I have a 08 gt with a 5spd and when I'm going down the freeway at 2k rpm I'm around 70-73 mph. Is this normal with the 3.31's? Also on stock 17in wheels.I'm only curious because I'm thinking of switching to 3.73's and I'm wondering how much this will impact freeway driving. Also the previous owner I suspect modded this car pretty well before the dealer turned it back to stock. The sticker on the diff cover still says 3.31 but just looking for confirmation before I spend the duckets. Thanks for any replies.

 

Jack the rear axle up. Mark the ds and wheel and count the rotations.
Generaly easiest way to truely find out.
We also have a rpm calculator somewhere that shows speeds/rpms for differen gears/tire combo

 

Yeah I figure ill do alittle searching for a calculator. Worst case ill do some dirty work and figure it out for myself. Just trying to talk myself out of gears. I've already failed at talking myself out of a cai/tuner/short throw shifter in the last two weeks.

 

http://www.americanmuscle.com/ford-355-0510gt.html

Almost sounds like 3.55's, check out the chart they've got if you scroll down a bit. Also, I've got a spreadsheet that you input certain things and gives you an output that fellow member Nuke was so kind as to email me. I could possibly try to dig it up if you'd like, though the charts on AM help too.

 

Thanks . that's exactly what I was gonna look for. Looks like I'm gonna be buying some gears now.....