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Originally Posted by 2.2 Straight six
the reason why the peak torque is always at a lower RPM that the peak bhp (right ?) is because the engine generates the slower "twisting" force going slower that the "hammer-like" swinging/rotating force of the horsepower.
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No.
The reason peak torque is always at a lower RPM than peak, HP is simply because Torque IS horsepower across time. I am not sure why this concept is so difficult to grasp.
You cannot simply say is torque or Hp better. One is a derivitive of the other.
Again. HP = (Torque x RPM) / 5252 (5252 converts the circular movement to time)
Based upon the above.. ALL engines produce the same torque and hp at 5252 RPM. This is simply a mathematical fact since Torque is HP across time.
EG. Two engines.. One produces 200 lbs of torque at 5252 RPM. At that point it is producing 200 HP.
Another produces 210 lbs of torque at 4800 RPM. At that point it is producing only 182 HP. However that same engine might produce 160 lbs of torque at 7500 RPM. At that point it is producing 228 HP.
Got it?
HP is WORK, Torque is force. (typically a circular force)
To convert this into something even simpler.
I have two laborers, pushing blocks of mass across the room. One can only push a 100 lb block and it takes him 20 seconds to move it 100 feet.
The other laborer can move a 200lb block but it takes him 45 seconds to move it 100 feet. The first laborer produces more HP (work). However the 2nd laborer produces more torque (force). In an hour, laborer number one will do more work. (HP)
Now for a selection of laborers.... IF I HAD to move 200 lb blocks. I would choose the 2nd laborer. He, at least can perform that work. If I simply had to move 100 lb blocks, I would choose the 2nd. He would be able to perform more work in a given time.
In the example above the second laborer is a Diesel, or big block low RPM engine. The first laborer is a small 18,000 RPM Indy car.
Given all the above, Torque/HP choice should be based upon the weight of the vehicle and what you plan to do with it. Gearing can be used to get the engines to comparable output torque, but gearing also has drawbacks.
There are lots more to this, but that is about as simple as I can make it.
Jim
SR Racing Inc.