Quote:
Originally Posted by abogart
My understanding is that the engine is going to try to fill the cylinders up to whatever the displacement is. Whether air is restricted by the valves (cams), throttle, or intake piping, anything that restricts that air is going to be... Well, a restriction. And I always thought that anything that restricted exhaust lowered output and, therefore, efficiency as well. Apparently my thinking is flawed if some are seeing better numbers by actually adding restrictions.
Would anybody care to elaborate a little further on intake and exhaust tuning?
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a LOT of this is theory, with suspect application in in the real world.
The intake is as you describe - a restriction is a restriction, and the throttle plate works as good as anything else, so changing the intake for added MPG is probably not going to work.
On the exhaust, for mpg, the argument is you want to keep some exhaust gasses inside the engine for better mpg. the argument is there are pumping losses for a gasoline engine, and the exhaust gasses "fill the chamber" which is more efficient then a vacuum.
Variable cam timing does the same thing - at low speed keep the exhaust valve closed longer to get all the power out of the gasses and keep some of the gasses inside the cylinder.
These are subtle gains, but perhaps they can add some MPG.