VTEC (not really), and DOHC

[fiberglasscivic]

I really would like an explanation of the difference as well but until then I'm going to answer this question with a little less of a technical explanation.

If the valves were opened more, why would that affect the fuel/air mixture?......... If the fuel/air mixture was more rich, how would it choke the engine? Especially since the bigger openings allow less restrictions on the intake and exhaust strokes.

From this quote I'm going to assume that you don't understand the meaning of rich and lean and that would explain why you don't understand how you can choke the engine. If you open the inlets wider and allow more gas and air than the engine is going to be able to use then you will end up exspelling fuel into your exaust (thus wasted fuel). There is such a thing as too much fuel. You can reach a point that there is so much fuel and not enough air in the chamber that you won't create an explosion. This is how you can "choke your engine" (also know as flooding). By controlling the amount of fuel and air that is allowed into the chamber and at what RMPs, you can create a balance that will allow you efficently use your fuel.

The technical aspect of this comes when you take into account that your engine has to use some of the power created by the explosion to expell what is left in the chamber. The more fuel that you put in the chamber and don't use is hp lost because you have more to expell. This is also why changing the diameter of your exaust pipes can increase HP. The less resistance to pushing the expended fuel and air out of the chamber, the less power required to move it. The less power you use to exspell your exaust, the more power that goes to your wheels (or the many other aspects of your engine that require part of that power).

Rich means that the engine is recieving more fuel than can be used while lean is just the opposite (not enough fuel).