Quote:
Originally Posted by t vago
Engine tune has a great deal to do with optimal engine speed on the highway. This includes volumetric efficiency of the engine, as considered to be an air pump. If low end on a given engine is questionable to begin with because that engine can't really breathe at low RPMs, then odds are it will get worse FE on the highway with taller gearing, than with lower gearing.
On the other board I sometimes visit, there was at least one example of somebody swapping in a transmission computer to get an extra overdrive gear for their electronically controlled transmission, and they actually ended up hurting their FE as a result. When I looked at the other engine mods this guy had, I could see why.
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+1!
I understand that it's the sum of the whole. I've already made air/fuel/ignition modifications to the motor and thru testing have found more mpg thru smaller injectors, a smaller diameter intake tube (creates higher air velocity thru the maf for increased ignition timing/fuel to offset smaller injectors), and a full time warm air intake by removing the flap valve that directed only cold air into the tube at operating temps.
That and some under-driving of the accessory speeds have gotten me a personal best of 31 mpg so far (it was 26 when all was stock, same as the epa hwy specs). That was at speeds between 65-70 mph constant. Now with the new info, I'm going to attempt the same trip, but 50-55mph speeds and see if I pick up any fuel economy.