What is Valve Shrouding? How & Why does it occur and How can it be prevented?

imagine an open valve, air pours into the cylinder through a sort of cylindrical shape all around the circumference of the head.

Now imagine that valve is recessed like on an old 8v cylinder head and one side sits close to the side of the recess. Air can now only really pour in through one side of the valve because the other is "shrouded" by the side of the recess.

Shrouded valve

This is a shrouded valve. See how the edge of the valve is obscured and hence the flow will be reduced at small valve openings.

I removed some of this material whilst doing a DIY port job on my cyclinder head. There are more photo's in my archive if you have a look.

David Vizard - Porting School #6 - Secrets to reduce valve shrouding

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Originally posted by Rod Ends
David Vizard - Porting School #6 - Secrets to reduce valve shrouding

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