Gears

[pony14]

I recently had the rear differential worked on replacing all bearings and the stock 3.27 for 3:55's on a 99 GT Vortech supercharged mustang. What should the difference really be other than that I need to change to second quicker and that the speed shows about 10m/h slower? I will add a speed cal. this week to take care of the m/h difference versus playing with the chip. I do feel the take off a little quicker but have not been out to a safe track to test completely.

[helga123]

Actually, I think you about hit the nail on the head.

A bit more acceleration, shifts come a bit quicker, and depending on the track, you might be slightly better/worse (what gear what corner type of thing) but not really a major change. Hell, weather would probably affect things more.

You know your car & post after you've had a chance to really compare, but I would be surprised if you came back & said "wow".

I went from 3.27's to 3.73's on my 5.0 vert and my conclusions were a) Just what I needed to make 1st gear more useless- thanks b) It gets to the point of not breathing quicker, so I really ought to add that 9 psi Powerdyne that's still sitting in the box- like your Vortec that would actually accomplish something [Shortshifting is better with the gears- waiting for revs is like watching grass grow] and c) 3.55's would have been a better highway choice- I'm making more noise & using more fuel but not a whole lot else on an otherwise stock car.

[Chucko]

I went from stock 3.08s to 3.55s and a close-ratio T5Z on my '89. The motor is a mildly modded N/A 302 that pulls hard to 5500 RPM. This is a great combination, but for highway use I think I could go down to a 3.27 and it would be perfect. A 3.73 might be best for the strip, but I never play at the strip. I need to get it back out to the road courses.

With a centrifugal blower or a wild N/A motor, you're making a lot more top end HP, so you can get away with steeper gears. Mild N/A, strokers, nitrous, or positive displacement blower setups (Kenne-Bell) make a lot of midrange torque, and so don't need quite so much gear.