The Definitive Torque vs. Horsepower post
Year after year, I keep seeing the same old debates about torque vs. horsepower. Everyone seems to have a general idea that we are referring to power, but most don't really understand the relationshi...
Forum Discussion
Look at turbine engines, they still use the same equation for hp and torque. Aircraft are rated in shp, at least helicopters.
One example is a twin engine helicopter, at 100% torque (yes called torque) it's only getting 355 ft/lbs from each engine.. or 710 ft/lbs.. that is over 100 ft/lbs less than my truck makes. I could come nowhere near to spinning the rotor enough for flight because I am over 1100hp shy of what is required.
So what's the other side? 1426 horsepower.. and that's how it flies... and a LOT of gearing reduction.
I'm a diesel guy, I like torque but it's not the only important number. Torque gets you moving, horsepower keeps you moving.. horsepower is a function of rpm, and the rate at which the torque can do it's job.
Diesel makes more hp at lower rpms, that's why it has torque and that's why they drive better, lower rpm hp/torque.
Here is another example. Let's assume the engine has a 100% flat torque curve and makes 500 ft/lbs, and is operating at WOT. So now lets only change the gearing (gearing is very important, I think we all agree). So the constants are torque, tire size (265/70R17), transmission ratio (1:1), and speed (60mph).
4.30:1 rear end: 2829 rpms 269hp
4.10: 1 rear end: 2698 rpms 256hp
3.73: 1 rear end: 2454 rpm 233hp
3.55: rear end: 2336 rpms 222hp.
Okay, so same constants.. but this time the torque required changes to 1000 ft/lbs at the wheels. Lets see what that does to hp/tq at the engine.
4.30:1 rear end: 2829 rpms 125hp/232tq
4.10: 1 rear end: 2698 rpms 131hp/243tq
3.73: 1 rear end: 2454 rpm 144hp/268tq
3.55: rear end: 2336 rpms 151hp281tq
So the same work is being done by the 4 setups, but as rpms drop the hp required increases. That's a function of gearing, but the same thing would happen with 4.30's if you slowed down and still required 1000ft/lbs at the wheels. What requirement is increasing? Hp or Tq? Or Both?
They are all putting out the same torque, but the hp changes quite a bit. Why do you think that 4.30s would be rated to tow more? The torque is the same, so all you torque is the only thing that matters people, why??
Bottom line, you cannot argue one over the other. They need each other to be effective. Yes a 300hp 10,000 rpm Honda engine can put the same power to the ground as a 300hp 2,000 rpm diesel.. but getting to 10,000 rpms is painfully slow, lots of gearing (heat) and other issues. Which one will tow better?
To everyone who is comparing personally owned gas and diesel trucks the comparison is very hard to make fair unless both rigs where rated at the same hp, and you operated both at rated rpms. If you weren't, then it's not a fair comparison. The diesel still winds because it makes more per per rpm than a gas engine, thus more power available at average rpms.
I'm a diesel guy, so I think torque is king.. if it's made at the proper rpms. Which means more hp at lower rpms, which means more torque.. Going in circles, but that's how it works. The highest torque in a useable rpms get the work done the quickest, that's explained as horsepower....
One example is a twin engine helicopter, at 100% torque (yes called torque) it's only getting 355 ft/lbs from each engine.. or 710 ft/lbs.. that is over 100 ft/lbs less than my truck makes. I could come nowhere near to spinning the rotor enough for flight because I am over 1100hp shy of what is required.
So what's the other side? 1426 horsepower.. and that's how it flies... and a LOT of gearing reduction.
I'm a diesel guy, I like torque but it's not the only important number. Torque gets you moving, horsepower keeps you moving.. horsepower is a function of rpm, and the rate at which the torque can do it's job.
Diesel makes more hp at lower rpms, that's why it has torque and that's why they drive better, lower rpm hp/torque.
Here is another example. Let's assume the engine has a 100% flat torque curve and makes 500 ft/lbs, and is operating at WOT. So now lets only change the gearing (gearing is very important, I think we all agree). So the constants are torque, tire size (265/70R17), transmission ratio (1:1), and speed (60mph).
4.30:1 rear end: 2829 rpms 269hp
4.10: 1 rear end: 2698 rpms 256hp
3.73: 1 rear end: 2454 rpm 233hp
3.55: rear end: 2336 rpms 222hp.
Okay, so same constants.. but this time the torque required changes to 1000 ft/lbs at the wheels. Lets see what that does to hp/tq at the engine.
4.30:1 rear end: 2829 rpms 125hp/232tq
4.10: 1 rear end: 2698 rpms 131hp/243tq
3.73: 1 rear end: 2454 rpm 144hp/268tq
3.55: rear end: 2336 rpms 151hp281tq
So the same work is being done by the 4 setups, but as rpms drop the hp required increases. That's a function of gearing, but the same thing would happen with 4.30's if you slowed down and still required 1000ft/lbs at the wheels. What requirement is increasing? Hp or Tq? Or Both?
They are all putting out the same torque, but the hp changes quite a bit. Why do you think that 4.30s would be rated to tow more? The torque is the same, so all you torque is the only thing that matters people, why??
Bottom line, you cannot argue one over the other. They need each other to be effective. Yes a 300hp 10,000 rpm Honda engine can put the same power to the ground as a 300hp 2,000 rpm diesel.. but getting to 10,000 rpms is painfully slow, lots of gearing (heat) and other issues. Which one will tow better?
To everyone who is comparing personally owned gas and diesel trucks the comparison is very hard to make fair unless both rigs where rated at the same hp, and you operated both at rated rpms. If you weren't, then it's not a fair comparison. The diesel still winds because it makes more per per rpm than a gas engine, thus more power available at average rpms.
I'm a diesel guy, so I think torque is king.. if it's made at the proper rpms. Which means more hp at lower rpms, which means more torque.. Going in circles, but that's how it works. The highest torque in a useable rpms get the work done the quickest, that's explained as horsepower....
