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john70t john70t is offline
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Join Date: Aug 2001
Location: midwest
Posts: 24,938
Sorry, trying to simplify makes me more confused. If it's remembered correctly:

The gas exchange happens at funky times. The exhaust valve is not just opened when the piston is going up, and the intake valve is not just open when the piston is going down.

It's formulated to the specifics of a constant stream of air in and out of the engine according to the pulsation harmonics of that stream due to the start/stop of that stream.

The exhaust actually opens well before BDC because the work of the expanding air is usless to the piston and the push of exhaust gas out the engine helps suck in the fuel/air charge.

The intake usually opens well before TDC because the suction of exiting gasses helps clear the cylinder of "waste" gasses and pull in the fresh charge.

Except when its designed into the camshaft to keep a little in the cylinder and act as an EGR in economy cars, or (with a lot of camshaft overlap in the case of the dragsters) it loses a lot of the intake charge out the exhaust for the sake of being able to flow air quickly through the engine at high RPMs.

(Sorry if any above info is not correct, please post alternative. Too many bears tonight.)
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Last edited by john70t; 01-30-2004 at 07:51 PM..
Old 01-30-2004, 07:48 PM
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