Higher horse power is not a factor for fuel economy

@x1Heavy

To be fair, if you don't need to cross the interstate or even a boulevard, a 4-cylinder bus engine could be considered adequate

 

My last truck had 700 hp and 2250 torque, 18 speed, 3.21 ratio. I used to maxed tridems in BC, total gvw 104,000 lbs. BC is all mountains all the time, and most are real mountains, with mainly 2 lane goat trails with constant curves and grades averaging 6% all the way up to 22%. Yes I could save fuel on the flat by doing 1375 rpms and 72 mph. But I didn't drive for fuel economy, and still averaged 6.2 mpg per month. If my truck was lighter (23,500 lbs tare weight) I could've run down south on the interstates and my educated guess, pulling tandems, would have been 7.8 mpg. Luckily, with my torque, I could have left it top gear and cruise for most of the US, including the rolling bumps in Missouri. Big horse power can save fuel and wear and tear on your motor and tranny.

 

For a minute there I thought Richter was back. First time I was glad I was reading a zombie thread

 

Cummins told me either engine is a good fit for this application. They sent me graphs showing both motors peak at 512 to 513 horsepower and both have 1850 torque. But I like that the E series makes that torque at lower RPM. And it's extended warranty is also cheaper than the performance.
HMMM

x 15 e vs x15 p cummins