I imagine some of the difference is due to weight (larger engines being in trucks) or performance (sports cars made to accelerate rather than cruise well), but it seems that almost without fail the bigger the engine the less MPG, I don’t understand where the extra energy goes if not to the wheels
In: Engineering
It really just depends on the engine design, vehicle’s gearing, and vehicle weight.
My work truck is a 2023 Chevrolet Silverado with a 5.3L V8. I average roughly 19 mpg in it. One of my peer’s just got a 2023 Ford F150 with a 2.7L V6. He averages roughly 19 mpg in it. Our trucks are fairly comprable. Both four door with 6 ft beds, exact same 10 speed transmission and two speed automatic transfer-case and are both geared similarly on the ring gears. The primary differences, he has a heavier frame, I have heavier duty rear axle, and mine has a mild-steel cab/bed/fenders as opposed to his full aluminum body. The two trucks are with 600 lb of one anther in terms of weight.
Another great comparison, I used to have a 2006 Dodge Ram 2500 MegaCab with a 5.9L Cummins turbo diesel (last fully production year for the common rail). 4 speed automatic and a fixed geometry turbo big, heavy (7600 lb was my day-to-day unloaded weight) pickup. If I could run 65-70 mph unloaded…26 mpg pretty normal. Back it down to 55 mph and I could break 30 mpg with cruise control set (but I live in Texas and no one has time for 55 mph) but if I would bump it up 75 mph I’d see a pretty significant drop to 19 mpg. The way that truck was geared, at 55 mph you just happened to be seeing 1600 rpm (peak torque for a 5.9 Cummins diesel) and at 70 mph I was sitting about 1900 rpm. Break 2000 rpm and the fuel economy quickly began to go downhill and at 75 mph the engine ran at 2100 rpm.
It’s not always a fact of larger engines make worse fuel mileage…but it has a lot to do with engine’s design and the gearing of the vehicle and at which speeds the engine is most efficient.
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