Rail Pressure

[mstordahl]

Have any of you found any bennefit to lowering rail pressure in the cruising range to increase mileage? I have heard that added pressure is better for mileage, but was thinking that it takes more power to drive the pump at higher pressure so it might not be that much better. Just a thought, wondering if any of you have tried it either way with good results? Or am I way off base and the old more is better thing correct?

[2007 5.9]

I run lower than stock pressure at almost every condition other than WOT and my MPG isint suffering.

[mstordahl]

Ok, that is what I have been trying as well, no ill effects here for me. Mileage for me has been closely tied to timing, and it is a sensitive balance for sure. Just curious as to if any of you found any bennefit to running the added pressure that overcomes the risks.

Thanks again Les for the quick reply.

[DoghouseDiesel]

Just remember, no matter what you do, it takes X amount of HP to more X amount of weight at a given speed.

Dropping the RP means less fuel is injected. This needs to be compensated with either duration or timing to get the same amount of power.

Lower RP does have the effect of lowering the parasitic loss of turning the pump as hard, but that's not going to make a huge impact on mileage.

Finding the sweet spot with timing as you reduce the injected fuel is where you'll see a mileage improvement.

If the only thing you change is the RP, you'll more than likely see in an increase in your commanded fuel rate, IF you were previously making enough power to move the truck at the speed you wanted.