No it is not vented to atmosphere. The car does backfire between shifts on occasion at WOT, but it also did this when I was N/A as well. The A/F on my car is at 12:1 and the rich condition does lead to backfiring once in a while.smashedheadcat said:I orded that valve but ended up canceling on it after further research. The reason I canceled is because of possible backfires. I assume you are "venting" to the atmosphere? If you are, does your car go pig rich for a split second and backfire?? That's just something I was concerned with. Any problems with that??