those are actualy backwards.
if you look at the blow off version of this valve you will see that the opening on the SIDE of the unit is the one meant for air to release.
also if the air is going IN from the side the buildup of boost will not be able to push the piston up to help open the valve, it will be hitting the side and will nto help it. The valve will still open from the vacuum line on the top but it will not responde as fast and if will most likely flutter a lot.
Modified by Cass944 at 9:32 PM 11-24-2006