No it isn't capped. Just open to the air. Have about an hour and a half run time on it and no residue has appeared from it. When I mount it in the plane inverted I may see some then. We will see. If I do I will put a fitting in it and run a hose to a velocity stack in the carb. Saw someone here on RCU do that. I made the pipe and flange for the header and tonight I will Alumiweld it together and run it again to see if power increases. Than I will make the intake manifold with a taper and run that too to see if it gains any.