300hp Is Fast
Oct 5th, 2008 by Micah Tillman | 6 Comments |
Or so claims the announcer on a new Mercedes C-Class commercial.
Last I checked, horsepower was a measure of torque (power), not speed.
More hp might get you to a higher speed quicker, but in and of itself it’s not fast any more than yellow tastes good.
yellow tastes good?
Yellow is delicious.
I actually think that might make some measure of sense. (But I could be wrong)
Doesn’t Power = Force X Time?
If you kept wieght a constant, (as it basically would be in a car) wouldn’t increased horsepower translate into increased speed?
Torque = rotational force
Horsepower = [torque * RPM] / 5252
Therefore, 300HP…at what torque, and at what speed? Horsepower changes drastically as you drive, so it’s very misleading to give one single number. Any car can reach 300HP as long as the torque curve doesn’t decrease faster than the RPM increases.
Power is equal to force times velocity and engine horsepower is often estimated by measuring velocity after a quarter mile and doing the calculations with the car’s weight. Deep Thoughts Jeff is more or less correct. Holding weight (and aerodynamics of the car and potential losses of energy, such as engine friction) constant, the horsepower of an engine does indeed determine how fast the vehicle can go. Jeff Stallard is correct that the horsepower of the engine is not a constant and the particular horsepower that is needed for this to be true is the horsepower when the vehicle is at its top speed, which is not necessarily its peak horsepower (though it usually is). By the by, in all engines, the torque curve does decrease faster than the RPM increases. Most engines have peak horsepower less than 300 HP and peak horsepower is usually what is advertised. Mr. Stallard might be pointing out, however, that peak horsepower can be a misleading measure. It’s quite possible to have an engine which has a higher peak horsepower than another, but much less horsepower at lower RPMs, where people normally operate the vehicle.
Note that horsepower (relative to weight) is the most important factor both in acceleration of the vehicle and in top speed. However, horsepower, weight of the vehicle, and drag on the vehicle are the only components for top speed. Acceleration, however, also requires efficient gearing due to Jeff Stallard’s whole point about the torque curve.
I said:
By the by, in all engines, the torque curve does decrease faster than the RPM increases.
I should have added eventually. There are certainly points on the curve when this may not be true, but all engines have a peak horsepower, often at full throttle.