The shrouding is going to be the most sensitive issue that you face. If your machine shop hits water, it is only because they plunged too deep with their cutter. Thats the most common mistake that people do when putting larger valves in these heads. For some reason they think they have to sink the valves a mile by installing them, but they also kill the short side radius even more by doing this. Thats a lot of the reason they don't see much flow gain by going to the bigger valves in the first place, they ruin the head from the get go, and are disappointed when they dont see the results they thought they should get, not realizing the machinist is too blame. Don't forget to open up the bowls accordingly, this too is often overlooked and doesn't get the maximum bang for the buck for putting in larger valves either.
