Thread: Got a 478...
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Old July 2nd, 2022, 12:53 PM
Prowbar Prowbar is offline
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Join Date: Dec 2020
Location: Friesland, the Netherlands
Truck: 1965 GMC 1500, 478 V6, SM420
Posts: 383
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Prowbar is a jewel in the roughProwbar is a jewel in the roughProwbar is a jewel in the roughProwbar is a jewel in the roughProwbar is a jewel in the roughProwbar is a jewel in the rough
Default Re: Got a 478...

Cleaned up the major grime off the heads. Removed the valves, no surprises. The valve springs are pretty stiff though. The guide from the burned exhaust valve needs to be sleeved, as it has more play than the others.

I will also have the heads professionally cleaned, decked and have hardened seats installed in the intakes.

The castings, as from the factory, are pretty bad regarding port design. The exhaust passages faily are restrictive compared to the intakes. But the worst thing is the short turn into the into the head has a very sharp ledge above the valve seat. I am working to radius these to create better airflow. Both intake and exhaust have these sharp ledges. Also the exhaust ports really need to be cleaned up, they have ledges in them. I removed these also.

I also lightly broke the sharp edges in the machined combustion chambers.

That's as far as I'm gonna go with the heads.
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Last edited by Prowbar; July 2nd, 2022 at 12:58 PM.
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