B.O.V's are worthless on a stock or even a slightly modded WRX setup. Too much stuff goes wrong. I ran a Greddy Type-RS on my 2004 and it worked great for the first....10 min. and then stuff started going wrong. I wasnt hitting target boost, compressor surge in 1st, 4th and 5th around 10lbs Boost., bogging while shifting (more spool up time than without BOV) If you really want that loud ass sound and want to be like every other rice burner who watched the Fast and the Furious and willing to risk the performance value of your car, then sure, BOV it up. Or you can go the way of the WRX Samurai and do Up-Pipe, Downpipe, Drop in Filter and REflash to Stage 2 and still get the BOV sound but not alerting everyone around you and the police. All a BOV does on a stock or slightly modded WRX is say "Hey look at me"!
But, I digress. A 3-Liter bottle cap with a hose clamp should work just fine.
