closed chamber vs open chamber

Open ----closed is referring to the combustion chamber of the head. Closed is smaller and a heart shaped(small combustion chamber, the open has the fill circle of the combustion chamber easily seen (bore of the piston in most cases). Nothing to do with intake......
By the way 516's as on the 67 383's are closed but use small valves, the 915 have large valves from stock and closed chamber. 516's are ok if you open up to bigger valves....more $$$$ is all.