I use the engine analogy all the time when people aproach me at the gym about my "weird" stlye of training. I use the engine reference like this.
Say you have an engine (your body). You want to increase power (strength x speed). Strength is (can be) the limiting factor in power. Strength is like the heads of an engine (heads sit on top of the engine block and have exhaust and intake ports). The larger the ports (more strength), the more horsepower you can create. Speed is another compenent of strength. All of the other parts of the engine besides the heads (and of course the size of the cylinders) are the speed.
The most important aspect of power is limiting strength or strength capacity. Once you have a good base of strength (big engine cylinders and head ports) then you add a big intake, a big non restrictive exhaust, larger fuel injectors or carberator, and a supercharger and then you have maximized your strength capacity by adding other things that amplify (strength x speed) power.
If you get bigger engine heads and do nothing else you'll get some good horsepower but it won't be maximized. If you add an intake, exhaust, better fuel system with out the heads, you won't be maximizing power either. You should do both to maximize power.
Think of the pistons as your bones. To much power, torque and snap!
Ok hey, this might not make sense unless you drag race a car, or rebuilt an engine and work on your own body's power output.
Anyone else own a 5.0 mustang?
This post is probably laughable. It's better in person!