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Re: Do the calculations (archive)
[ Follow Ups ] [ 5-series (E28) Message Board ] [ Msg. Board FAQ ]
Posted by WH on November 12, 2001 at 21:43:31:

In Reply to: Do the calculations posted by Chris Graff on November 12, 2001 at 11:08:39:


Now, if you want max speeds in each gear, then adjust the equation (use 6.2k rpm). BTW, you will max out the car with a 3.25 and C/R right at it's top speed, no like WH says...take a look. Your car will be aero drag limited at red line in 5th for top speed. (Remember that a tad over 140 (like 141 or 142) is the actual top speed of the dirty engine with euro aerodynamics, i.e., small bumpers). This is without a chip to raise the rev limit (which is between 6.2k and 6.4k on a stock chip, as from the test reports I've read it wasn't an exact science...don't ask me why).

With C/R, 3.07:
1st: 40 mph
2nd: 62 mph
3rd: 84 mph
4th: 118 mph
5th: 149 mph

With C/R, 3.25:
1st: 38 mph
2nd: 59 mph
3rd: 80 mph
4th: 112 mph
5th: 141 mph

With O/D, 3.25:
1st: 37 mph
2nd: 64 mph
3rd: 100 mph
4th: 141 mph
5th: 174 mph

With O/D, 3.73:
1st: 32 mph
2nd: 56 mph
3rd: 88 mph
4th: 123 mph
5th: 151 mph

Notice how 1st gear with a 3.73 at 6.2k rpm becomes a stump puller? You reduce it's speed range compared to the C/R. The reason is that 1st in a O/D tranny is a lower gear than 1st in an C/R tranny. The good thing for C/R tranny is that the gears are spaced closer together, meaning that you for a given speed range you have more chance to be in the optimal gear. For europe with 100+ highways, the O/D was a godsend. In the US, where you don't see much over 80 or 90, the C/R is effectively the best tranny, coupled with diff between a 3.07 and a 3.25. If you're in Montana, stick with the 3.07, if you're in Jersey, the 3.25 will make life much easier. :-)

Hope this helps.


I was using my E12 M535i for my comparision... Max hp is made around 5700rpm not 6200. So using the 3.07 rear will give best results (ie 5700rpm yeilds about 137.5mph). But, I've had my car at 5800-5900rpm before or about 140mph.

I don't think a E12 M535i could turn 6200rpm in top even using the 3.25 rear end.

WH

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