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      06-03-2013, 05:09 PM   #41
CanAutM3
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Quote:
Originally Posted by swamp2 View Post
Here are the actual acceleration profiles. Almost identical except in 1st gear.
Thanks for doing this

If we assume DCT, why the interruption in acceleration on gear shifts? Also, why so much wheel spin and lost acceleration going into 2nd? If the car was able to pull 1g in first gear without losing traction, there is no reason it cannot pull 0.75g in second gear. I am guessing that we don't see benefits of the gearing due to assumed shift times and tire slippage shifting into 2nd...

Let me explain why I selected those gear ratios. I reduced 1st gear because I don't think the tires would be able to sustain 1.2g in real life, so I reduced it to slightly above 1g. I also adjusted the spacing between gears 2 to 6 so that the engine always remains in the power plateau, which should yield better theoretical acceleration.

Quote:
Originally Posted by swamp2 View Post
Generally results across gears are relatively insensitive to such changes, whereas some individual results will show sensitivity. Again it all comes down to power, peak performance depends on peak power, which means torque + gearing. If you just focus on power, gearing basically drops from the equation (given it is not something entirely unreasonable for the car).
Agreed that it all comes down to power. Peak power is a great way to quickly assess overall performance. But ultimate performance is about average power produced during an acceleration run, not only peak power. IMO, this is why the power plateau will make the M3/M4 performance impressive.

Quote:
Originally Posted by swamp2 View Post
Here is the summary of numbers. No practical change in 1/4 mi time nor trap. Surprised? I'm not. This is very much like the final drive mod debate! Did you follow one or more of those?...
Well this is relative. Small changes in gearing, where the average (or total) power produced during the whole acceleration run is unaltered, will not have an impact on trap speed or ET. However, if by optimizing the gearing, more average (or total) power can be produced for the same acceleration run, in such case, ET and trap speed will be better. The more extreme example is imagining doing a run in only one gear...

Last edited by CanAutM3; 06-03-2013 at 07:06 PM..