Quote:
Originally Posted by Calum
Horsepower is torque X rpm /5252. So, torque is a component of horsepower. You can't increase one without increasing the other at a given rpm. What you want is more horsepower at the lower end of the RPM range.
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I see it this way (I'm in no way disagreeing with you, just trying to simplify it).
Torque is the measure of force and I understand why some people say that's the only thing they care about. NOW, looking at horsepower and understanding its meaning you can deduct what is torque doing given any RPM range. If you see HP curve flattening out, that's not good, you are loosing torque. If you see HP curve rapidly increasing, that is good most probably your torque is increasing. If HP curve is increasing, but not at a big rate, most probably your torque flattened out which is not bad as long as it is a healthy high number.
So even though Torque is the most important number, you can get a good idea of what torque is like if you have a curve.
In the below graph, TQ is pretty much flat, that is why you see an increasing HP curve (sine the HP equation depends on TQ and RPM, if you keep TQ constant but increase RPM at a linear rate, the HP will increase linearly).
In the other hand, in the below plot you see the TQ mostly flat up to 5000 RPM and HP curve increasing mostly linearly. Then at 5K RPM, TQ falls off. Again, since the HP equation depends on TQ and RPM, the RPM keeps increasing but TQ starts to decrease. This causes the HP curve to start leveling out and even decrease. That is what I meant, looking at the HP curve you can at least have an idea of what the TQ curve is doing.
Disclaimer: Of course none of this works with just the peak HP, but it is no good either if you only have peak TQ, you need to see the curve to be able to tell how good does a system perform.