I work on big-block Mopar wedges w/ bore sizes in the 4.350-4.380" range (OEM 440 blocks). You may be aware it's not uncommon to find both as-cast and ported heads where the chambers have been opened up around the intake valves to approximate the corresponding profile of the head gaskets. However, typical bb Mopar head gaskets are flared out where the valves are, rather than staying true to the edge of the bore, thus resulting in a noticeable exposed ledge between where the combustion chamber has been unshrouded and the top of the block.

Some of the gaskets that are required to clear these unshrouded chambers already start w/ a 4.41 to 4.500 bore, and then are opened up even more around the intake valves, so this ledge where the top of the block is exposed is not insignificant.

If I was starting to rework a new set of heads that were cast so that edge of the combustion chamber was smaller, or no wider, than the bore where the valves are, would it make more sense to unshround the chamber only up to the edge of the bore to enable a smoother transition from the chamber wall into the bore, even if the flow #s didn't show as much improvement as when the chamber was unshrouded beyond the edge of the bore? Factor in that the top of the bore cannot be notched / relieved to reduce it, either due to the engine already being assembled, or the top ring location being only .175" down from the deck, thus restricting the amount which could be relieved.

This might be something that wet-flow testing could reveal issues re: how the air-fuel mixture is impacted by having to navigate past the exposed top of the bore, but I'm not equipped to do so. So, I guesss looking at it from a more common sense perspective is about all I can do. Thanks.

Really good question, I don't have an answer.

I hope Dwayne Porter reads this and chimes in. Fast68, where are you?

Or you could PM him.

R.

Notching the bores was done on early MW engines. Its not out of the question to do.

It's generally held that you don't want to sacrifice compression ratio for a few cfm of airflow either, but still, that being said, the BBM being a 15 degree head, you'll typically find that unshrouding to the bore size of the block is as far as you want to go because the valves are not far enough away from the deck surface that opening it up further will help with flow. If you're flowing the heads accurately on the proper size bore test fixture and not lining up the edge of the bore with the edge of the gasket sized chamber, I figure that the expected gains on a larger than bore sized chamber will be almost non existent and the loss in compression ratio will lower the engine's output more than the negligible increase in airflow will gain you. But, if you start messing with 23 degree chevy stuff, where the valve is up away from the deck surface a distance, and the valve isn't going to be shrouded from the cylinder for very long, going out to the gasket makes more sense, though at least beveling the edge of the bore on the intake side would be a good idea. I'm sure there are many trains of thought on this, this one is just mine.

Small block is 18, big is 15.

Here's a link to a book by Chuck Senatore because I had to look it up

http://books.google.com/books?id=6JIHWWW...gle&f=false

Love to help you but I just used up my 'Good' Answer on the previous question!!