[GeorgeSmooth]

What kind of gains do you think our cars will have with shorter final drives?
I.E. the guys with manuals have moved to 3.46's from the auto's. Are the gains noticeable or very minor.
I have been toying for a while on installing a M3 diff with a 3.85 ratio. This will also give me a chance to compare the Quaife to the Motorsport diff. I am just wondering what the gains will be like on say over a quarter mile.

[Tortfeasor 335xi]

Swapping rear gears is old hat in the American muscle game. Swapping up to bigger gears can be worth a tenth or two in the 1/4 mile, or at least, I know when I swapped rear gears in my Mustang a decade ago, that was what it gained.

Actual acceleration depends on traction and power under the RPM curve used during acceleration minus the time you lose due to having to shift more often.

[Slidewayz]

I would think a numerically lower gear would be better for a tuned 6MT...you lose so much traction in 1st, 2nd, and 3rd with the 3.08.

[GeorgeSmooth]

Originally Posted by Slidewayz

I would think a numerically lower gear would be better for a tuned 6MT...you lose so much traction in 1st, 2nd, and 3rd with the 3.08.

So basically you are saying that the car actually needs longer gears. A bit of proof of this is the guys that manage to do good pulls starting in second gear.

[FastLane]

Swapping gears can really alter the overall dynamics of a vehicle and it can create unwanted noise and vibrations as well. For better or worse, it can alter fuel mileage and acceleration which are probably the most addressed attributes along with top end velocity. The one thing I wished BMW changed in the manual was a larger RPM drop from 5-6 gears. It's only roughly 300 rpm or so (at 80 mph). Though I am assuming BMW chose the best fuel mileage/6th gear accel for the gearing...I hope.

[GreenPlease]

^
Yep. The mechanical advantage endowed by shorter gears isn't worth a whole lot if you burn through first and second... car has to be able to use the extra torque at the wheels (e.g. bigger/better rubber) for it to make a difference. The AWD guys would probably benefit a lot from shorter gears. Just my $0.02.

[GeorgeSmooth]

Originally Posted by GreenPlease

^
Yep. The mechanical advantage endowed by shorter gears isn't worth a whole lot if you burn through first and second... car has to be able to use the extra torque at the wheels (e.g. bigger/better rubber) for it to make a difference. The AWD guys would probably benefit a lot from shorter gears. Just my $0.02.

First and second are only 4 seconds, I would be more interested in the gains on the rest of the gears. Assuming you changing the final drive you would be doing it whilst you doing a LSD installation.

[roozie2001]

im wondering the opposite. Im wondering what would happen if the auto went to a 3.08. 1) i think we would get amazing gas mileage. 2) i got torque for days in 1st and 2nd gear. I wonder if that would tame the car into even better 1/4 mile cars cuz i can give it more down low rather than having to feather it so much in first. If i over throttle in first i can kiss my start goodbye and have to play catchup