New Magnum heads for 347 with Flow data

Hebrews10:26 said

As far as seat inserts go they have been a positive influence on flow, not a negative.

The castings have major core shift issues 'why we have some that crack and some that dont'. A grinder to the short side will greatly improve them.

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I've seen it help and hurt. Its all in the execution of the seat used and the install job. Most of the circle burner guys that run "unported" Vortec headed Chevys won't touch the ones that came with hard seat inserts because of the poor mid lift flow.
I'd bet the seat install job on these heads created some mismatched ledges/steps for the air to run into. Nothing that can't easily be blended out though.