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Old 05-16-2013, 11:54 AM   #40 (permalink)
t vago
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Originally Posted by jakobnev View Post
The intake, compression and power strokes will happen with a vacuum, but towards the end of the power stroke, when the exhaust valve opens, gas would rush into the empty cylinder. The last upstroke, would then be done with pressure acting on the piston.

Cancelling one up and one down stroke with vacuum, leaves us with one down stroke with vacuum and one up stroke with pressure, netting a significant loss.
I was going to use butterfly valves on the intake side of a V8 engine, in my own cylinder deactivation idea, which is documented here. This was a project supported more by wishful thinking than by thermodynamics analysis, which I could have done even then, but didn't.

However, due to the reason that jakobnev just mentioned, I abandoned this idea. Have you ever tried to pull on a piston to create vacuum? It's pretty frickin' hard to do.
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