For your viewing pleasure.
These are a set of 991's I started to port but gave up. They were 1.72"(valve dia.) intake heads and I got worried the port walls would get too thin by the time I opened them up for 1.94's so I scrounged the 441's and gave them the same treatment.
Bear in mind these heads are not finished so the finish wasn't smoothed. I wanted to show you how to split the air around the guides.
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This pic kind of shows how you can relieve the chamber to allow more air to pass by the head of the valve. It hadn't been done yet but basically you match the radius of the valve head as much as the head gasket will allow.
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Here you can see how restrictive these heads were in the bowls especially the exhaust ports.
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These heads have nice,tight valve guides and no cracks but even after opening them up for the larger intake valves I feel they would have hit a wall at 5000 RPM. Probably should toss them in the scrap iron pile but they would make emergency spares.