Proper thermostat - this is crucial. If you are running too cold (160 carb, 180 TBI) then your engine never reaches proper operating temps. This means significantly worse efficiency and bad MPG. It's like driving with your choke on all the time. It also causes breakdown in the oil and other issues that cause premature engine wear.
More.
Actually heat=power. A 195* is what GM spec'd. It's as much for emissions as it is performance AND engine wear. Metals expand and contract based on heat, tolerances are factored considering "growth". Obviously you can't go ridiculous like 300* engine temps, but increased cylinder temperature equals more power. (think about what makes premium required in a high compression engine)
A good example is aluminum heads. Due to their heat sink characteristics, typically more timing and compression is required to produce as much power as iron heads, all else being equal. Plenty of testing to back that up.
Intake that draws cooler air from outside of the engine bay (usually via the snorkel tube). Cold air is more dense than warm air. Therefore, cold air holds more oxygen and hot air holds less oxygen. Oxygen is what burns. If you want better performance, get more oxygen into the engine (like a turbocharger) that is cooler.
Making sure the intake tract (intake, air cleaner, filter, throttle body/carb, etc) isn't a restriction is what increases MPG. Hot air keeps the atomized fuel from falling out of suspension on a wet intake system such as TBI and carbs.
If you increase the volume of air entering the engine, you must also proportionally increase the volume of fuel added to the intake charge. That's what lean is. A computer will adjust to this for you, on a carb you need to have your jetting right. Net increase in efficiency from cooler intake charge has to be zero.
Super and turbo chargers (and to a lesser extent cold air intake) make more power because they increase the amount of air/fuel the cylinder is filled with. It doesn't change the ratio of air/fuel required, except when you start getting into volumetric efficiency, efficiency of the forced induction, and so on. You may be doubling (WAG) the amount of air/fuel put into the chamber, but that is why fueling them is so critical...the super/turbocharger adds more air, without adding the extra fuel, you burn the motor up.
Good spark plug wires. Restrictive wires mean less power.
Good coil. Is your coil giving 50% power? You are losing efficiency.
There are plenty of test out there that showed under normal (what I'll consider non-racing) conditions, an old HEI unit, with old stock-type wires, made just as much power as a new MSD setup. I believe that particular test was in a four wheeler magazine as a matter of fact. The simple fact is, ignition needs to be in good condition, which is what you are getting at. HEI however, is extremely forgiving. No excuse to have a bad plug, wire, or corroded cap/rotor terminals.
Stock exhaust manifolds are typically very restrictive. If you can get equal length headers (to maintain proper backpressure and exhaust scavenging) that can help tremendously.
Backpressure is bad. Backpressure is NEVER desirable. Backpressure prevents scavenging. backpressure and scavenging are two separate animals. If you have exhaust backpressure, engine vacuum increases, same as if you had too small of a carb. The engine has to work harder to expel the exhaust out of the cylinder. Scavenging is essentially suction through a tube....you can't have suction if there is pressure the other direction.
As a matter of point, one GM test for clogged exhaust is to tap into the exhaust system before the converter and measure pressure at WOT. If anything over 2-3PSI, there is a problem.
Another test is to measure intake vacuum at WOT. If intake vacuum increases, you have a restriction somewhere.
I hope you don't take this as a direct attack. It's not intended that way. This thread is about economy, there is a ton to consider about it, since much is related to engine efficiency.
