a technical discussion, engine efficiency Options

[r_towle]

so, I have been thinking (not always a good thing)
If an engine is basically an air pump, and the objective is to make it as close to 100 percent efficient, why is the exhaust valve so much smaller than the intake valve?

Forget emmisions, forget fuel delivery, just want to understand why this is so...it is so on most engines...

Rich

[lapuwali]

IMHO, Brett didn't "nail" anything. Both of you are just being pedantic.

Yes, airflow will always move from a higher pressure to a lower pressure. Reducing the pressure in the cylinder below the pressure of the air in the atmosphere will induce flow from the outside, through the intake tract, into the cylinder.

In common use, "vacuum" is simply "pressure lower than atmospheric". The fact that pressure pushes rather than vacuum sucking is simply idle semantics, and makes zero difference to the actual operation of the engine. You may as well go around constantly correcting everyone who misuses the terms "torque" or "force" or "work".

Describing things in "layman's terms" is USEFUL, and was exactly what was asked for by the original poster. Indeed, if you can't sufficiently explain something in non-technical terms, either you don't really understand it, or you're an inarticulate Neaderthal (hey, would you like to beat me up on the them "Neaderthal" now?).

Neither one of you have actually added to the conversation. Brett's statement: "The NASCAR boys have done quite a bit of testing to deterimine valve sizes and such. They have been increasing the intake size and skrinking the exhaust until they can run the smallest exhaust valves possible." My response would be: fine, WHY? Things are the way they are because the NASCAR boys say so? What's the theory behind this?