no1tovote4 said:
On investigation it appears that the engine would use the same amount fuel but have more power because more of the fuel is burned thus giving the effect of having a larger valves without incresing the size of the engine. This means that you would have more power thus a higher energy efficiency, but not save fuel by its use....
That's not the case in practice, however. Because a supercharger (or any forced induction method, to include N2O) adds oxygen to the engine's intake supply, additional fuel must be added as well. This can be done, and MOST off-the-shelf superchargers use this method, by increasing the fuel injector's fuel pressure. The injectors open and close at the same rates they would normally operate at, but due to increased pressure behind the little 'valve' within each injector, MORE fuel is injected into the intake manifold (usually - there are very few direct-injection engines where fuel is sent DIRECTLY into the combustion chamber).
When an engine gets too much oxygen, and not enough fuel, it's considered to be running 'lean'. Lean is GOOD for making power, but lean conditions can create VERY high temperatures which can lead to the air/fuel detonation BEFORE it reaches the combustion chamber - this can produce VIOLENT stresses upon engine components (If an exploding force is trying to push a piston DOWN when the crank is moving the piston UP, for example).
Thus - added fuel, via increased fuel pressure effectively cools things down at the cost of a power which would otherwise be there. A good supercharger system contains the components for effectively protecting the engine AND increasing engine power.
Why I said a supercharger 'could' improve economy I was meaning one can use a little less RPM to get the power they otherwise would have had to rev the engine higher to get.
As an example, if I need my car to get to 100lbs-ft of torque (for whatever reason) without a supercharger, I'd have to rev my car's engine to, say, 4000 rpms. WITH a supercharger, I may only have to rev the engine to, say, 2000 rpms to make that same 100lbs-ft. I'm of the opinion RPMs, NOT throttle position are the key to achieving good economy with a given engine.
[edit]
side note - I hope I'm not insulting you, D. I made my post w/o knowing how much you already know about Forced Induction.
