Hello All. I know my car for this discussion isn't a J-body, but I'm hoping to find some knowledgeable gearheads here.

I'm still searching for the deepest gearing possible for the 4t60-e trans in my 95 Pontiac Grand Am. I've got all the parts lined up for a 3.73:1 conversion, but I want to gear it deeper yet.

Follow this link to the GM Tuner Source and check out the differential kit offered for the 4t65-e transmission....

http://www.gm.com/company/gmtunersource/downloads/gmtunerhydra-matic_4T65_race_transmission.pdf#search='gm%20sport%20compact%204t65'

This a 4.00:1 ratio FDR unit....think of the gearing possibilities . With the 28/32 (drive/driven) sprockets offered you would reach a stump-pulling 4.57:1 ratio . NOT FOR DAILY DRIVING. I know it wouldn't be streetable....not interested in street driving with this car (stockcar).

Even if you wanted to try and use that combo for daily driving, find a way to keep OD and you still have a FDR in OD (4.57 X 0.705) equal to 3.22:1...that's still streetable. My non-overdrive Camaro was running 3.42 gears and I still got 17 mpg highway with a cammed-up 350.

Changing the differential on a 4t60-e trans is easy...remove an axle, mount bracket, a few bolts and a C-clip and the diff slides out...less than 2 hours on the jackstands and this job would be done. It's a little harder to change drive/driven sprockets but I'd like to see what kind of improvement it would make just by swapping the differential.

First off, I'm not worried about what the OBD 1 system in my car will read.....I don't care about that....there are ways around that I'm sure. I don't care about shift solenoids and codes at this point.

Will a 4t65-e differential interchange with a 4t60-e transmission. I know they use alot of common parts....is the differential one of those common parts?

If the differentials will swap, it would make for one hell of a surprise at the strip or a stop-light to stop-light race.

Any transmission guys out there have any thoughts about this.

Thanks for reading.