On Thu, 5 Jun 1997 18:00:45 -0800 gbaker@customcpu.com (Baker, G.)
writes:
>At 01:14 PM 6/5/97 -0700, you wrote:
>>Hi Jay!!
>>
>>On Tue, 3 Jun 1997, Michael Hartwig wrote:
>>
SNIP
> While I'm here....someone explain what "shrouding" is. I think
>it's inherent
>in the head design and "bad" but I really couldn't get a good feel for
>what
>it is.
SNIP
Shrouding, when talking about automotive valves, simply refers to the
proximity of the cumbustion chamber wall to the valve.
Without getting into a bunch of math and theory, shrouding occurs when
the distance between the edge of the valve and the chamber wall is too
narrow to allow full flow of intake (0r exhaust) gases through that
section of the valve opening. To use some hypothetical data, assume you
have an engine with a 1" intake valve, and the cam/rocker combination
allows .33" of lift at the valve face. Also assume the for a distance of
.25" the chamber wall is only .10" from the valve edge. The nominal valve
opening area would be Pi time the diameter times lift or about 1.04 sq.
in. But, that section (.25") has only a real opening of less than .03 sq
in., instead of a total opening of about .30 sq in. So the total
availible opening is now down to about .83 sq in. for a loss of nearly
20%
The technicals are somewhat more complicated, when port direction,
charge inertia, lift rates, etc,etc. are factored in, but the basics are
pretty much the same.
By the way, in Vizards book, he covers valve shrouding both in theory and
in practice (for the A engine). The theory is aplicable to any engine.
just my tuppence worth, hope it helps
Rick Morrison
72 MGBGT
74 Midget
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