Ideal cruising RPM for MP8?

You are beating the engine up hard and are correct that 1300-1350 is ideal on that rating for cruise rpm. (1700 is out of the power band on those motors, they are happiest at 1100-1600)

Fuel economy will definitely increase and the engine will last much longer.

You most likely need to be in the 3.08 range. I would bet a steak dinner you pick up about 1.5 mpg or better with 3.08s ... the Mack motors hate rpm and get very thirsty up there

 

I dunno why RPM terrifies truckers so much. Its like they think its gonna come apart if it ever hits 1800 lol.

 

With 3.23 rears you could run 78MPH at 1450 RPM.

 

The sweet spot in torque is a balance between the final gear ratio and the camshaft.

 

You need to change the ratio to 3.08, with the 18, you can use the lower gears without any issues at 65k

 

I know i think it's funny as hell. The schlumberger trucks were ran wide open 1900 rpm at 65 isx. The fuel mileage will suffer a bit but your not constantly pounding the #### out of it at max tq all day. Trust me that motor will last longer running higher rpms than lugging it all the time. A rebuild will cost way more than a little extra fuel

 

I've driven all these newer motors except the paccar and below 1300 they all fall flat on their face