A hypermiling intro...

[GasSavers_rGS]

Originally Posted by SVOboy

For 4wd, I am refering to unlocking the wheels.

Iono why saturns like hot air, but they take to it very well. I, for my part, think cold air results in worse mileage for various reasons.

This is based on what I learned in my Thermodynamics course I took for Engineering.

Basically, the power of an engine is dependent on the overall temperature difference between hot and cold. The cold temperature is based basically on the outside air temperature. The hot temperature is the engine temperature after the combustion of the air and fuel in the cylinder. So power is related to the hot temperature minus the cold temperature.

To illustrate this, let's compare temperature with height. Let's say you're standing on the sidewalk. Let's say the sidewalk represents the cold temperature, whatever it may be. Let's say the top of your head represents the hot temperature. So your overall height is the same as the "temperature difference between hot and cold temperature." Now, imagine standing on a strong box. Now, the top of your head is now higher after standing on the box than before you were standing on the box. Since the top of your head is now higher compared to the sidewalk, that height increase has made you "taller." So thermodynamically, by using warm air intake instead of cold air intake, just like the strong box make you feel "taller", you have given the engine combustion a thermal "boost" in order to reach higher temperatures. So that increases the overall temperature difference which also increases power. Remember, that the cold temperature point is the temperature of the radiator and not the temperature of the air intake. However, it may not be safe to simply raise your engine temperature indefinitely to increase the temperature difference to increase power because even your engine block is made of a material with a melting point like ice cream.

At a relatively more advanced level, I read somewhere that one mod is to replace the thermostat so that the engine runs hotter because the fuel/air mixture is leaner therefore saving fuel. I'm guessing this trick works by tricking the mixture control computer into using less fuel. However, relatively warm air is less dense than cold air. That means cold air has more air molecules per volume than warm air. So using warm air intake, in order to maintain the same fuel/air mixture ratio, the fuel control system would reduce the fuel flow because the warmer air has less air compared to cold air.

I hope this helps.