Torque vs Horsepower: Clarifying the Difference

[jmnew51]

I had a dispute with a fellow on the subject of automobiles.
He insisted that torque is the force that gets you across the finish line in a race.
I insisted that torque is only part of the equation and that horsepower is what does the work, as horsepower or kilowatts, etc. is a fuction of torque and r.p.m. Torque is basically a static force, right? I would just like some clarification on this.

I may be totally wrong, but please let me know either way.

Thanx for listening.

Jim

 

[rcgldr]

You're correct. Torque is almost meaningless, since as you mention, you can have a static torque where nothing is moving. The key factors for a car engine are peak power and the torque versus rpm curve. The flatter the torque versus rpm curve, the wider the power band. In the case of race cars with very fast shifters and lots of gears, such as a Formula 1 car, the power band doesn't need to be that wide, so there's more focus on maximum power at the cost of a wider powerband.

Rear wheel torque is related to the rate of acceleration, but being fast from 0 to 15mph isn't the same as fast from 0 to 60mph, so again, it's torque times rpm which is power that counts. Converting this into lateral components, force times speed equal power, for example, force in lbs times speed in mph divided by 375 (conversion factor) = power/horsepower.

 

[jmnew51]

Thank you Jeff for the clarification.
Maybe having more torque over a wider rpm is what he was referring to.

All in all, it's like saying that the amps is what lights the light bulb, but we know that we need the volts to push the amps through a given resistance.

I know what you mean by close ratio, quick change gearbox. My girlfreinds Mazda Miata tachs out at about 7000 rpm, and gears 1 to 5 wil take you to about 100+-mph before redline, but the engine does not develop any power till around 4000 rpm, hence the close ratio necessary. Same with sport bikes. Try accelerating in 4th or 5th gear at 2 or 3 thousand rpm.

Jim