djcheez

This might be a dumb question but for some reaon i can rationalize both ways so i must ask others opinions.

with overdrive off at lets say 60 mph, rpms 2400, my juice says load on engine is 23%.
while in overdrive, at 60 mph, rpms 1600, juice says load is 35%

which of these scenarios will burn more fuel over an extended period? these speeds/rpms may not be exactly what my truck runs, but i think its close.

just looking at if the "load" reading affects the overall fuel economy? Or am i just to worry about the RPM's?

mitternocht

It depends on the efficiency of the motor at a given RPM and load. My “shooting from the hip” opinion would be the 1600-RPM and 35% load in your example. I’m sure the Cummins engineers could run the numbers for you. 1600-RPM at 90% load might be a different story, however.

wcbcruzer

In overdrive at 1600 rpm is more efficient imo. 1600 rpm is right at peak torque, hence, more torque for the amount of fuel injected into each cylinder = more efficiency.

Although, 0.23 x 2400 = 552 and 0.35 x 1600 = 560. Not sure how accurate the Juice is though..

I don't know if my equation is correct but my reasoning behind it is this... If you were at 100% at both rpms, then obviously you'd burn more fuel turning 2400 rpms constant. If you at 50%, you'd still burn more fuel at 2400 rpm than 1600. So if you multiply the numbers, you can see which yields a higher number (more fuel burned). This is assuming that the "load reading" the juice gives you is directly proportional to how much fuel is injected.

djcheez

when there is more of a load, the egt's rise. this leads me to believe the engine is fueling to keep the speed up. this is of course at the lower rpms. thsi is why i am having a hard time figuring it out.