Designers of different types of internal combustion engines focus on expressions of force and speed that best convey engine power for their own context of use. Race car designers concentrate on producing peak horsepower (hp) at extremely high RPM (revolutions per minute). Diesel truck engine builders tout loadlugging torque (T) produced at low RPM. What complicates the issue of internal combustion engine power is that peak torque and peak horsepower are usually not produced at the same RPM, as with electric motors. This can make a direct comparison of engines confusing.
Things You'll Need
 Calculator or spreadsheet
Calculating the Power of HighTorque Engines

Define the hightorque engine application. For example, the diesel engine in a 40ton cement truck may produce 1,800 footpounds of torque at 1,200 RPM, making it extremely useful for moving the truck up steep inclines. Yet it may produce its peak 480 hp at 2,000 RPM. You can calculate torque and horsepower expressions at both speeds.

Calculate the output torque at 2,000 RPM where maximum horsepower is produced. According to the motor formulas, T = hp x 5,252/RPM. Plugging in the rated values, T = 480 hp x 5,252/2,000 = 1,260 footpounds of torque.

Calculate the horsepower output at 1,200 RPM where maximum torque is produced. According to the motor formulas, hp = T x RPM/5,252. Substituting, hp = 1,800 footpounds x 1,200 RPM/5,252 = 411 hp.

Compare the power output results. At 1,200 RPM, the heavy diesel engine produces 1,800 footpounds of torque to lug the heavy loads, and only 411 hp, while at 2,000 RPM, the engine only produces 1,260 footpounds of torque while delivering 480 hp. For climbing steep inclines, the driver would use lower gears to keep the engine at 1,200 RPM for the best pull, and on the highway would try to keep the engine closer to 2,000 RPM to build speed.
Calculating the Power of HighSpeed Engines

Define the highspeed engine application. A Formula One race car may produce 1,200 hp at 16,000 RPM. Its maximum torque of 490 footpounds at 5,000 RPM is produced in an RPM area that is not even useful to the driver, who shifts gears to keep the engine in its maximum horsepower curve between 10,000 and 16,000 RPM.

Calculate the output torque at 16,000 RPM where the 1,200 hp is produced. T = 1,200 x 5,252/16,000 = 393.9 footpounds.

Calculate the horsepower produced at 5,000 RPM where the 490 footpounds of torque are produced. In this case, hp = 490 footpounds x 5,000 RPM/5,252, which is 466.48 hp, not even close to half of the horsepower rating of this racing engine, where speed is everything.
Tips & Warnings
 Always insist on hightorque diesel engines for lugging heavy loads, and highoutput, highspeed engines for winning the weekend races.
 Always obey speed laws with powerful engines on public roads.
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References
 Photo Credit Concrete truck in the process of pouring a job image by JKeen from Fotolia.com Engineering Trucks image by A74.FR Ben Fontaine from Fotolia.com line of trucks 1 image by Aaron Kohr from Fotolia.com racing car image by Goran Bogicevic from Fotolia.com hot rod engine image by itsallgood from Fotolia.com