Originally Posted by ap72
The argument is essentially you can have an engine with less torque and go faster if you still put more average power to the ground in equally prepped cars. And yes, you can have more torque and win, BUT it is not needed. Which goes to show, average HP put to the ground is all that matters- not torque.
Secondly acerage is not as important as dimensions, for reasons you stated.
I've really been trying to stay out of this but I'll stick a couple toes in.
Horsepower is a measure of work, torque is a measure of a particular kind of force (a force wanting to cause a rotation but not necessarily doing so).
Work is the result of a force resulting in a movement for a distance in a period of time. I once used the analogy a few weeks ago in this forum that if you used a lever against a heavy object that if the object couldn't be moved by the force applied that no work, therefore, no horsepower occurred no matter how much you sweated in the attempt.
I use a "lever" because it is a length suspended at some point by a fulcrum, therefore its movement is rotational, therefore, the forces in and out are torques.
The gasoline fueled engine has two points hot rodders worry about they are the torque peak and the horsepower peak. The torque is there from the moment the engine is started till it's wound up where it throws its rods. The horsepower is also there as simply stated as Torque times RPM. So an engine that turns slowly but makes big torque numbers can also make big horsepower numbers at those low RPMs. Engines that propel big ships come to mind. An engine that turns very fast but makes small amounts of torque can also make big amounts of horsepower at high RPMs. A Formula 1 engine comes to mind. But neither of these engines would be suitable powerplants in your F150. So this brings us to a conclusion that an engine has to be a size in proportion to its assigned task.
Back to "peaks"! The torque peak is nothing more than that place where the engine is taking the biggest breath it can. On a dyno an engine is typically accelerated at a rate of 300 RPM per second. The force it takes to limit the engine to this rate of acceleration is read as torque and computed to horsepower by Torque times RPM. OK, the actual formula has some stuff I'm leaving out to which there is a whole nuther story as to why 33,000 pounds per second and 5250 RPMs are used. But lets just stay simple for a while with Torque times RPM. RPM is a distance in time in one little statement. The torque is a force across a distance together they make "horsepower".
I keep getting in these side things, back to torque peaks. The torque is there below and above the peak, it can be tuned into horsepower thru the formula at any time. The torque and horsepwoer is variable with the amount and frequency each cylinder can contribute to the crankshaft. At RPMs under the peak the frequency are lower and the operating pressures are lower because the engine isn't yet spinning at a point where all the Beach Boy vibrations have become Good Vibrations in the intake and exhaust systems. So at the torque peak the engine is breathing as deeply as it ever will and the torque hits its max value. Past that point, there becomes insufficient time for the induction system to get mixture in and the exhaust system to get the poop out. So the absolute pressure in the cylinder begins to fall and the torque per revolution begins to fall. But back to the equation that Horsepower which is work accomplished keeps going up because the RPMs are raising faster than the torque is falling. This continues to the horsepower peak.
The horsepower peak is simply that point where the increasing RPMs cannot offset the falling torque. At that point the horsepower peaks and begins to fall. How quickly it falls will mostly depend on the carburation/injections ability to feed the engine, camshaft design, compression ratio and the efficiencies of the intake and exhaust systems. Some engines come up to the horsepower peak and just flop over in a dive to zero, others will flatten out for a while before they too flop into a power dive.
In a drag race, you want to operate the engine in an RPM range where it has its best acceleration. Typically that is the zone between the torque and horsepower peaks. This was the point of the close ratio transmission, it was intended to keep the engine within the range on shifts. The wide ratio was more suited for the street with a deep low and a wider spread till you got to high. But this forces you to operate the engine in a range that usually requires the engine to be over revved to come back on the torque peak with the upshift. Or you can shift on the power peak and bring the engine under the torque peak on the up shift. The dynamics of the engine, the trans gearing and those of the chassis will determine which choices result in the least time to the finish line. Obviously the perfect solution, short of an electric motor, would be an infinitely variable transmission that held the engine on the horsepower peak all the time as it changed ratios. But in spite of this being and engineer's wer dream for a hundred years, the technology involved still exceeds the material strengths and process controls we have, but that gap is closing at least to the point where underpowered cars like the Subaru Justy could commercially play with the idea.