RE: improve mileage
Run good fuel, keep filters clean, always operate with adequate power.. explanation:
As counter intuitive as it sounds, don't fear the rpm.. don't bury it either though.. engines are more efficient in the completeness of the burn of fuel when they aren't struggling to produce power.. a lot of folks believe that higher rpms means more fuel used, and oil burner make a better case with that argument than gassers, but this principle holds true for both, and here is the counter intuitive part- when youre driving along in a gear ratio that is lower (numerically higher) the engine doesn't have to work near as hard to get and keep the load moving.. if youre in a higher gear, and the engine is struggling to maintain the speed, you're gobbling fuel..
On the open road unloaded, fifth locked rocks.. specific to these trucks, its the best of both worlds, as the engine produces plenty of torque around 1500rpm to keep you moving around 50~60mph.. in that same gear, pulling say 10k#, the engine has to work harder.. its evident in terms of egt and boost.. if you were to drop to fourth locked, the engine rpms will increase, but it will also stop struggling- as in, its cleanly burning what fuel its injecting.. in those conditions, you're actually burning less fuel..
I'm typing from a mobile, and I'm about to type a lot.. sorry fellas, I'm bored..
Gears vs Rpms
It's a mathematical certainty.. if you're turning the shaft x number of times, and your overall drive ratio is known, you can give exact speed... Take any of those two factors and you can determine the other.. its a fact that can't be altered, unless something Is wrong such as trans slipping or tires losing traction..
Boost vs non boost
If you are pumping 14psi into your engine, you've added an entire atmosphere.. your 6.4l displaced engine is now actually displacing the equiv of a 12.8l engine.. yah, there is always the case of dynamic compression and displacement as compared to mechanical displacement, and the volume differences between the two (if the exhaust doesn't close until 4* above bdc, you're not actually displacing that cylinders full displacement, but instead its full displacement minus the volume the 4* represents: whallah, dynamic displacement).. to maintain proper ratio, guess what your engine needs when boosting an additional atmosphere? More fuel.. or, close to twice the fuel needed for zero boost.. gulp gulp..
Making them jive
Boost is fantastic to get a load rolling in short order, and has a sweet ability to launch under one ( or three!!) Atmospheres with these rigs, its REAL benefit is evident when you're rolling along at cruising speed, and it withdraws adding pressure.. think of your turbo engine as having a monster under the hood with all the power you need to move a load, but with the curious ability to shrink in displacement as it Is needed.. imagine that engine effortlessly achieving speed (gears+rpm), but then being able to find a sweet spot using those gears and rpms to be able to reduce or eliminate boost, and still not struggle to maintain velocity..
See where I'm going with this?
If you wanna dial in economy, you gotta find a gear selection that allows you to maintain the speed youve selected (regardless of tow/haul+ truck weight) with as little boost as possible, and with a steady but relative to what you're doing low exhaust temperature.. let the truck increase boost as needed for altering drive conditions, but if you see it really climbing, pop your gears lower to compensate instead of pouring fuel at the engine.. an automatic transmission is supposed to do this for you, but you can dial it precise and add economy by using the lever, or the button on the end of it more often.
Caveat: these diesels produce gobs of torque down low and throughout the rpm range.. since they do just that, higher gears can be used and maintain velocity without the weight stripping it away as it would In a gasser.. meaning, it is easier to 'plane' off with these things..
Clift notes: its mostly driving style that will determine economy.. and this is important more than anythong else I've said: let the truck and the load determine your speed instead of what some sign tells you is legal.. you may find yourself putting along sometimes, but others you'll find yourself looking rapidly over both shoulders for cops while youre sipping slowly on the gogo juice..
As an aside, I just finished tank three on this truck that is new to me.. hand calculated, I'm getting 18.3 miles per gallon combined driving.. once I'm done playing with my new toy and leave hammering the throttle behind me, I fully expect to see slightly over twenty.. man, its nice living at sea level and on flat terrain.. that o2 burns more powerfully and the truck never leaves 5th locked once I get her to speed.. that alone accounted for three to four mpgs in my last gasser.. I expect its similar to that, but maybe a little less with the oil burner..
Last edited by drewactual; 11-20-2012 at 08:35 PM.