Mar 16, 2012 · PACCAR MX-13. The Strong, Silent type. Common rail system maintains injection pressures of 2,500 bar so the engine is exceptionally quiet and efficient. Horsepower ratings from 405 hp. to 510 hp. with torque ratings of 1,450 lb./ft. to 1,850 lb./ft. Availability in both straight torque and multi-torque configurations. The PX-7 is a dinky little thing, with eleven variations ranging from 200 horsepower to 360 horsepower, and peak torque ratings from 520 to 800 pound-feet. The most powerful version of the PX-7 is weaker than the weakest variation of MX-13, and PACCAR themselves suggest the PX-7 for use with medium-duty vehicles only.