when boosting. This might indicate that there is cooled air setting in the intercooler that is pushed out when you boost. The air flowing thru the intercooler prior to boosting was probably shooting thru just the center of the intercooler and the air in the top of the intecooler was setting there getting cooled until you boosted. One theory I have is that with big, low restriction intercoolers and small ducting, the air short circuits much of the intercooler, and just shoots across between the inlet and outlet.