Thread: S65 vs. S62
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      01-24-2013, 12:31 PM   #80
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Originally Posted by e1000 View Post
Your example is confusing because an engine producing more torque at a lower RPM, that could continue to make that torque across a wide rpm range, will have a higher horsepower rating.
Not to be a dick about it, but so what? If it makes it less confusing, let me postulate that the 4150 rpm engine has a red line of 4200, and the 2075 engine redlines at 2100. In addition, each engine is at its power peak, and they all have the same shape power and torque curves. It makes absolutely no difference, however, because I was specifically talking about what happens at the instant those three cars floor it, and not what happens at any other instant.

Originally Posted by e1000 View Post
You are right in that horsepower IS the shorthand that generally summs up an engine's performance, but you can't just throw out gearing like it doesn't matter. The truth is, if the analogy is understood, we would also have to concede that in order for those engines to produce that torque at those rpm's and have that HP rating, they would all have to essentially shift very very soon.
Again, so what.

And while we're at it, I wasn't talking about how peak power more or less sums up an engine's performance. I was specifically pointing out that, at any given speed, horsepower and weight dictates how a car will accelerate at that instant, and torque, gearing and rpm are completely immaterial. Those three examples demonstrate the point vey adequately.

Originally Posted by e1000 View Post
Why does gearing still matter? Gearing still matters because given the same exact car (6MT M3 vs DCT M3), you can have one car consistently win. Let's take for a moment that the 6MT was being driven by a machine that could reproduce accurate shifts every single time, with zero time between shifts. It would still lose to the DCT car due to the gearing and how the torque curve is then translated to the road. Any advantage in to the wheel torque of the shorter 6MT first gear is negated by the available traction, and then it's all on the DCT's favor.
Of course gearing matters across an engine's operating range - but again, my examples illustrate how power and weight are what dictate acceleration at any given instant, and for the umpteenth time, torque, gearing and rpm are immaterial in that context.

In your example of auto vs stick M3s in a drag race, let me suggest that both cars are at a sprayed drag strip, with track temps at, say, 90 degrees or so. I'm suggesting that to get away from what I consider is beside the point in this general discussion, and stick to the main points, which are gearing and shift speeds - not traction.

In that context, I'm thinking the stick car will have a minor advantage over a quarter mile (assumimg optimum launches for each vehicle), because it will launch harder, and will spend more time under power during the run because of the zero-length shifts.

No biggie. Just an observation.


PS - In general, gearing tends to be a little less important than folks think in terms of acceleration. If you change the M3's final drive from a 3.85 ratio to, say, a 4.11, the car will clearly be able to put more torque to the drive wheels at any given engine speed, but that torque will be delivered at a lower vehicle speed.

The net effect is that the geared car will have the early advantage off the line, but when it shifts to second gear, the stocker will now have an advantage because it's still in first, and is now making more power (and of course more torque to the drive wheels) than the geared car. Then it has to shift and the geared car now has the edge...and so on.

Because the geared car has the early advantage in each gear, there are ET implications, given perfect traction, but trap speeds won't change much, because average power over the quarter mile won't change much, and it's power and weight that tend to govern trap speeds.

Last edited by bruce.augenstein@comcast.; 01-24-2013 at 12:40 PM.