How Horsepower and Torque are derived

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How Horsepower and Torque are derived

Postby Larry Jowdy » Thu Dec 31, 2009 8:48 am

The following formula's and examples show that Horsepower and Torque cross at exactly 5,252 RPM's on any engine


The formula for determining horsepower is:

horsepower = rpm x torque divided by 5252 (5,252 is the constant)

For example: Lets say that an engine produces 150 lb's of torque at 5,252 RPM's
5252 rpm's x 150 (torque) divided by 5252 (constant) = 150 Horsepower

The formula for determining Torque is:

Torque = Horsepower x 5252 divided by RPM's

For example:
Lets say that an engine produces 150 HP at 5,252 RPM's
150 (horsepower) x 5252 (constant) divided by 5,252 (rpm's) = 150 torque

By working the formula both ways, you can clearly see that 5,252 RPM's is where Torque and Horsepower will be exactly the same number.

These formula's also work on a diesel engin however most diesel engines will explode at 5,252 RPM's:

Another example: My motorhomes diesel engine produces 400 HP at 1,500 RPM's

400 HP x 5252 divided by 1500 (rpm's) equals 1,400 lb's of torque
(spot on to the engine manual)

1400 torque x 1500 rpm's divided by 5252 equals 435 HP.
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