Fuel Mileage
 

And the driver probably has a Detroit or Mercedes for power and you know how good on fuel they are.

Re: Fuel Mileage
 

2004 International 9400 with a wind deflector on the roof .. pulling 53" dry van. I have a 475 hp CAT with 1,650 lb/ft torque, 13 speed tranny with 0.73 top gear ratio, and 3.73 rears. I recently switched to low profile tires and I dropped a mile on the speedometer at the same RPM. I get decent fuel mileage (between 6 and 7 mpg) even fully loaded but only because I stay within the engine recommended RPMs. For my CAT, it's 1,300 to 1,400 RPM. I usually do 58 mph with a light load (1,300 rpm) and 60 mph with heavy load in hilly terrain (1,350 rpm).

1,800 rpm sounds too high even for a Mack engine... I'd suggest you found out your engine best RPM range, and maintain the road speed that puts you in that RPMs. You might need to get creative with axle ratios, tires (tall rubber will help you drive faster at better MPG), tranny top gear ratio, etc. But driving outside of your engine favorite "spot" is a sure way to waste tons of dough on diesel.

Fuel milage
 

'03 379 Pete, 475/500 Cat, 18 speed, 355 rrs, flatbed. Coast to coast operation. 6.212 mpg since new. Down to 6.1 since low sulpher.

There's so many variables.

Driveline specs are about 20% of the factor.

A more efficient engine doesn't matter if the driver is doing 75 mph.

It's the total package:

- An aerodynamic truck AND trailer
- Low rolling resistance tires(super singles or XDA energy)
- Driven at less then 60 mph
- Eliminate idling
- With good specs for 60 mph(2.64's or 3.55's)

Will net you 7.5-8.5 mpg. That's not a joke.

quote="allan5oh"]There's so many variables.

Driveline specs are about 20% of the factor.

A more efficient engine doesn't matter if the driver is doing 75 mph.

It's the total package:

- An aerodynamic truck AND trailer
- Low rolling resistance tires(super singles or XDA energy)
- Driven at less then 60 mph


*road speed is much less a factor than the resulting engine speed*

- Eliminate idling
- With good specs for 60 mph(2.64's or 3.55's)

Will net you 7.5-8.5 mpg. That's not a joke.[/quote]

Are you saying that specs matter more then road speed?

I'd rather have an engine revving 100-200 rpm too high at 60 mph then spot on at 70.

Cummins fuel mileage paper states 4% difference from a perfect spec to a bad one.

Road speed makes many times more difference then that.

If you want to do a test, take a truck with instant read out.

At 60, shift down 2 gears if you have a 13 speed. Notice the difference.

Now speed up to 70 in 13th.

I absolutely guarantee you at 70 you will get much worse fuel mileage.

'As the truck speeds up from 60 to 70 mph', what causes the fuel efficiency to decrease?

I don't believe in the accuracy of your instant readout.