Torque and power

Not even sure how I got to this thought, but I can't sleep anyway.

The "which is more important.. torque or power" debate is popular in shop talk, and if you ask me, pretty dumb. I believe there's even the saying, maybe even from Carroll Smith himself, "horsepower sells cars, torque wins races" or something to that effect. The two are so closely related with speed it makes absolutely no sense to compare the two as separate entities. Let's go over some simple concepts though.

With a large enough gearing, I could turn a crank with my feet and make more output torque than a Formula 1 engine. That doesn't do me any good however, as I'd never be able to turn the crank at that load, at a high enough speed to make anything of it.

To accelerate an object (read: car) to a given speed requires an energy input. Pure and simple. To get a car up to 100 mph requires a fixed quantity of energy transfer, I don't care how you do it. You want to get this done in the shortest time possible. Work over time is power. The quicker you want to get to 100 mph, the more power you need.

There is however also an acceleration requirement to get to a given speed in a given amount of time. That requires a fixed value of average thrust at the tires, and thus torque. If I had a really high power engine with extremely long gears, it would do me no good as I'd never produce the required thrust to do anything useful.

To achieve maximum acceleration, there is an engine power and WHEEL torque requirement, and the two are related by gearing. That's all there is to it. Keep in mind of course, if you have a high power motor and you're not developing enough thrust, you can always gear it down to bump the torque up. You can't however pull power out of your ass.

Another way to think of it is as such. To keep a car going 100mph you have to overcome some amount of drag. Drag force itself lends itself to a torque requirement... but force times velocity is a power requirement.

Or, think of what the race engine is basically required to do. You want to burn the most fuel as quickly as possible, and efficiently as possible (without blowing up). You want to be able to release as much as that chemical energy in the fuel as possible in the shortest amount of time (again, maximizing how much mechanical power is made). To that point, to burn more fuel, you generally need more air. As a corollary, for a given mass flow rate of air there's only so much fuel you can burn, and so much power you can extract. For you FSAE folks, as a fun challenge, find the maximum mass flow rate of air you could possibly hope for, through a 20mm restriction. Find how much power can generally be extracted per unit mass flow of air, and then find out the most power you could hope to get out of it.

It's fun comparing the maximum theoretical power output of one of those restricted motors with how much some teams claim to make, ie the guys who say they can make more. It is good to know though, what max RPM your engine should be choking the restriction at. I really wish we'd had the time to get some cams made up designed around that. Oh well.

In any event, going by peak values, as is typical, is as meaningless in my opinion as calling a car "tight" or "loose." Really doesn't tell you anything. Area under the curve seems like it would be the more important parameter.

Edit - Was originally gonna include some thoughts on the claims of some engines to "give tires time to rest between cylinder pulses and regain grip" but I'm saving that for another day.