Joe-JDC.  WoW!  That was some serious reshaping of the 'G' cylinder head combustion chambers that was done before Cliff purchased the heads!  Combustion chamber volume must have grown significantly with having done that.

Joe, I JUST received my USPS delivered September- October issue of Issue 154 of Y-Block Magazine late yesterday  (12/10/2019)!  Ted did a great job of detailing what you two experienced in participating as entrants in the 2019 Engine Masters Challenge.  The 10 page write-up Ted put together was both interesting and informative.  Again, kudos to both of you for your efforts and accomplishment.      


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

Now I get it! Thanks Joe and Ted.

"FREE SAMPLE"

 
The simple answer is that all you have to do is grind the metal around the whole circumference of the valve to get the flat indention left.  It is called total unshrouding of the valves, and is not necessary, but once the metal is removed, it can't be put back cheaply or effectively.   Joe-JDC


JDC

I don't know, the work on these is nice, I just think it's old thinking, i'm going to spend some time on them and see where I end up, I would have never done this kind of work however we'll see, maybe it is the way to go, who ever did this was no dope, the work is to nice, the chambers look perfect, the exhaust still has a small amount of guide showing, I'm surprised they have stock valves, the brass tubes are flat sheet stock rolled to fit (you can see the seams), so far the flow is poor for all the work done.   

Here's what I'm talking about. I've never seen G heads with that odd flat sided protrusion opposite the spark plug! The G heads I know and love
have combustion chambers like this;
: the



"FREE SAMPLE"

Ted is right, the combustion chambers were relieved around both valves thinking it would increase flow, but not true.  Some folks think lowering the compression by unshrouding the valves that way is best for supercharging applications.  I have seen many changes over the years in thinking, and that is very "old school" way of finishing the combustion chambers.  It will work, but not the absolute best.  The heads will probably work just fine, and make good power with slightly larger valves in both positions.  The issue will be cylinder head gasket sealing if the chambers are too big to be used on a smaller bore block.  Joe-JDC

JDC

 
Ditto on the question about the protrusion in each combustion chamber.  Looks like its a reasonably consistent modification regardless of why they are there.  In looking at the chambers in more detail, it would appear that the protrusions themselves were not a added feature but material that was not removed when enlarging the combustion chambers around the valves.  While the chambers around the valves were enlarged to enhance the flow, I would surmise that the protrusions were left to help keep the compression ratio from being further reduced.  What do you think Cliff?

Lorena, Texas (South of Waco)

Cliff & Joe-JDC.  Thanks for your replies to my question about cylinder head porting. 

Joe-JDC.  Kudos to you and Ted on what you accomplished at the 2019 EMC event in September/October.with the 303 y-block entry.  Well done!


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

Hi Joe, I think you are right, for the amount of work someone put into these heads I would expect better numbers, they look like bigger is better, however they were cheap, I will do more work on them and see what I can do, I also did a fast check on the bench, so these numbers may not be correct, I ran them with a 3.860 bore, I only checked at .550, it was 65 deg. in the shop, I did no error correcting.  

PS my bench is so noisy I don't think I can hear a noisy port (JKM 600)

As someone who has ported cylinder heads for 47 years, it has been my experience that taking the guide out flat like that actually hurts flow, causes turbulence, and a very noisy port because of the turbulence.  It also removes some of the stabilizing of the valve, and cooling area for the stems, especially in the exhaust.  Another thing that will cause to happen is a siphoning of the oil from the guides.  If the exhaust is cut a little wrong, it will actually pressurize the crankcase some and coke up the valve stem into the guide and wear much faster.  A simple fix would be to install tapered iron guides, or bronze guides.  Problem solved.  Joe-JDC

JDC