| You've probably heard various racers and engine | | | | but pulls strong to 7000 RPM, you would probably |
| builders/tuners talk about torque vs HP. Some say | | | | want to shift at close to 7000 RPM, so when the |
| "torque is what moves the car", others say HP is all | | | | revs drop back to, say, 5000 RPM, you are still in a |
| that matters. Well, you'll have to put me in the latter | | | | high HP range. |
| camp, because HP is the most important. Torque is | | | | Let's try some real examples, using Drag Racing |
| how much twisting force you are putting on the | | | | Simulation Software. We'll try shifting to keep the |
| drive shaft, typically measured in ft lbs. Horsepower | | | | engine around the torque peak, then letting the |
| is multiplying this twisting force by RPM (how fast | | | | computer keeping the RPMs around the HP peak. |
| you can keep applying this force). | | | | Condition Pk Tq Pk HP ET MPH Shift RPMs |
| If we didn't have gears, than torque would be more | | | | Keep Engine at Tq Peak 270 274 13.43 99.46 4700 |
| important. That's because in any 1 gear, the torque | | | | Computer keeps Engine at HP Peak 270 274 12.66 |
| peak is where the car accelerates the quickest, | | | | 106.81 6800 |
| producing the highest Gs. The torque peak can be | | | | Computer keeps Engine at HP Peak 270 268 12.60 |
| important for launching the line, but after that HP is all | | | | 107.74 6950 |
| that matters. | | | | (broader HP peak) |
| I'll try to illustrate with some numbers. Gears are | | | | Standard Power Curve |
| torque multipliers. You can get most any torque you | | | | You can see the performance is much better when |
| want, if you are willing to give up RPM. Say you have | | | | you keep the engine in the high HP range (12.66 ET) |
| 400 ft lbs at 3000 RPM (228 HP) and 350 ft lbs at | | | | as opposed to the high torque range (13.43 ET). The |
| 6000 RPM (400 HP). If you stay in 3rd gear, you | | | | graph below shows how keeping the engine in a |
| could get .4 Gs acceleration at 3000 (lets say 60 | | | | higher HP range in lower gears produces higher |
| MPH) and .35 Gs of acceleration at 6000 (120 MPH). | | | | acceleration rates. |
| However, if you shifted 1st gear and put that 400 | | | | To summarize, it is HP through the correct gear ratio |
| HP to work at 60 MPH, you could get, say .7 Gs of | | | | which produces best performance. If you are building |
| acceleration. You may accelerate the quickest in any | | | | an engine, you want the highest average HP through |
| 1 gear at the torque peak, but you will accelerate | | | | the RPM range you will be using. For a circle track car |
| quicker in a lower gear at the HP peak. | | | | where you don't shift, this can be a very broad RPM |
| Racing is all about quickest acceleration to get to the | | | | range. For drag racing with a high stall converter or |
| highest speed. Gears let you keep the acceleration | | | | very narrow ratio transmission, this may be a very |
| high by keeping the engine in its highest HP range. For | | | | narrow RPM range. |
| example, if your engine has peak HP at 6000 RPM, | | | | |