[bcacali24]

hi im 15 and i have a 1991 gmc suburban with 33 in tires
im rebuilding the motor right now and it should be around 300 hp when im done
im not sure what the rear end ratio is in it now but im sure its stock
before i started building the motor the burban had no power and bad gas mileage (around 10)
my question is would a switch to 3.73's help my around town power and gas mileage?
i wont be doing to much hiway driving but i dont want to be on the hiway running 3500 rpms or something.


So should i switch to 3.73's with my 33 in tires?

thanks for any imput

[GMCTRUCKS]

It might have those gears already check before doing anything.

[bcacali24]

what is the easiest way to check?

[400smb_s10]

Count the teeth on the pinion and crown gear and then divide the two and that will = the gear ratio.

[bcacali24]

thanks

i will check that but say i have lower gears than that what should i do
did any suburbans 87-91 come with 3.73??

[400smb_s10]

there is also another way but i cant remember the proper way it was make a mark on the yoke and diff housing then make a mark on the tire and spin the tire 360 degrees and count how many times the driveshaft turns to 1 revolution of the tire.. Cant remember the math you have to do but I think that if the driveshaft turns 4 times to 1 rev of the tire it equals out to 4:10 or 4:11 gears.

Hope this helps

Ed

[bcacali24]

it is a half ton 8.5 in 10 bolt rear

[400smb_s10]

Im not 100% sure I know I have a 1995 burban and it has 3:55 gears not 3:73's I also have a 1991 blazer that has 3:55 gears. It may have it may not have the only way to find out is to count the teeth. its an awfull stinky job but it helps to know the gears. I know i have a 1984 chevy fullsize with 2:56 gears *gags* Im swaping them out for 5:13 lockers

[willys36@aol.com]

Been discussed many times. A quick run of the search feature yielded this (one of MANY).

How to determine gear ratio in Ford 9"

[400smb_s10]

Ya 8.5 in but not a 10 bolt it was a 12 bolt that had the 4:11's its been awhile since Ive done one.... Im trying to knock the cobwebs out and remember how to do it!