[quote name='ds968' timestamp='1349209856' post='133288']
btw, I just spoke to him, he was in 3rd gear and I was in 4th , though I sense even if we were both in 3rd, and I had the AC off, yada, yada .. the 964 is still quicker by virtue of its torque sustainability ..
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Just because you're both in 3ed doesn't tell you enough. The force between the tire and the road which goes into the F=ma equation to see who accelerates the fastest comes from several factors. You start with the engine torque, multiply it by the 3ed gear ratio, then multiply it by the final drive ratio and then divide it by the radius of the wheel (in feet if you are using ft-# for the torque values). If you know the weights of each car as tested, divide the above calcs by the weight of the car which will result in two numbers, one for each car, which is proportional to the acceleration of the car. If his ratios don't mutiply out as big, or if his tire OD is much larger, or the weight much different, you might still show pretty well. Of course, as you said, since his torque sustains it's high value longer into the upper rpm range, you may initially pull ahead only to have him overtake you.
Someone who knows these ratios should do the math just to see how much of a shot you have at least at the initial "start". If you want to get a little more accurate, since you are both starting at the same speed, say 40 mph, you need to get the torque value for each engine at the rpm corresponding to the "start" mph.
And, yes the equation should include the effort it takes to accel the rotatinal inertia of the engine/drivetrain. These aren't so easily known, thus calculated/compared.
The math gets a lot more difficult if you want to run a simulation of the whole race. I know there are some other engineers out there who might remember this better, but if memory serves, you'd have to take the integral over time having each torque value for that instant in time for where the engine is in its rpm range.
