Not a car, A truck Fuel question

Cherry

DREAD NAUGHT
Joined
Mar 24, 2008
Messages
416
Location
western . AZ
Seeing I have a 1999 Frieghtliner FRD120, Its HP setting is 430 HP normal, 470 HP cruse control on.

Normal pulling 80000 lbs it gets 6.5 MPG

Question: If I cut the HP back to 350 HP, pulling 19000 would I get better MPG?
 
I will say yes,on a diesel engine HP can be regulated by turning the fuel pump up or down,now on a computer controlled engine i would think it still applies,the older Dodge trucks with the Cummin's motor still had an external fuel pump,you could really turn those baby's up,the tranny and rear end did not like it though,and it is the same with my tractors i can turn the pump up on them and make more HP and TQ only down side is the fuel economy goes to crap. I have never turned one down so i am not sure how much of a fuel savings is there,just turned them up :D
 
Seeing I have a 1999 Frieghtliner FRD120, Its HP setting is 430 HP normal, 470 HP cruse control on.

Normal pulling 80000 lbs it gets 6.5 MPG

Question: If I cut the HP back to 350 HP, pulling 19000 would I get better MPG?

I have an F-350 Ford diesel dually crew cab and notice a big difference in mileage over and under 1800-2000 rpm....
 
Fuel mileage is a funny thing on the OTR diesels. They went to the dual HP rating for fuel mileage. It gets better mileage with the cruise on at 470 HP than it does on the foot at 430 HP. It doesn't have to work as hard at 470 as it does at 430. Will it help for your application? No idea. But that's the reasoning behind why they did it.
 
Seeing I have a 1999 Frieghtliner FRD120, Its HP setting is 430 HP normal, 470 HP cruse control on.

Normal pulling 80000 lbs it gets 6.5 MPG

Question: If I cut the HP back to 350 HP, pulling 19000 would I get better MPG?

Youll get better MPG because of the weight. 6.5 pulling 80000lbs gross needs more power than pulling 19000lbs.

The one thing that helps the MPG is the ratio of gearing and speed traveled.

you have to get the engine to operate where the engine burns less fuel to operate.

Lets say your engine is more fuel efficient at 1300rpm and you cruise all day at 65 mph. then you have to select a ratio that will keep the engine at that RPM for that speed.


I have a Peterbilt with a Cummins 550 hp rated at 1800 lbs of torque. 13 spds.
Ratios on the diffs are 3.70.

my engine is more efficient at between 1250 and 1350 rpm so I try to cruise around that range witch bring the speed at around 60 mph and get around 6.5 mpg
If I run it at 65 mph the mpg will drop to 6 mpg.

Slow down and cut the idle time that helps a lot.
 
Top