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Old 04-26-2010, 01:47 PM   #1
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Default Modifying Headgasket

I swung by the machine shop this weekend to have the guy look over my DIY valve deshrouding and make sure I am doing the right thing. He commented that it looked funny how little I had/could modify the combustion chamber due to the limited space around the valve.
I traced the size of the bore opening on the head gasket onto the head and used this as my outer limit for deshrouding. I wish I had a picture of a deshrouded combustion chamber to make this a little clearer. Due to the location of the valves near the sides of the combustion chamber you can pretty much just open up the area above the valve and no where else.

Now to my question. He mentioned that they could use the ovesized cutters while doing the valve seats to cut clearances around the valves. The problem with this is that the head gasket would obviously protude into this space and thats just bad in so many ways. He then explained that I could get a custom made head gasket or modify the headgasket I have since it is a MLS gasket.

Has anyone messed with modifying headgaskets? Do the larger 84mm+ overbores still use a OEM spec gasket? I guess it doesn't seem impossible to modify the gasket, but there are just too many factors that I don't know about that can cause problems like creating hot spots or weakening the headgasket by introducing stress risors ect.

My machinist is great but 99% of what they do has 8 cylinders and a oval or bowtie on it. I know they do stuff like this on those huge heads with lots of space all the time, but we do not have large cylinder bores or room to make all these modifications.

Im really not looking for a "thats a good/bad idea", just has anyone done it. I'm hesitant to do it, but it made me wonder if it has been done.
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Old 04-26-2010, 07:56 PM   #2
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I think modifying the head gasket is a bad idea, however there are oversized head gaskets for the larger bore pistons. Check FM's site, stock is good for stock or +1, and they have others for bigger bores.
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Old 04-27-2010, 11:36 AM   #3
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Here is a picture that might clarify what I am talking about.



The blue circle being the lince scribed from the inside of the headgasket. The red circle representing the size of the area to be deshrouded. It would only need to be 2-3mm past the location of the factory head gasket. Opening this area around the valve up will greatly deshroud the valve and increase flow. I know we are talking about very little total gains, but I am just speculating and trying to see what I can do while I have it all apart.



I know it still looks rough and isnt finished yet, so please don't rag on my porting work.
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Old 04-27-2010, 01:10 PM   #4
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I have seen this cylinder heads in stock form perform very well even on cars running 10/11 second passes.

If I were you I would stay away from doing that mod. Many of those V8 CH flow terribly so thats where it all started the deshrouding deal, also make note the compression (as you stated will not be much) will be affected.

The only mod I have done on a headgasket is removing two layers to raise compression and open (dremmel) one of the water ports in the HG. I swapped to a Kia CH and one of the water runners was drop shape instead of circular, never have had any leaks and that was around a water port.

Yours right around the piston chamber where so much pressure is goin to be seen, mmhh... dont know.
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Old 04-27-2010, 01:23 PM   #5
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I believe that JasonS CCB modified his headgasket to go on his 01+ engine, but it was simply opening up some coolant holes.
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Old 04-27-2010, 01:34 PM   #6
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I figured that would be the case. I also did not feel too great about removing gasket strength in an area that is so close to the oil and water openings.

I will just leave it as is. As far as the compression changes, I am shaving just a hair off to compensate for it or leaving it as is. I will probably shave of fjust the minimum possible to get a fresh surface for the head gasket to grab on.

How much would shaving 2-3 thou off the head change the compression ratio (currently the NA 1.8 9:1)?
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Old 04-27-2010, 01:46 PM   #7
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You should take a look at the head gaskets offered by Chikara, many options available:

Chikara Head gaskets
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Old 04-27-2010, 01:56 PM   #8
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you could Get a "dead soft" copper gasket made that is any shape you like,Another V-8 trick.I dont know what the longevity of these gaskets are,I had one on a 500hp.383 c.i. Chevy that lasted a few years.
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Old 04-27-2010, 02:01 PM   #9
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I was looking for a place that did the custom gaskets like that. A 86mm gasket would give meroom to open up arount the valve. Other than the reduced compression due to the slightly larger combustion chamber volume is there anything else that would prevent me from running a 86mm gasket on the factory size bore?

A copper gasket would be easy to work with but I doubt it will last with my future turbo aspirations.
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Old 04-27-2010, 02:07 PM   #10
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What the hell!
Chikara wants like 225CAD for the headgasket but then wants to charge 1500CAD for EMS shipping but do not offer any other shipping options. Thats nuts!
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Old 04-27-2010, 02:33 PM   #11
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LOL, What da?

I did not notice that part, I thought there was a glitch with the website, man what a rip-off.

Well, Like I said on one of the postings, I did port one of the holes in the stock metal head gasket, see if I take pictures to show the difference and always worked fine, no leaks etc.

IMO a good machine shop can open it up just a little, to me the OEM one has high tolerance as I ran it with two plies instead of the typical 4-layers, opened the rivets a little, removed two layers, and hammered the rivets back, it sounds ghetto but it worked.
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Old 04-27-2010, 02:55 PM   #12
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Quote:
Originally Posted by relte View Post

A copper gasket would be easy to work with but I doubt it will last with my future turbo aspirations.
Are you kidding,What kinda gaskets do think 7,000 hp TF dragsters run?They will hold all of the boost you can throw at them,I just dont think they have the 100,000 mi. durablity that we often require.They need to be retorqued on a basis,and IIRC they need to be replaced at 50,000 mi.Coppper is one of the best gasket materials.
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Old 04-27-2010, 03:23 PM   #13
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To OP. Are you planing to port the top of the bore too? The cutout area you show in the pic will go past the bore hole. There is probably little gain to be had there anyway, being on the short turn side of the port. I would rather have the quench area than the marginal flow improvement you might have made.
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Old 04-27-2010, 03:59 PM   #14
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Alta, that is what I was waiting to hear. I don't think it will be worth opening the can of untested worms so I will leave it as is for now. Just wanted to see if anyone has messed with this before.

I didn't know that about the copper gaskets, Sorry. My first car blew a headgasket and it was the onlt car I had with a copper head gasket and I think that has just put me off since day one. I always thought they would work great, like the crush washers do in a banjo bolt. Its softer than aliminum gaskets so I can see it working I guess. Especially for less than perfect sealing surfaces. Arn't the copper gaskets usually thicker as well?
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