[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index] Correlation, Torque & Power
I hope the following can be to some benefit for some of you, I was certainly thrilled when I first realized the simple correlation between torque and power. If you have a torque of 200 Nm @ 6000 rpm, this can be geared down to 3000 rpm providing a torque of 400 Nm. That is more power than 300 Nm @ 3000 rpm, even though this is higher torque. (remember pulleys and lever arms from the physics class?) The effecient torque on the wheels is therefore proportional with torque and engine speed, provided suitable downgearing. The maximum torque of an engine will only give an indication of the power at low or medium engine speeds. What really matters is how much power the engine gives at ALL engine speeds. An engine's torque and power with corresponding rpms gives two points on the powergraph only, while the powergraph for all engine speeds is more interesting. The basic formula for calculating the power is: torque(Nm)x(Rad/s)= power (Watt) In practical terms using rpms and hp it is: torque(Nm)x rpm x 0,00014242 = hp (the constant is 2pi/60/1000 x 1,36 (radians to rpm, and watt to hp) I have made a table for the audi S4 turbo, which has 350 Nm @ 1950 rpm and 230 hp @ 5900 rpm. Rpm Nm Hp 1000 200 28 1500 260 56 2000 350 100 2500 345 123 3000 330 141 3500 315 157 4000 300 171 4500 292 187 5000 288 205 5500 280 219 6000 269 230 6500 240 222 7000 215 214 As you can see, the S4 with the high torque at low rpms gives 100hp at 2000 rpms, and a hefty 170 hp at 4000. Whether it has 230 or 240 hp at 6000 rpms doesn't really matter as long as the power is what it is at all other revs. Hans Sandvika, Norway 92 S4 Avant 95 Yamaha 600 XTE (XT denotes extra torque :-)
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