Thread: S65 vs. S62
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      01-24-2013, 02:42 AM   #74
that's what SHE said!

Drives: 2011 E92 M3 ZCP
Join Date: Jun 2010
Location: OC

iTrader: (1)

Originally Posted by bruce.augenstein@comcast. View Post
Rather than get into a long discussion with you on what, after all, is a very basic point about power, let me first mention that you cannot multiply power through gearing. Only torque. A seventh grade science book will tell you that.

Next, let me give you three examples of power and torque:

1. Stock M3 at around 100 MPH in third gear, 414 HP at 8300 rpm
2. Modified M3, 414 HP at 4150 RPM, at the same speed
3. Modified M3, 414 HP at 2075 RPM, same speed

Obviously car two will need to be in a different gear so as to be at 4150 rpm, or for this example, the final drive will have to be half the stock final drive ratio, numerically speaking.

Car three needs a quarter (numerically speaking) final drive.

OK, so these three cars are cruising side-by-side at around 100 MPH. The stocker is capable of about 262 pound feet of torque at that point (per the formula), car two has to be making double that, and car three needs 1048 pound feet, again per the formula. Other than engines and gearing, the cars are identical, weigh the same, have similar rotational inertia at that point, blah blah blah.

So everybody floors it, and what happens at that instant?

The cars stay dead even is what happens. Granted, the stocker has to shift a split second later, but that's not important here.

What IS important is that, with wildly different gearing, wildly different engine speeds, and wildly different torque production, the cars accelerate identically at that point.

They do this because thay are making the same horsepower, and horsepower is the great shorthand in this context.

As I've mentioned, you can mess about with torque at the drive wheels (and I did for years), but there's no need. Horsepower is the great simplifier.

Yes. Let me ask again: What in God's name is linear power delivery, and how does it help with traction.

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.

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.

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.

Last edited by e1000; 01-24-2013 at 02:51 AM.