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Home » Public Forums » GMCnet » replacing driver's side head on a 455 (Jumping into unknown waters and any help appreciated)
Re: replacing driver's side head on a 455 [message #362831 is a reply to message #362723] Mon, 15 March 2021 12:48 Go to previous messageGo to previous message
rgogan is currently offline  rgogan   United States
Messages: 82
Registered: February 2004
Location: Milwaukee, WI
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More info obtained an how to manage the head exhaust center port webs:
The knowledgeable person who privately responded to me highly recommended building the divider out flush on the Olds center exhaust port. It is done by putting a weld bead down then machining it flush. Here is the rationale:
With the use of headers, the value in exhaust breathing improvement and cooling comes from having one pipe per cylinder. The merging effect at the collector will aid the pull from each pipe. If the web is not built up, the value of having headers is not fully realized. Simply removing the divider in the header gasket might prevent the gasket from blowing out, but it will just allow exhaust gases to bump into the divider in the header and not provide the separate pipe for each exhaust port.

I have purchased the aluminum intake manifold designed after our original GMC motorhome low profile cast iron design with modifications for clearance of our carbs. It eliminates the original intake manifold exhaust cross over.
Next question:
What is the best gasket to achieve a leak free seal in mounting that aluminum manifold? Applied GMC seems to have a gasket without the crossover port in it which seems idea. However, is it better to install the gasket with the stainless steel crossover port plates to keep the gasket from deteriorating from the hot exhaust gases or is this not necessary?

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