Our cars need that recirculated air. Read below and follow link for a little more info.
"It all boils down to whether or not your car runs on speed density or mass air. If you have a car that is speed density, you will not have a mass air meter. So, effectively, you can run a Blow Off Valve which give off a very loud WHOOSH sound as you shift gears when in boost. A Bypass Valve takes that boosted air its venting, and recirculates it back into the intake. The importance of this on a mass air car is, that air was already metered and counted, therefore, venting that air to the atmosphere will cause your can to go rich. You are effectively removing air once counted and letting it blow in the air, so the car is going to add more fuel thinking that air is still incoming. Many enthusiast prefer the sound of a BOV, but generally they end up doing damage to their catalytic converters because of the rich conditions incorporated into running a VTA ( Vent To Atmosphere ) system on a MAF equipped car."
*link not working*
Hope this helps, you will probably need a tune or reprogram if you want to use a straight BOV, I have a turbosmart BOV and run it at 50/50 with no problems and I still get the awesome woosh sound.
