Why people recommend those open chamber heads is always a mystery to me. It might be the listing that edelbrock has that confuses the crap out of their buyers. Harder to build a quench engine with them. That's why the closed chambers are the better option. Adjust quench with your head gasket thickness especially if it's a zero or positive piston height. First thing I do when I get a set of those open chamber heads... they go on a surfacer to get rid of the open chamber.