Quote:
Originally Posted by Bob Bidonde
It is torque that counts. Torque accelerates and horsepower sustains speed.
|
Not quite. An engine produces only torque. Horsepower is calculated from a formula which factors in RPM, or how fast torque is produced. A dyno only measures torque output and RPM. The formula is torque times RPM divided by a constant which is 5252.
Peak torque for a stock A is 128 ft. lbs. at 1,000 RPM which calculates to 24.4 HP. At 2200 RPM, torque is down to 95.5 ft. lbs. but horsepower is up to 40, which is peak for a stock A (factory rating). An engine's maximum efficiency is at peak torque RPM. Torque drops off above that point, but since it is produced faster (higher RPM) horsepower goes up, to a point.
Picture a 128 lb. person standing at the end of a one foot long bar attached to a dyno. He/she is producing 128 ft. lb. torque, but zero horsepower. Now imagine the bar is a crank and the person has enough strength to turn it at one RPM. The result is .0244 horsepower. If he/she could turn the crank at the rate of 1,000 RPM while still exerting 128 ft. lbs. of torque, they would be putting out 24.4 HP.
So an engine designed for maximum efficiency (air flow) at low RPM will have peak torque at low RPM and horsepower will be a low number. Build that engine for max air flow at high RPM and peak torque will be at a higher RPM, and horsepower numbers will follow. So if a Model A had the same peak torque of 128 at 5,000 RPM, peak horsepower would be 121.9.
So, it's a little more involved than saying torque does this and horsepower does that.