Would someone please tell me the purpose of the "nub" in the combustion chamber between the spark plug and the cylinder. The heads are the alum. 113's, s/a zz4, thanks.

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Interesting question. Is it for strength for the hole underneath? Just a casting flaw because it was easier that way? I'd like to know now, too....

Matthew

its not for strength.. that is from what i have read the thinnest area in the chamber.

as far as I know it's a machining part for the factory equipment.

2 sets of zz4's (same casting as the 113) on eBay. One set has it, the other doesn't(ground off?). I am working on these heads and need to find out if grinding this projection off will benefit combustion. It certainly doesn't look like a power adder. The carbon spot in the chambers should tell me something. Need to do some legwork.

I had a set of 113 heads ported by Precision Motorsports in Florida, and that nub was not there that I can remember. I think they either severely smoothed it out or completely removed it. Wish I had pics but I don't.

David Vizard also suggests to remove them in his book on modifiying SBC cylinder heads.

I have removed them completely. You can see it here:
http://www.corvette-guru.com/modules/ ... id=117112#forumpost117112

Thanks y'all. Sliding, I looked everywhere for any info. on those nubs. Everywhere except Vizards book, I guess. I'm porting a set of used 113's to swap onto my '91. Maybe I'll start a new thread with a few specs and pics. Still wondering exactly what their purpose is, or was. Maybe it is a vestigal machining piece, but I find that hard to fathom.

I'm also really not sure why it's there, but I'm sure that it doesn't help combustion. Anything of that shape has nothing to do in a chamber.

Anyway here is a pic fron Vizard's book:




It's from the book below. There is not very much info
specific to #113 heads but it's OK book to read.

Quote:

The heads I got from you? I took pictures. They didn't do much in the combustion chamber. I have them off and was thinking of touching that area up.

[IMG]http://i119.photobucket.com/albums/o130/Aardwolfki/Porting/head4.jpg[/IMG]

It could be there to have something to do with keeping the plug at an even temp. Not having it fouled or cooled by gas.

Hmm, kind of a heat sink. That makes sense. Well, if my calculations are correct the volume of that piece is only .375cc which will have a negligable effect on compression.

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Yes, those heads. I stand corrected, the nub is still there. I remembered it on my stock heads but when I bought those ones I didn't remember it there. I had talked to them on the phone even though the heads were done when I boutght them, and removing that nub is one of the things they do, but there are different levels of head work they do depending on what you pay for. I guess that wasn't paid for when these heads were done.

Yes, I would think removing that while they are off would be a good idea.

They also told me they removed .006 from the heads to clean them up. I never had them shaved, so that should be all that was ever taken off of them, if you are considering on having them shaved at all. After that .006 was removed, they were installed and removed, then sold to me and installed and removed, then sold to you and installed and removed, so it might be a good idea to have them checked for flatness before reinstalling.

I took them along with me when I dropped off the short block. My builder thought they should be done again, a .005 shave he was thinking.

Not a heat sink, an actual block to prevent fuel from going onto the plug. I don't know for sure if it's there because of a wet flow issue or not. I'll ask my builder what his thoughts are.

I seem to remember being told that it was there to create turbulance around the plug which would enhance mixture burn in the combustion chamber.

If you look at how it's situated in the combustion chamber (offset towards the intake valve) that makes sense.

Back in the 80's when Vizard wrote that book, we all made our combustion chambers look like a "bath tub". It was more about unshoruding the intake valve to get better flow numbers and making room for the huge dome pistons we ran to get compression with the 23* heads of the time....

It worked OK back then - but we have moved toward "double quench" combustion chambers which offer far more efficient flame travel with flat top and reverse dome pistons.
Will