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Discussion Starter · #1 · (Edited)
I've got a set of small block heads with 1.94" intake valves. I'd like to upgrade to 2.02" valves, but am concerned about shrouding and possibly losing flow.

Question:

How much clearance do you need between the wall of the combustion chamber and the seat /and/or/ valve so that you eliminate/limit the effects of valve shrouding?

I had heard that GM used a 2.34" cutter centered in the intake valve guide to remove the material that would shroud the valve. Is this true?

Best Regards,

Mike
 

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I think GM plunge cut them so that they have about a 3/16" chamfer/radius on both valves walls down at the bottom...

pdq67
The only cut GM did was around the intake, not the exhaust. I have a photo of an L79 head I can post later tonight. How they did the cut I can't say but when you see the photo of the cut maybe you can make some inferences as to how it was done.

I'm not sure what size engine you are building, but I wouldn't try using 2.02 valves on anything less than a 4-inch bore.
 

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The valve seat area is cut pretty widely on the exhaust side to accommodate the slightly larger valve, so maybe that's what looked like a relief cut. And like I said above, this is a cast-in-1964 L79 head, maybe it was done differently on other 2.02 heads.

To be clear, there is NO difference in the casting (461, 462) used for 1.94 and 2.02 intake valve heads. The ONLY difference between the two is the machining (larger valve seats, intake side relief cut).

Also, that relief cut isn't substantial but very necessary. I once cracked an L79 head. We replaced it with a correctly dated 1.94 head which was machined to accept the larger valves but we forgot to add the valve pocket relief cut. It never ran up to it's potential, always feeling flat in the power band. When we re-ringed it while it was still a fairly fresh rebuild, we discovered the oversight of the missing relief cut and added the relief cut back in before buttoning it back up. It ran very noticeably better after that! I was very surprised how much difference it made.
 
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