Hi.
For those who are having problems with 100% atmospheric blow off valves, give the 50/50's a go, yes the problem will still be there as some of the air that has allready been measured will not not reach the engine, but it wont be as bad as a full atmo valve, plus you still get your "pchhhh" sound that you like.
If you really want the sound, and dont want to affect drivablility, just get a full plumb back Bypass Valve, and get one of those BOV noise generators.
This way you still get your noise, retain good driveability and it will end up being cheaper.
Jake