Thread: S65 vs. S62
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      01-24-2013, 02:19 AM   #73
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Drives: Legacy GT - 13.704@99.39
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Originally Posted by MKE_M3 View Post
horsepower = Torque * RPM / 5252

Power to the wheels is horse power * mechanical advantage.

To get how much power the car is putting down, you need torque and gearing. That is science.
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.

Originally Posted by MKE_M3 View Post
Yes. Let me ask again: What in God's name is linear power delivery, and how does it help with traction.