Found this on Cleveland Heads:
Even though a Cleveland head had great flowing attributes, they still received serious modifications. That’s why they were so dominant back then.
First, the exhaust side had 1.400˝ milled off. An aluminum plate that thickness 2 5/8˝ high was bolted in place relocating the exhaust ports higher. This was known as high porting. The original iron part of head port was welded or brazed and recontoured to match the plate port, making the exit as smooth and straight as possible. The longer you could keep the primary header tube straight off the port, the better the flow. A 19˝ long 1˝ wide X .250˝ thick steel girdle was used on top the aluminum plate. Torque sequence and poundage was also altered.
The intake port also had radical modifications. It was ported to the max flow and the pushrod boss cut through. Then braze or epoxy sealed that area. The intake rocker studs were moved over .250˝ to the right along with the push rod slot. The guides were plates cut, rebridged and welded.
Then blades were carefully installed in the port entrance to calm the turbulence. That blade installation had to be done on a flow bench. If placement was not perfect, it could ruin the efficiency.
Then we had offset dowels to index the head. We reinforced the headdeck by posting. Posting was drilling, tapping and installing 1/2˝ studs into the larger open areas in the head’s deck against the roof. Then mill the deck smooth.
Another must were the 3/8˝ load bolts from the outside ends of the heads through tapped holes nestling against the thin intake seats on #1 and #8 to keep them round. The work done in the combustion chambers was an art form. All was handwork. No CNC.
There are also things called: Roush type 351C-4V port stuffers. Essentially giving you raised port heads in factory style castings.
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