I am just trying to figure out if the exhaust valves on a header should allow air/ fluids to go through it, meaning does the valve have a perfect seal with the header. I poured brake cleaner down the valve and 3 out of 4 were leaking it out slowly. is that normal operation for the heads or the exhaust and intake valves should both have perfect seal ?
I think you are asking if a valve in a head will seal out all of the fluids and air? The answer is yes it should. A leaking valve will not hold compression if this was the case. The valve should have a perfect seat seal and not allow anything to pass until it is open.
If you need assistance with identifying and fixing your leak get some help from a professional mechanic who can diagnose your leak and make the appropriate repairs to ensure everything is operating as it should.