Re: No buts...
The confusion lies in how torque and horsepower are measured. Horsepower is a derivative of torque based on a specific rpm that the torque is produced. That rpm is a specific, steady state rpm.
300 ft. lbs of torque at 3,000 rpm will be the same number regardless of the rotational mass (assuming the engine can acclerate that mass to 3,000 rpm). Engine dynos add dynamic load (force) to hold an engine, at full throttle, at the specific rpm being measured. The engine has been completely loaded down so it cannot accelerate past 3,000 rpm at full throttle. Increasing the rotational mass by the weight or intertia of a fan or a lightened flywheel does not affect this measurement in a measurable way because we are holding the engine at a steady state rpm, not accelerating it.
What reducing reciprocating mass does (even by small amounts) is allow that engine to get to 3,000 rpm quicker. So, we can deduce that reducing reciprocating mass increases the accelerative capabilites of an engine. But, the engine is still producing 300 ft. lbs. of torque at 3,000 rpm.
I'm not arguing against replacing the fan, I'm just arguing that you do not gain any horsepower by replacing the fan. This is a very common misconception. The engine WILL rev faster without that stock fan and that can lead to quicker acceleration.
Do you guys understand?
- John