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CNC is repeatable, but can't take advantage of making the port as big as possible because of casting shift.


Why would you want the ports larger on core shifted heads?



That's the point. CNC programs have to work on every single head, even the one's that are core shifted. That means the programs have to be conservative (small) to account for core shift. A hand porter can take advantage of a good casting...



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A good hand porter can feel/hear when the walls are getting thin.



Really?
Now thats a skill I would love to know..Im sure its possible at the point were its almost through the side of the runner...LOL..
But at this point the heads are trashed anyways.




I kid you not, a good head porter can hear when the port wall is getting too thin. You can hear the grinder bit change pitch. I suppose grinding on heads 10 hours a day for 20 years will do that to a guy.



so i guess the head porter that did my heads wasn't listening too good,leaked like a dyke.