[Formulabruce]

Originally Posted by Rocky Rotella

Why would you need to angle mill a round port head to get it into the 98 to 100 cc range?

The 455-inch round ports have large, open chambers and volume can be reduced by 1 cc for each .005-inch cut from the deck surface. Removing .060-inch from the deck surface would reduce combustion chamber by 12 cc.

Using the .005 inch-for-1 cc formulation, we successfully reduced the chamber volume on a set of 7F6 castings from 108 cc to 100 cc by removing exactly .040-inch from the deck surface. We poured the chambers before and after, so we could be absolutely certain we were at our target compression ratio. Having known they were milled slightly during a previous rebuild, and that was likely .010 to .020-inch at most, the 108 cc we started with makes 110-111 cc a logical starting point in original, as-cast form.

The 7F6s have a chamber shape practically identical to the SD-455 16’s. The seller claims “about 98 cc” for his SD-455 heads in the eBay auction, and that seems like a reasonable amount to me when considering that Dave Bisschop likely milled them .050 to .060-inch.

While popular on certain other makes, angle milling isn’t overly popular in the Pontiac world. With that in mind, angle milling could present a host of other issues most Pontiac hobbyists might not consider. Besides milling the intake and exhaust flanges an equal amount in opposite directions, depending upon how much angle is milled from the deck surface, it can require elongating the cylinder head bolt holes, modifying certain coolant ports, and relocating or modifying the dowel holes.

While the photos can make it difficult to see all those points, I don’t necessarily see anything that would indicate these particular castings were angle milled. I think these are nothing more than a properly ported set of SD-455 heads that have been cut to a maximum of .060-inch on the intake and deck flanges and will install on any engine without issue. Am I missing something obvious?

Thanks for that, Obviously I really wanted an explanation of what was done, and I am more familiar with getting more cc with angle milling ( on other gm brands) I have been screwed by that a couple times. So consensus is that ,the intake , a person would use with these would need to be be milled and port matched? Question stands, can a stock SD intake or a performer go on these ? Thanks for all the input