Originally Posted by mikegarrison,Aug 24 2005, 12:55 PM

horsepower = units of power, just like pounds = units of force or ft-lb = units of torque

power = F * V, yes. You may recall that work or energy (same stuff) = F*X (where X is the distance over which the F is applied). Power is work/time. F*X/t = F*V.

In the equation HP = (Torque * rpm / constant) you see the same thing. F*X (foot pounds) * (1/t) (rev/min).

When a car first accelerates, and both velocity and force are increasing, there IS a dramtic increase in actual horsepower output from the engine. This is the HP curve you see on a dyno run. It goes up dramatically.

If you were to take the plot and multiply the force line by the mph value, you would see the result (power) start from zero and shoot up to a high value by the time the car had to shift to second. From then on it would stay pretty close to that initial peak value, dropping a bit when shifting and then ramping back up. Just like a dyno plot trac from about 6000 rpm to 9000.

However, the "invisible line" I was referring to is not the actual HP from the engine, it is the maximum HP that the engine can provide (about 240 in the case of the S2000). That is what limits the potential benefit of an gearing. The closer you can keep the engine to constantly putting out that peak HP, the more force you will have at any given velocity, and the faster you will accelerate.

Looking at the plot, the really big advantage of the shorter gearset is that it gives you better initial acceleration in first gear, and pushes you up close to the peak HP potential faster. So most of your gain is right off the line. But you get to keep that gain all the way until you rev out at 150.

So like I said, I hav a new understanding of why this is an attractive mod for drag racing. When I originally said it had very little effect, I was thinking only about the part of that plot where you are already up near your max HP, and the two lines sort of braid over each other. I had discounted the initial first gear accel because it's not important to me, without recognizing that it is very important in drag racing.

Originally Posted by jasonw,Aug 24 2005, 12:57 PM

I mainly had to point out the problem with statements like this:
Which goes beyound 1/4 mi & 0-60 races.

Originally Posted by mikegarrison,Aug 24 2005, 01:25 PM

Another reason why people perceive the gears to be such a performance boost is in "real world" driving. Let's say the two cars are driving along at 40 mph in 3rd gear. The 4.10 car will be at 4000 rpm, the 4.57 car will be at what, 4300? Something like that.

They decide to make a pass.

The 4.57 is already higher in the power band AND has a bigger torque multiplier. So he's gonna pull away from the 4.10 car -- hard.

But if the 4.10 downshifts to second, the advantage disappears or maybe even goes the other way. However, most people (even S2000 owners) just aren't in the habit of downshifting to second at 40 mph. So the car with gears will definitely feel like it has more "real world" acceleration, even though the other car (if driven like it's on a racetrack) can actually pretty much match it.

Originally Posted by Wisconsin S2k,Aug 24 2005, 12:40 PM

except for the fact that at 40mph, the geared car can ALSO downshift to 2nd.

Originally Posted by mikegarrison,Aug 24 2005, 02:53 PM

But the 4.57 will have to shift back up before the pass is complete, while that may not be true of the 4.10 car. These things are all pretty even trades. The thing that is not even is the low RPM extra pulling power of the lower-geared car. Not usually a big deal on the track because you avoid low rpms, but a bigger deal in normal driving.