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Originally Posted by wstrohm
Question regarding emissions:
How much fuel vapor actually escapes out the airbox intake when the engine is shut off? With port injection, all the entire intake system up to the ports contains only air. When the engine is shut off, where is the pressure difference that would flow air + fuel vapors back out through the intake manifold, piping, and airbox? And wouldn't the stock (paper) filter trap most of that?
My intuition says the charcoal filter in the intake system is another politically-correct step taken by a government bureau regardless of the true benefits and the cost to the manufacturer/consumer. Hard to see how any real amount of vapors would escape totally; more likely they would just sit in the intake tubing and upper section of the airbox until the next time the engine fired up, when they would get sucked into the engine along with the intake air.
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Maybe with the valvetronic system and the absence of a throttle butterfly, there is more chance for gas vapours to come up thru the open valves.
