[Floordford]

What can be done to a good running engine to make it more efficient? By that I mean it already would have good plugs, coils, new oil, new air filter, etc. basically in great running order.

My thoughts go to polishing the intake and exhaust ports on the head so that the engine strains less. Possibly a slightly bigger exhaust system. Or more powerful coils for better combustion. A custom grind cam, but it would be very much blind guessing. Higher compression for more power with less throttle. Lighter rotating assembly like a lightweight flywheel, crankshaft, valves, cam gears, rockers, spring retainers.

I also wonder what makes for a more fuel efficient engine as means to more horsepower or more torque. By that I mean, some cars have long intake runners to make more torque. Other cars have short intake runners to make more horsepower. No doubt this would need to get matched with things like cylinder volume, bore, and stroke. But one or the other might fetch better efficiency.

Most of my ideas come from making an engine more powerful to race but it stands to reason that if an engine doesnt have to strain as hard to make power then it should get better MPGs. So long as those mods dont cause it to use more fuel.