Cabover O/O fuel economy question(s)

Probably be close to 4 mpg.
Unfortunately I’ve driven coast to coast with a 300 cummins and a nine speed.
It’ll do it. You won’t be the first one to the top of the hill, kinda a long slow walk.
It’s up to you, that picture shows short wheelbase, I’d figure spring ride, a good air ride trailer will help

 

Pretty close at 4 mpg, if you’re figuring 3k miles a week

 

I’d start by checking the CPL on that engine. If it allows uprate to 350 or 400 that would be my first move. Excepting trains or multi-axle trailers, Formula 400’s used to do 5.7 to 6 pretty easy at Canadian weights if you were half civil with the right hand most pedal.

 

Not sure on the cummins, but I have a 400hp 3406B and 15 speed in my k100, it does between 5 and 6 mpg depending which trailer I have, weight and wind. I did a round MA to FL back to MA with my conestoga couple weeks back, it was right at 5.7mpg. I'd think you'd be winding that cummins out a lot of the time, which will certainly not help your mileage.

 

Go over it with a fine tooth comb. Check alignment, all 3 axles, air filter, change out the differential oil to full synthetic 75w90, ditto on the hub grease, change tranny oil to synthetic 50w drive line oil, get everything as close to spec. as possible, then drive as if there is an egg on the accelerator. You may be able to squeeze 3/4 to 1 mpg extra. As you pull up to the fuel island, thank your luck stars your sled is paid for(hopefully).