A truck engine is a great comparison point, because you can look at modern trucks for a perfect example of this. A Ford F-250 through F-450 pickup truck with t

A truck engine is a great comparison point, because you can look at modern trucks for a perfect example of this. A Ford F-250 through F-450 pickup truck with the 6.7L "Power Stroke" diesel is rated for 475 HP and 1050 lb-ft of torque. The same engine in the same basic truck, but in commercial chassis-cab form, is rated for 330 HP and 825 lb-ft of torque. Step up to the medium duty F-650/750 chassis with a much larger cooling system and that engine is now rated for 270 HP and 700 lb-ft of torque, with optional software upgrades available for 300/725 or 330/750 configurations. The same applies to their gas motor, the pickup trucks get the 7.3L "Godzilla" engine with 430 HP and 475 lb-ft where the chassis-cabs and medium duty trucks get a 335 HP/468 lb-ft tune. The harder and more consistently the truck is expected to be worked the less power the engine is rated for. This isn't just a Ford thing either, GM and Ram also derate their commercial chassis compared to the pickups and the multiple power level thing on the medium duty diesels is common industry practice. Often the highest horsepower packages on larger diesels will be restricted to RV and/or emergency response applications where short bursts of power are more important than the ability to run hard for hours on end.