[Big Dave]

This project has a lot of merit. My truck is fairly similar.

Quick question: Stick or automatic? Just on the face of it a stick is good for a 2 MPG gain. An automatic pretty much forecloses engine-off operation unless you can repair automatics economically.

Tires: Get E-rated tires a size smaller than what you have. I get by just fine on 225-75x16s. I air them up to 100 psi. Lacking any accurately tabulated RR values I default to OEM tires.

Gearing: Very important and huge opportunity for you. Your Cummins (like my IH) has vast low-end torque. You can actually operate at much lower RPMs than you think. I operate at 1325 RPM @ 70 MPH and 1050 RPM @55 RPM and can run as low as 700 RPM around town. I use a double overdrive (ZF6+ GV) and a no-longer-available 3.08 R&P set. By reducing engine RPM at any given road speed you reduce the engine frictional HP proportionately. It is a big deal. At 2000 HP my IH engines frictional power is about 10 HP but it drops by more than 40% at 1300 HP. When you are running at the ragged edge of a "lug" you've got it just right - in the most efficient place on the BSFC-RPM map.

Aerocap: Great idea. There are a number of threads on the ecomodder forums of various options for you. I had a crude aerocap and it was good for a 3 MPG improvement over an open bed and 1.5 MPG over a flat tonneau. Visibility and utility are issues - hence the diversity. Look at aerohead's truck. Its the slickest I've seen. He gets great MPG without any mechanical mods.

Bellypan: Should help but I've never tried it. Same with grille block.

Timing advance: That helps. When it won't start in the winter back it off and that's where you want to be. If you ever want to run propane or CNG back it down to the stock advance. Too much advance + gas fuel = thrown rods.

Engine blanket: Never tried that but I use a 203 degree stat and Evans coolant. If I could find a hotter stat, I'd use it. The Evans doesn't boil (at atmospheric pressure) til over 400 degrees. Hotter coolant makes the engine tighter and more mechanically efficient. Hotter coolant transfers more heat to the atmosphere and your electric fans wouldn't need to run as much. Caution: Hotter stat leads to hotter supply air from your heater and defroster. Mine roasts my fingers on high-dash heat and cracked my windshield in icing conditions where I had to run the defroster real hard.


Please do the ecomodder and pickup truck communities a favor: Don't make your claims based on driving 20 MPH below the posted limit. There is a substantial set of Cummins guys who claim high MPG while driving 40 MPH. That is phoney because nobody drives that way. Determine your MPG over a considerable distance. Any knucklehead can coax high instantaneous MPG on the ScanGuage going slow downhill with a tailwind in perfect weather.

I use a set routine 35% Interstate (70 MPH) 40% state roads (55 MPH) and the rest urban/suburban (running along with traffic) and use a minimum of four fill-ups to to average out the error in determining fill level.

While you are getting other things together, hone whatever hypermiling you feel comfortable with (I'm Sir Coastalot with my stick shift and heavy truck but other than trying to time lights, not much else) and do a rigorous baseline. Then do some mods and run the same routine again.