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      01-12-2013, 11:53 AM   #50
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Drives: 2011 328i LMB 6MT
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Quote:
Originally Posted by BEAR-AvHistory View Post
The math is nice & will put you in the ballpark but it does not include one very important variable Time. As RPM increases so does the amount of time it takes to gain additional RPM.

So in the case of a turbo with a redline of 7K vs. a shift point of 6K/6.3K pure math might suggest go at 7K. If the time it takes to get from 6K to 7K out weighs the mechanical benefits of a redline shift then you need to shift earlier.

Only two ways to figure this out. Various shift points at the same track on the same day or what the pros do with their onboard systems use an accelerometer to optimize the shift point.
No, that equation includes everything you need to know. Acceleration is defined as the change in velocity per unit time. "The amount of time it takes to gain additional RPM" that you speak of is simply another way of saying "acceleration".

So what you said can be summarized by one sentence: "At higher RPM the acceleration drops". This is the same thing as saying that at high RPM the torque drops off. This doesn't have to be the case, although for most engines it's true. So you are saying that sometimes the torque drops too much at high RPM that it could be preferable to upshift, thereby taking a hit in gear ratio but increasing the torque at the crank. This would be true if either the gear ratio is fairly narrowly spaced, or the torque drop is extreme. That's exactly what driverman's post explains.
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