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Dodge Ram Diesel FAQ's
Horsepower And Torque

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Q: What  HP ratings are available from factory for the 12V Cummins B?

Q: What  HP ratings are available from factory for the 24V Cummins ISB?

Torque = strength of a rotation or twist expressed as force times distance. The torque rating of an engine ultimately determines how heavy of a load the engine can move

Horsepower =  the rate at which work is being done = RPM x Torque / 5252.  HP determines the rate at which a given a load can be moved.

POWER, TORQUE, & HORSEPOWER Explained - from the Diesel Injection Service page
POWER, TORQUE, & HORSEPOWER Explained - from the Site
POWER, TORQUE, & HORSEPOWER Explained - from the How Stuff works site

Q: Why does the diesel produce so much low RPM torque compared to a gasoline engine?

Diesel engines have a mechanical advantage over the gasoline counterparts because:

Q: The pickup diesels produce 400+ ft-lb of torque and only 230 hp. Some small automotive gasoline engines produce less than 200 ft-lb of torque, but more than 230 hp. How can this be?

Horsepower is calculated using this formula: HP=RPM x Torque / 5252. A small gasoline engine  may have a torque peak of only 230 ft-lb, but the engine hp peak occurs at a redline of 6500 rpm with an ouput torque of 195 ft-lb. HP = 6500*195/5252 = 241 hp. 230 ft-lb would require very low gearing to move a heavy load, but it is easily capable of moving a small, light automobile.

Q: OK, so how about using a small gas engine with a turbochanger and a lot of gears?

The diesel is best suited for heavy sustained loads for long hours. While a small vehicle seldom needs high engine power for more than 60 seconds, a large loaded truck moving at highway speeds often requires long periods of sustained high engine power. The gas engine running at full throttle and turning 6500 rpm will not live for very long. Remember that race engines, which run at high rpm and full throttle, are built with special high-strength components and may see 500 miles in a four hour race - then they are rebuilt. Street gasoline engines can survive, at most, for about 200 hours at full throttle before they go bang! Slower, heavier diesel engines can usually run for 5000 hours at rated power before and overhaul is needed.



Last update May 3, 2001