[Alan Roehrich]

Everything you do to the valve seat or the bowl must be concentric to the valve guide. There is no written limit as to how deep you can go, or how many angles you can use. Be aware you can cause yourself problems with runner volume on certain heads. And use common sense with regarding to how deep you go, because I don't think they'll go for 5/8" or 3/4" deep and cutting around the valve guide.