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Re: Axle Ratio? (archive)

[ Follow Ups ] [ 7-series (E32) Message Board ] [ Msg. Board FAQ ]

Posted by bimmernut on August 07, 2001 at 22:12:16:

In Reply to: Axle Ratio? posted by C Gordon on August 06, 2001 at 11:05:27:


What does a smaller or higher rear axle ratio change? What difference does it make? I'm sorta curious since I read and hear people talk about it, but never realy describe the benefits of a smaller orlarger ratio. Any info would be appreciated. Thanks in advance.


I recently changed out my stock 2.93 differential for a 3.73 differential on my 93 740iL. I've also added the Dinan chip for the engine. The total effect is about 1.5 seconds off my 0-60 times and 3-5 mph improvement in my 1/4 mile runs. I used the GtechPro to test. Acceleration is much better obviously. It runs around 3000 rpm at 70-75mph, up about 500 rpm. I investigated several different ratios using a Excel spreadsheet before going with the 3.73. Dinan offers a 3.64. Gas mileage is about 1 mpg less, maybe because of the aggressive way I've been driving and testing it. I also added limited slip with 50% lockup. Acceleration through and out of curves is substantially improved. There is a little more gear whine, but the installer thinks this can be fixed with a different weight gear oil. He's looking at that this week.

The other improvements that will help and I'll probably do next year are the exhaust and replacement of the torque converter. Even with the new differential, the initial launch is not as quick as I'd like due to the stock lockup occuring at 1950 RPM vs Dinan's converter's 2650 rpm. This puts you further up into the torque curve before it launches on aggressive starts. Casual starts would function the same as stock.


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