Sealing the combustion chamber.

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SG4029
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Joined: Fri Jan 07, 2011 10:44 am

Sealing the combustion chamber.

#1 Post by SG4029 » Sun Jan 09, 2011 10:18 am

I've put a couple of years into upgrading my car to run a heads up class on nitrous. Now I'm having trouble sealing the head gaskets in the area between cylinders. I have 15:1 CR JE Nitrous Pistons, 1/2" head studs that torque to 90 lbs/ft, copper gaskets with "O" rings in the block and receiving grooves in the heads. I've been told to abandon the copper and fill the grooves with copper wire and flatten it. Then install MLS gaskets. I asked Cometic about this and the answer was their gaskets are designed to be installed between two flat surfaces and they didn't know if it would work or not. I used to run Felpro gaskets before I went to so much cylinder pressure and never had a problem. Maybe I should just go back to them but I don't know what to do about the grooves in the block and heads. This is 567 CID, Merlin Block, Brodix Pontiac Pro Stock (10045427) heads and I want to run 2 stages of nitrous, 250 HP on first then up to 600 HP on 2nd. Anyone with experience in this area is invited to comment. CDR Performance should have good knowledge about this from working with blown stuff. Thanks for any help you may contribute, Gordon.
Last edited by SG4029 on Sun Jan 09, 2011 9:59 pm, edited 1 time in total.

71Hellride
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Re: Sealing the combustion chamber.

#2 Post by 71Hellride » Sun Jan 09, 2011 8:27 pm

I run the cometic mls gaskets and have never had a problem with them on my bbc. I've seen guys do the copper trick you are talking about and seems to work fine. How much are you spraying on it when it pushes the gasket out?

SG4029
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Re: Sealing the combustion chamber.

#3 Post by SG4029 » Sun Jan 09, 2011 9:57 pm

I have to clarify what's happening to answer your question. We've been trying to get the thing dialed in and running right on a 300 shot but that's not what causing the problem. It has been doing a lot of missing and backfiring because of a defective fuel pressure safety switch that makes and breaks. I'm sure this is the root of the problem but I am seeking info on the best way to seal the chamber before I waste another season with this problem. I have the "O" ring grooves, does that mean I have to stick with the copper gasket? I am looking for racers/builders that have done things to improve and can speak with first hand experience.

mytmouz
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Re: Sealing the combustion chamber.

#4 Post by mytmouz » Mon Jan 10, 2011 2:06 am

The cometic gasket will require a different surface finish. I have not seen the flattened copper wire, so not sure if it would work. What worked on a friends set up when he switched was a steel ring machined to the correct height installed in the groove. The machine shop that refinished the deck/head surface said it was OK. Held up fine so far. And I would ditch the Hobbs...
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CDR Performance
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Re: Sealing the combustion chamber.

#5 Post by CDR Performance » Mon Jan 10, 2011 5:31 am

Make sure your heads ans deck have a very low RA. Mirror surface.

Fill the o-ring groove in the block with some dead soft copper wire and flat file to the deck.

We prefer the FelPro MLS's. Before installing spray some copper spray or Hylomar between the layers and on the surface.
Hang the gaskets vertical to tack up and prevents puddles. The spray is very important at the front and the back of the gaskets at the oil drain back holes to prevent oil seepage. Also add a small bead of the right stuff along the china rail to help squeeze the gasket along the upper outer corners. (more oil control)

Check the heads also. Deck thickness, Straight? Depending on the head and previous work done to them. Many old Pro Stock heads have been worked on to much to contain boost or the pressure that N2O creates.
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Moparious Maximus
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Re: Sealing the combustion chamber.

#6 Post by Moparious Maximus » Mon Jan 10, 2011 9:03 am

I will admit I dont know jack about nitrous bit I'm surprised you are having problems with the O-ring/reciever groove and copper gasket setup, thats the standard for every top fuel engine out there and it works for them.

That 90ft-lbs seems short for a 1/2" stud, we torque our 7/16's to 85 lbs, copper gaskets love clamp load.
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SG4029
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Re: Sealing the combustion chamber.

#7 Post by SG4029 » Wed Jan 12, 2011 10:42 pm

Been thinking over the comments and they are all good. I have to tear the engine down again to do some checking. Have to see if I had a lot of leakage after the last runs. Leakdown first, then disassemble. probably next week.

Mytmouz: Thanks for the response. I know mls gaskets require a smooth surface, but I don't know about trying to make a steel ring that big (diameter) and so fine (wire size). I need to use the .041 copper wire, I guess. And the Hobbs is gone.

CDR Perf: That's basically the same direction I am receiving from other engine builders. You went a little further explaining treatment with copper spray or Hylomar. Thanks for that. I've always used Hylomar, think I'll stay with it. I'm assuming the China Rail is that portion of the block that extends up to the manifold on the block ends. Thanks for the input.

Moparious Maximus: I have to agree with you that the setup I have should have done the job since that seems to be the preferred way for so many blown cars. I'm sure I don't make near the cylinder pressure most of them are generating. But your comment about stud torque has me thinking hard. Maybe I should be going up around 100-120 lbs/ft, or more? ARP told me 90. Clark Copper Gaskets checked with Buck Racing Engines for me and they said I had done everything right if the block and heads were flat. We did all that right so I don't think that's the problem.

Clark also recommended the 1/2" studs. He said I had to prevent head lift. Now that I've pondered this long enough and I have the comment from CDR Perf. about the heads deck thickness, I think I need to relook that area where the gasket is thinest between the cylinders. There is a stud above and below that area, but if the head is too thin on the deck I can picture it pushing up toward the water jacket and releasing pressure on the gasket. I'll check deck thickness real close when I get them off.

Thanks for all the info. You guys are a big help.

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CDR Performance
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Re: Sealing the combustion chamber.

#8 Post by CDR Performance » Thu Jan 13, 2011 7:06 am

Fasteners.

ARP rates their fasteners at 75% or yield. You can exceed this at no more than 10%.
At a greater tq value the fasteners become a one time use item and must be disposed after use.
Also if tq'd too close to the yield the fastener may fail during use.

Good luck.
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SG4029
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Re: Sealing the combustion chamber.

#9 Post by SG4029 » Thu Jan 13, 2011 9:58 am

That's what I call good info. 10% is 9.0 so I can go to 99.0 lbs/ft without a problem and still reuse the fasteners. I don't want to get into a throw away situation, they cost me over $400. I think I'll just stay with 99 and call it max but safe. Thanks again.

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