FieldEngineer Report post Posted September 30, 2012 Maximum fuel economy is achieved by operating your engine at the RPM where the BSFC, Brake Specific Fuel Consumption, is logged at its lowest. The engine manufacturer has this data. Also, in response to some who said that operating at RPM below torque peak damages the engine; this is only true if the engine will not acclerate smoothly if you step on the pedal. When you take off from a stop, you are operating at less than torque peak RPM and you also know that the engine acclerates without straining. Where operating at below peak torque (lugging) occurs, the engine will not accelerate under load....this is damaging specifically to the connecting rod bearing (upper half). Your auto trans should be set up to prevent this from occuring by downshifting accordingly. Gary Spires Retired Cummins Field Service Engineer Share this post Link to post Share on other sites
andyshane Report post Posted October 1, 2012 Wow. Great topic. I'll pay more attn to the peak torque rpm now, for sure. I've noticed in general, the eastbound drivers are turning in significantly better mileage. Indeed, Caterpillar says in the guide Brett mentions that we can reap a 12% fuel savings from wind alone. Plus, engines vary wildly: my C7 turns in the 7.2 avg of them all, which I can improve upon using the techniques you've been discussing. My buddy with his mammoth Libertyjust returned from a week of camping in Colorado, again beat 8.0 mpg for the trip, despite his heavier weight and 515 hp engine. Similarly, the couple from whom we bought our Fleetwood purchased a Newell and it got better mileage with more hp and a heavier bus. Share this post Link to post Share on other sites
mpoore Report post Posted October 1, 2012 Hello, As a first timer and non mechanical person, I'm open to suggestions. I have a Damon Intruder, 36 ft. Workhorse chassis, 8.1L engine, 345 HP, Allison transmission. I generally leave it in overdrive mode all the time. Is this a good idea or should I shut off the OD when in city traffic. When in OD it shifts into high gear at around 55 MPH and downshifts at around 50 MPH. The longest trip so far (I've only had it for 2 weeks) was around 350 miles in hilly but not mountainous terrain (not loaded and no tow vehicle) and I got 7 mpg exactly. Thanks for any suggestions. Share this post Link to post Share on other sites
