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#27817

Mark Sink
Participant

TQ is for pulling stumps out of the ground.

HP = TQ x RPM / 5252

The question is too complicated to answered completely, because we’d need to have both complete power curves just to start.  But the short answer is, you want HP.

The fact is that TQ as a number, by itself, doesn’t tell you much.  What is 500 ft/lbs?  It’s a fat guy jumping up and down on the end of 1 foot wrench connected to a crankshaft.  That’s not going to win any races.  You need more information than just TQ.  The missing number is Time. How quickly can he jump up and down on the wrench? one time per minute… 1 RPM or 16,000 RPM?

That’s what HP tells you. It’s a number that takes both TQ and TIME into consideration, accounting for both and allowing you to decide which is better.

Motor A. makes 5 ft/lbs @ 13,800 RPM = 13.13 HP

Motor B. makes 5 ft/lbs @ 16,500 RPM = 15.7 HP

Motor B makes the same amount of TQ, but at an RPM that is 20% higher, 16.5K vs 13.8K.  It also makes 20% more HP, and because it can rev 20% higher, it can run gearing that is 20% higher… which is where TQ really comes into play.  NOT how much TQ the engine makes, but how much TQ actually makes it to the ground.

Imagine Motor B, it’s generating the same 5 ft/lbs of TQ, but at 20% faster intervals AND running 20% higher gearing.  Now, this is not an real world example (Motor A / Motor B)  I don’t know what levels of power they make at what RPM.

If Motor A is running a 10/82 gear, Motor B can run the SAME track with a 98.4/10!

Muscle cars pay a price for that low end grunt in engine weight.  Its very difficult for a normally aspirated car to make lots of torque without forced induction, or more cubic engines.  But adding RPM is almost free. Not increasing compression, not adding weight, just doing things faster!

In the 3.0L V10 days of F1 cars, they were revving to 19,000 RPM, making lets say 850 HP.  If that 850 HP came at 19,000 RPM, then they were also making only 234 ft/lbs of TQ at 19,000 RPM.  When they upshift, revs dropped maybe 2,000 RPM.  That means the fastest circuit racing cars in the world were driving around producing TQ levels found in a mid-sized ford pickup.  Engine TQ doesn’t win races. Small, light weight, high revving engines win races.

 

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