Engine re-build, eco-style. Home project.

[George Tyler]

On thr rotational mass issue, I have been thinking of adding flywheel mass to make the engine smoother at low RPM when used with my torque converter lockup mod, it is a real limitation at the moment, the engine is very rough below 2000 RPM, I want to be able to run it down to 1000 which would mean I could use 1 gear higher around town.
I have heard of people removing the inside valve spring to reduce friction, if you goind all out for economy you will not be using higher RPM where valve float will happen. the Toyota Prius uses a "Atkinson cycle", where the inlet valves are kept open for much longer than normal so the air that is sucked in on the inlet stroke is partially pushed back out on the compression stroke. this reduces the pumping loss, the vacuum the engine has to suck against. in this way the engine behaves like a smaller engine for inlet conditions but a bigger one for the power stroke, it still uses the full power stroke.

[George Tyler]

the Prius also has narrower main and big end bearings to reduce friction, you could remove some of the bearing white metal from the outside edges. also a dry sump conversion would help.

[Frank Lee]

^Good, forgot about things like that! I know the trend in racing has been to downsize rod bearing diameters, I don't know about mains too but for the rods at least they claim a noticeable friction reduction. I'd think diameter reduction to be more effective than width reduction but of course more expensive to accomplish.

The valve spring idea is good too, if you know it'll not ever get run into the valve float zone. Realistically valve springs return all the energy it took to compress 'em minus internal spring friction and system rotating friction... so the return may be minimal... but if it hurts nothing and costs nothing why not go for it.

I'd go on a campaign to reduce engine driven accessories too.

[bandit86]

I would not downsize bearings, I would run wider bearings with thinner oil. If you need 5w30 stock then go to 0w20 and keep an eye on your oil pressure gauge

[fjasper]

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.