Blow Off Valves Bad?
100% atmospheric release blow off valves cause your engine to run rich for the split second you let off the throttle and the BOV is releasing pressure. It runs rich because the engine is expecting the blow off air to be returned through the turbo inlet hose and into the air intake. This rich condition causes “AfterFire” and in exhaust systems with no catalytic converters a flame can be seen to come out of the exhaust pipes anywhere from 2″ to 2 feet depending on temperature of the exhaust pipes and how rich your car gets. A blow off valve installed on a car with modified exhaust and intake is OK. A blow off valve installed on a stock wrx is BAD. The afterfire will have nowhere to go due the catalytic converters and will expand in your turbo rather than out your pipe to produce the ever wanted “pop” from horizontally opposed turbo engines. This benefits off road users because it allows the turbo to stay spinning longer by releasing the pressure out of the system rather than back into it
