I have figured out a few things that improve an engine's efficiency.
1. proper size inlet and exhaust... Believe it or not the right parts improve milage. Example: 1983 Datsun Maxima 27mpg stock add cone filter and 2.25 inch exhaust and milage was 32mpg. I may be told I'm nuts but I have seen this on many of my vehicles including my current car.
2. proper ignition timing... often vehicles with a distributer ignition are set incorrectly. too much advance will ping and make heat too little will waste fuel by not using it for movement.
3. Compression... again this is old school stuff but more compression means more bang goes to moving the piston. take an 8.3:1 compression OHV 4 cyl and bump that to 10:1 not only will there be more torque available because of the bang getting used better but the burn of the fuel will be more complete.
4. proper brake adjustment... often this is something people overlook and a dragging brake will cost lots of MPGs.
I am no expert I don't claim to be one but I like to share my experience if it will help
engines 101... no offense but why does there need to be another thread about the absolute basics?
1991 Toyota Pickup 22R-E 2.4 I4/5 speed
1990 Toyota Cressida 7M-GE 3.0 I6/5-speed manual
mechanic, carpenter, stagehand, rigger, and know-it-all smartass
"You don't get to judge me for how I fix what you break"