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Old 07-19-2013, 02:31 PM
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porting, gasket match question

This seems a bit much to gasket match, I would have to remove A LOT of material. Also I would have to removed a fair amount of the gasket itself in the middle in order to have it match the head. What should I do?
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Old 07-19-2013, 02:35 PM
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You don't necessarily need to remove a bunch of material, just open the mouth to the gasket size and blend it back smoothly.
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Old 07-19-2013, 02:39 PM
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I would only trim the gasket where it hangs over the ports like in pic two. I would be loathed to remove any metal to suit that gasket. Maybe another brand gasket will get you closer to the port size.



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Old 07-19-2013, 02:48 PM
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How does the gasket look on the head? If your going to 'port match' that's a different procedure. You need to blueprint the two surfaces together without the gasket and ensure that the head port is not smaller than the manifold port around the circumference of the port, the other way round , ' not so bad' Then make sure the gasket don't hang over anywhere. Depends how fancy your getting with the build.



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Old 07-19-2013, 06:44 PM
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Do not use those gaskets unless you have tubular headers because you will be tightening them constantly. If you have stock cast iron manifolds, they will not tighten and seal properly with anything but the thin factory steel gaskets.
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Old 07-20-2013, 11:29 AM
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Quote:
Originally Posted by Nuck Chorris View Post
This seems a bit much to gasket match, I would have to remove A LOT of material. Also I would have to removed a fair amount of the gasket itself in the middle in order to have it match the head. What should I do?
You are correct- that IS a lot to remove. Unless you're shooting for max flow by doing the whole length of the ports and not just enlarging where the head and intake meet, the best way to go about this is to match the head and intake ports to each other's largest port side. This is port matching as opposed to gasket matching, and is worth the trouble.

Hogging at just the juncture of where the head and intake meet- making a "snake that ate the pig" looking port- will decrease flow due to the turbulence caused by the airflow slowing where the port cross section enlarges.

Very early in my porting I had some success using vaseline on the flanges and gasket, then blowing talc through the ports from both directions. The talc adheres to the surfaces that are hanging in the port, this is used as a template to scribe a rough guide to follow. You can also plot the alignment using machinist blue and a scribe to show the alignment; this is a better, more exact approach. The idea here is to take each side, each top and each bottom of each port to whatever side (head or intake) is largest, and no more. That aligns the ports, and thus the airflow, w/o creating a bulge or an unnecessarily large change in cross section. I've seen tutorials on this, I'm sure you can find one w/a little looking around the 'net.
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Old 07-21-2013, 09:23 AM
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The important question here is how does that gasket "match up" the the headers you're using? If this is that same 350 you were asking about the cam/lifters, I'd say those "holes" are too big. The headers may be as well. A 1 5/8" header is called for. Felpro's header gasket for the d-port fits Hooker "Comps" and other smaller-tube jobs very nicely.

If the headers ARE 1 3/4" or larger, all is not "lost". The edge of the port that "hanging" in the flow path acts as a "reversion dam", helping keep things going along. So, while not "optimum", not nearly as bad as the reverse situation (header flange hanging into flow path).

Agreed, unless you ARE using headers, do NOT use header gaskets. The steel shims that come in full gasket sets work well with Pontiac manifolds.

Jim
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