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Originally Posted by earlyapex
Well if we are going to dig into details, we should get them right - horsepower is actually (torque * RPM) / 5252.
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But if you read again, I never said different. I did, however, specify a definition for power, which is not the same as (and is a generalization of) horsepower.
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And you can't *measure* horsepower on a dyno. Dyno's measure torque. Horsepower is a mathematical calculation derived from torque based on RPMs and a constant.
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Right, yep, very aware of how a dyno works. Nevertheless, a dyno is a tool that provides horsepower as part of its ouput data. It therefore measures horsepower. Semantics of how it does so are important, but the fact that it does so remains true regardless of those semantics. If someone asks, "How do I measure my car's horsepower?", a reasonable answer is "Use a dynomometer.". I never meant to imply anything other than that inarguable fact.
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I, and several other, posters may be misreading you, but your original post seemed to imply that you thought horsepower somehow "took over" from torque at a certain RPM to provide acceleration.
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Sorry for the confusion, but my point was that the car will not provide best performance if you shift at 4k RPM. Maybe no one was saying so, but I wanted to make sure no one got that mistaken idea from reading the thread. I should not have referenced power in my post to begin with, that was my error.
Another way to look at it is, suppose you put a CVT in an M3 (a stong capable CVT, say). The car would perform better if the engine were brought to 4k RPM and held there, than if the engine were brought to 8k RPM and held there. However, since we don't have a CVT, we must rev the motor past the RPM where peak torque is made in order to get best acceleration. The reason is, we want to have the torque remain near peak once RPMs fall back down to pick up the next gear ratio. The beauty of the M3 engine, then, is that it allows you to keep increasing RPM way past peak (torque curve stays relatively flat) - in preparation for the next gear, as I say - without giving up too much in acceleration vs. if you could instead keep the RPM at 4k and simply change the ratio instead.
(And before someone says it, I realize 4k and 8k RPM are arbitrary and don't necessarily represent exact optimal/least-optimal figures, I was just using the previously established examples.)