMC but some 91 K1500 4X4's came with 8.2 front diffs. Make sure you check before you place a order.

[hunter1991]

alright ill check into em! thanks! ill be switchin to a d44 for the front end so i think i wont have to worry bout that problem. but i didnt even realize that they were different now i guess i just need to put it all on and then decide the ratios for the tires size that looks good... alotta work still

[GerryK61]

Check out this link. It will help you with tire size versus Gear & Rpm.
4Lo.com :: Gear Ratio & Tire Size Chart
I found it on this site.

[hunter1991]

the site helped!!!!! i tok my truck for a spin it runs 2k at 55 and like 2400ish at 65. that isnt showed on the charts and neither is the good ol 4.10 gears BUT i had looked at the calculators and that made a bigger headache... it couldnt tell me my ratio cuz my tire size is 31 when it used to be 32s... and the calc had also said to use like 4.10 ratios too with the tires size change...i want to get it as close to factory as i can, and would 4.10s actually do that

[GerryK61]

The chart states that 32 inch tall tires with a 4.11(same as 4.10) gear would produce 2805Rpm@65mph with a 1to1 high gear ratio which would be 3rd gear in a 700R . Since you have a 4spd 700R trans your 4th gear is overdrive .86 and should drop Rpms down to about 2400Rpms which is what you stated your truck does already at 65mph.
So if you want to run 35 and keep it in the same Rpm 4.56 gears would run about 2845Rpm using 1 to1 high which would be 3rd gear in a 700R.
So with your .86 4th gear overdrive you would be about 2400Rpm.
If you want to go with 38 tall tires then 4.88 gears would keep you in the factory Rpm range.

[hunter1991]

thank you! that makes more sense! i was just reading it as the rpms that it would make in the gears cuz thats what i was more concerned about... cuz i know that chart is just a guideline to help and i wasnt sure if there were more options... an if i have 4.88s tho.. ill be runnin 2400 in 4th gear.. i ran 2400 in 3rd. that wouldnt be factory at all