I'm sure some of you guys have tried this but its something I tried years ago after talking to an engineer Friend of mine. I was working on a set of heads that I knew were capable of more CFM so I asked him if there was a compound I could use to make a mold of a head port. He hooked me up with a company he used in the past for such a project. I tried it and it works like a charm and has paid big horsepower gains plus it made it so nice to see your work in 3D. It also makes it possible to take my work into the house so I can search for issues that I can fix the next day in the shop. I spray the inside of the port and mix up a batch, Of coarse the valve is installed and the head blocked so I can fill it from the intake face. I usually give it at least 36 hours before I remove it. kinda cool looking at your work from every angle.