I'm wondering about some of the horse power figures that are frequently used arouund this board. For instance, the Raptor has 38hp, the DS650 has 42hp, the 450s or ES have 23hp, the Rancher has 21hp, the 400ex has 27hp, and the stock 250R has 32hp. There is one horsepower figure that just doesn't sound right compared to the rest, provided they are right. Thats the 38hp credited to the SP500HO, and Scrambler 500. Are we to believe that the Polaris 500's make the same hp as a Raptor? Remember I'm talking hp not torque. I guess its really like that famous person in history said, the bigger the lie, the the easier people will believe it. I think it went something like that anyway.

 

Bob:
Not sure if you know this already or not-I just learned it the other day in fact! Anyway, a simple equation to remember for horsepower is as follows:

HP=(torque x rpm)/5252

This works for all engines, whether large automotive, or atv's. I'm not exactly sure where the "5252" comes from, it's just a "constant" variable so to speak. Anyway, if you know even two parts of this equation, you can easily find the third through a little algebra.

Hope that helps, Best of Luck!

Mike

 

Remember that the horsepower curve or more importantly torque curve has a lot more to do with performance than peak horsepower. I can guarantee that peak horsepower is what is being quoted, however it doesn't do much if a motor produces that in a narrow rpm band then drops off. The equation cowboy quoted is absolutely correct, horsepower is nothing more than the rate at which torque can be put to work. That's why diesel engines have low horsepower ratings but huge torque ratings, they rev low. No one would suggest that a 350 chevy producing 300 horsepower will pull nearly as much as a cummins diesel producing 170 horsepower. The difference is in the 300 ft/lb torque made by the chevy vs. the 420 made by the cummins. The diesel will be slower but will pull more.

 

Your formula may be correct, cowboy, but . . .

Engines produce their maximum horsepower at a higher rpm than they produce their maximum torque.

If you examine overlaid horsepower vs. rpm and torque vs. rpm curves, you will notice the horsepower peak occurs at a higher rpm than the torque peak.

Thus, your forumla yields the horsepower value at the torque peak rpm; however, the formula does not yield the maximum horsepower, occuring at a higher rpm value.

Similarly, were you to substitute the maximum horsepower value, and the rpm at the HP peak, in your formula, you can calculate the torque produced at that point--less than the maximum torque produced at a lower rpm.

Summary: Although the horsepower produced at the torque peak can be calculated with the formula, that figure is less than the maximum horsepower the engine can produce, because the horsepower peak occurs at a higher rpm than the torque peak.

Tree Farmer

P.S. Horsepower figures are entered on "Manufacturer's Certificates of Origin" (or, Manufacturer's Statement of Origin) for motor vehicles. What does yours say? I do not know how this figure is derived; by formula ("taxable" horsepower) test (SAE?), or whatever.

T.F.