Quote:
Originally Posted by mrray13
Wasn't needed. No offense was taken. If I'm wrong on how it works, I'm wrong, no biggie. I'll argue the results, as I have dyno sheets in front of me that back up what I'm saying.
Besides, there's nothing wrong in learning. Again, I'll argue the horspower can't truly be measured, it's derived from torque. All my reading says this in one way or another. It's a mathmatical guess, based off torque, which can be measured. For while we have a constant to relate to getting horspower from torque/rpm, that constant is just an accepted standard, based on what a person judged the amount of force a horse could generate. I've not seen anything that says that constant was ever verified, but rather, I have seen text that states there are different opinions on just how much that force could/should be.
Then again, I could be wrong, lol.
BTW, thanks esperman  |
Horsepower is an exact value, not a guess, that is based off an amount of work done over a given time period.
1 HP= 746 Watts = 550 ft-lb/s
A typical chassis dyno uses a roller of known inertia, and the dyno simply has to compare how fast the rollers are accelerated and determine the power it would take to accomplish that. The final numbers are based on the calibration values for the particular dyno.
HP=torque (ft-lbs)*rpm/5250
Note that HP is a function of force (torque) and time (rpm). The higher the rpm (shorter time interval) for a given torque, the higher the hp. So a chassis dyno does not directly measure hp, it measures the rate at which the roller is accelerated.
An engine dyno uses a water brake attached to a load cell to measure the resistive braking force (lbs), then based on the distance from the center (ft) you determine how many ft-lbs of torque are output by the engine. Then you use the formula above to calculate the hp based on rpm.