[hotrod]

In order for a fuel molecule to burn it must be both hot enough and have oxygen molecues available at the right time. In a stoichimetric mixture its like you have exactly enough men and women at a party to pair everyone up. If you were to suddenly yell -- everyone choose a partner, by random chance some guys would be able to choose from 3 or 4 girls and some guys would not be near any girls. If there is not enough time to mix some guys and some girls will go unpaired. The closer you get to everyone finding a partner the harder it will be for the last few unattached guys to find the last few unattached girls.

A 12.5 :1 fuel air mixture is sort of like a party where the guys outnumber the girls. If your goal was to be sure every girl found a partner this would be the arraingement you want. When you shout eveyone find a partner (fire the spark plug) it would be easy for every girl to find a compatible guy. Some of the guys would go home single but all the girls would be happy.

Nearly all internal combustion engines make their max power rich at about 12.5:1. This is 12.5 lbs of air to each lb of fuel. This is a rich mixture that intentionally provides more fuel than can be burned by the available air (sort of like the party with too many guys). This ensures that "ALL" the oxygen (or as close as you can get ) is used up as it is the oxygen used in combustion that limits power. You are willing to leave some fuel unburned to ensure all your oxygen is consumed.

The 14.7:1 ratio or ( stoich ) mixture is 14.7 lbs of air to 1 lb of fuel, and provides enough air to burn "all the fuel". If time and condtions allow it.

In a stoichiometric mixture you should have nearly no fuel and no oxygen left after combustion. The problem with that, matching up all the oxygen with all the fuel takes some time. The last few couples take a while to find each other.

Mixtures that lean also burn too hot for most engines to make maximum power with. More of the burning process still continues in the exhaust manifold and as the exhaust passes the valve. This cooks the valve and causes very high EGT's.

Most engines can continue to make more power as you lean them out past 12.5:1 until you get to about 13.2:1 or so, but max power lean is very dangerous and very prone to detonation due to the high combustion temperatures. By running WI you can tune into that 13:1 max power range without melting the engine and without breaking it due to detonation.

This is highly simplified as other issues are involved, but engine temps, detonation and using all the available oxygen are the primary factors in producing maximum power.

Larry