they are Edelbrock aluminum covers, I think (I'll check) they have baffles, and a push in breather. Don't think it could be blow by. If I take a hard right at high rpm liquid oil goes up into the breather and dumps oil down the valve cover and header. To me it seems the valve cover is filling right up, at the back anyway because of poor drainback, maybe it has a high volume oil pump? Motor was done when I got the car and has low miles, doesn't burn oil, or have blow by.