Downsize HP's

Yeah, i have to agree with Bman on that, but from my personal experience, if you turn that truck down too far, you will lose fuel mileage. I drove a columbia with a 515 det in it, and it was great, lots of power and torque, and still got 6-7 mpg (depending on how hard you pushed it and how much we idled). Then drove another columbia with the same motor (turned down to 65 mph and 430 hp) and that dog would only get 7 mpg when REALLY light (10-15k).

 

When you have a truck turned down, you are in essence "choking it" and loss of fuel mileage is common. This is why most 65-68 mph company trucks get crappy mileage.

 

Ok let me answer this with a real life situation over 1,000,000 miles of research. I had a Freightliner FLD 120 70 inch condo with Detroit Series 60 13 speed over. it came from the factory set at 430 straight 1500 ft lbs of torque and 1800 RPM. I drove it like that for 100,000 miles till it was broke in average 5.5 to 5.8 MPG. I had it turned up to 430/470 1850 ft lbs torque and 2100 rpm. Now i drove it the rest of its time over 1,000,000 miles plus before i sold it. When we pulled the figures out of the computer when i sold it. It averaged 6.8 mile to the gallon over the miles driven. I actually got between 6.0 and 6.5 most of the time i drove it not counting the occasional 5.0 or 7.0 loads that would be normal for real heavy head loads with heavy head winds and real light loads with tail winds. I found it pulled better and ran better as long as you drove it right and stayed out of the top end all the time shifted around 1650 to 1750 and kept the cruise control on and the extra was there i just never needed it unless i was in the hills and then it was nice to have the extra when you needed it. just like it would run over 100 MPH but why. It just gos back to just because you have it doesn't mean you needed it all the time. It all in the driver. I had friends that had cut back trucks with all kinds of limits on them and they got worse millage then mine did. It's really all about finding the sweet spot on your motor. the Detroit was 1500 it loved to cruise right there and would pull the guts out but it was about 60 miles an hour the way my truck was geared so if i had changed the gears in it for out west it would have been a whole lot better on fuel. but with 3.79's it did go up hill real good.

 

Its true. The more load on the motor the worse the milage. The huge HP black smoke billowing Cat may be getting more MPG than you think.....
If you can keep your foot out of the throttle when you don't need to be in it you will get pretty good mileage. A turned down truck, you have to stay on the throttle to keep your momentum up. So you are burning more fuel to get less HP.

 

Think of it like an old horse and wagon setup, a six horse team might not pull it any faster than a four horse team but six horse won't have to pull as hard. If your rear end is geared so your sitting near of your torque peak at your driving speed you'll get your best mileage and a large torque reserve (horsepower is torque applied over time) means the engine is working less further improving fuel use figures. More horsepower properly applied is a GOOD thing.

 

AND don't SIT to close to the SADDLE HORN!