!#7# Torque Vs Horsepower - Which is More Important?

!±8± Torque Vs Horsepower - Which is More Important?

You've probably heard various racers and engine builders/tuners talk about torque vs HP. Some say "torque is what moves the car", others say HP is all that matters. Well, you'll have to put me in the latter camp, because HP is the most important. Torque is how much twisting force you are putting on the drive shaft, typically measured in ft lbs. Horsepower is multiplying this twisting force by RPM (how fast you can keep applying this force).

If we didn't have gears, than torque would be more important. That's because in any 1 gear, the torque peak is where the car accelerates the quickest, producing the highest Gs. The torque peak can be important for launching the line, but after that HP is all that matters.

I'll try to illustrate with some numbers. Gears are torque multipliers. You can get most any torque you want, if you are willing to give up RPM. Say you have 400 ft lbs at 3000 RPM (228 HP) and 350 ft lbs at 6000 RPM (400 HP). If you stay in 3rd gear, you could get .4 Gs acceleration at 3000 (lets say 60 MPH) and .35 Gs of acceleration at 6000 (120 MPH). However, if you shifted 1st gear and put that 400 HP to work at 60 MPH, you could get, say .7 Gs of acceleration. You may accelerate the quickest in any 1 gear at the torque peak, but you will accelerate quicker in a lower gear at the HP peak.

Racing is all about quickest acceleration to get to the highest speed. Gears let you keep the acceleration high by keeping the engine in its highest HP range. For example, if your engine has peak HP at 6000 RPM, but pulls strong to 7000 RPM, you would probably want to shift at close to 7000 RPM, so when the revs drop back to, say, 5000 RPM, you are still in a high HP range.

Let's try some real examples, using Drag Racing Simulation Software. We'll try shifting to keep the engine around the torque peak, then letting the computer keeping the RPMs around the HP peak.

Condition Pk Tq Pk HP ET MPH Shift RPMs

Keep Engine at Tq Peak 270 274 13.43 99.46 4700

Computer keeps Engine at HP Peak 270 274 12.66 106.81 6800

Computer keeps Engine at HP Peak 270 268 12.60 107.74 6950

(broader HP peak)

Standard Power Curve

You can see the performance is much better when you keep the engine in the high HP range (12.66 ET) as opposed to the high torque range (13.43 ET). The graph below shows how keeping the engine in a higher HP range in lower gears produces higher acceleration rates.

To summarize, it is HP through the correct gear ratio which produces best performance. If you are building an engine, you want the highest average HP through the RPM range you will be using. For a circle track car where you don't shift, this can be a very broad RPM range. For drag racing with a high stall converter or very narrow ratio transmission, this may be a very narrow RPM range.