Re: Changing a V8 to a V4

Steve W. wrote:

Forgot to mention - you'd want to have the valves held *closed* not
open. Despite what you'd think, leaving a column of air in a cylinder
is no biggie; it takes work to compress it, yes, but you get it all
back on the downstroke (minus losses, of course.) Pumping losses are
gone forever, however.

nate

And what do you do about the loss of air past the rings creating a vacuum in the cylinder above it?

Nothing at all. When the Chrysler MDS system and the GM DoD systems deactivate cylinders, all they do is keep the valves closed. Yes, there's a tiny leakage past the rings, but it just flat doesn't matter. So what if for 1/16 of the cycle there's negative pressure in the cylinder? Whatever air is in there always acts like a spring and you get >90% of the energy back on the other half of the cycle.
.

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