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I've heard several times of the guys that port by hand breaking thru as well.

The guys that CNC port heads should have equipment at their facility that can sonic check or x-ray heads prior to machining as an extra precaution.


Based on some spots where the rocker shaft hold-down bolt threads are showing through on my CNC-ported heads, I'd say don't bet on it.

Sh!t happens, either when grinding by hand or w/ a CNC program on a casting w/ more core shift than anticipated.

Don't forget that just because a port design is available in CNC doesn't mean it's a GOOD port design, only a more easily repeatable one.