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ICBW, but it makes sense that smaller diameter bearings would reduce drag. It seems like the drag of an oil bearing would be of a fluid-drag sort, and increase disproportionately with the speed of the surfaces, maybe with the cube of the speed?
So a bearing with half the diameter (probably unrealistic, but makes the math easy) and twice the width would have the same area, but less drag. If everything else stayed the same, it seems like it should be (1/2)^3, or 1/8 the fluid drag of the larger bearing. The "Unrealistic Claims" detector just went off, let me go ahead and reset that. It's a big percentage drop, but I figure the drag is very low to begin with, so the actual change would be very small. Apparently windage in the form of the crank and rods hitting oil that's flying around in the crankcase is a much bigger deal. (For airplanes, I know that "spray impingement" is a big factor increasing takeoff distance on a wet runway-the tires kick up water which hits the airframe, making it harder to accelerate.)
There are probably other factors involved, though. It might be that slowing down the relative speed of the surfaces affects the ability of the oil to keep the surfaces from touching, or the smaller crankshaft might not be strong enough, or the smaller bearing might not handle detonation forces, or who knows what else.
I'd suggest roller-bearing mains, but the only engine I ever had with those in it needed oil changes every 1500 miles, which made a mockery of whatever fuel savings it produced.
Would it be worth making a sticky somewhere with things that should theoretically improve engine efficiency, along with the status of each (testing, independent documentation, etc.)?
I.e.,
hotter thermostat, yes,
thinner oil, yes,
HHO, no,
smaller injectors+higher fuel pressure, unknown,
crankcase vacuum, unknown,
thermostatically-controlled oil cooler, unknown,
etc.
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