 |
 View all Articles & Blog Entries
How to calculate your car's horsepowerSaturday, January 21, 2006 10:13 PM EST by Gee
|
You've just read that a certain car makes 250 lb-ft of torque at 3000 RPM. Sure that sounds great, but how much power is that? You may be surprised to find out that the amount of horsepower can be calculated from the torque value using a very simple equation: (torque x engine speed) / 5252 = hp
So, if your car makes 250 lb-ft of torque at 3k RPM, then it is producing (250 x 3000) / 5252 = 143 horsepower at 3k RPM. Easy huh? Are you wondering where this magic number 5252 comes from?
This number is actually a constant derived from combining several different conversion factors together to get from lb-ft of torque to the horsepower unit we all know and love. To get this number, we need to do a little math :-O
Horsepower is measured in ft-lbs/s (foot-pounds per second) and the definition is 1 horsepower = 550 ft-lbs/s. Since torque is measured in lb-ft (pound-feet), we are just missing the "per second" part of the unit to get torque from horsepower. You can get this time measurement by multiplying by the engine speed.
Since engine speed is measured in RPM (revolutions per minute), we simply need to convert this into radians per second. Why radians? Because radians are a dimensionless unit and all we need is the "per second" term to get from horsepower to torque. The first part is easy. To convert from minutes to seconds, we just divide by 60. (Revolutions per minute) / 60 = (Revolutions per second). Now to get the radians part we need to think back to geometry. One revolution is 360 degrees, and the circumference of a circle is 2 x π x r, so there are 2 x π radians in a revolution. What does all this mean? It means, to get from revolutions per minute to something per second, we just multiply the engine speed in RPM by (2 x π) / 60. This comes out to a value of 0.1047198 radiands per second, or just "per second".
Now, if we combine this by dividing 550 ft-lbs/s by 0.1047198 rad/s, we get 550 / 0.1047198 = 5252, which is used in the equation above to convert torque to horsepower! ( ie, from pound-feet to foot-pounds per second ).
Ok enough of this math. Want to really gain some hp? Find "air intake systems" and "exhaust systems" on MODsearch.com from dozens of different vendors.
 Previous | Comments(2) | Index | Next
 del.icio.us |  digg this |  RSS
302 with close chamber 71 comp cam 280h holler 650 intak edelbrook rpm
Posted by samuel on 9/14/2007 11:56 AM
| ку ку
Posted by Anonymous on 1/6/2008 10:26 PM
|
|
|  |
