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JFairman JFairman is offline
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Join Date: Jul 2006
Location: S. Florida
Posts: 7,289
A side effect of blow off valves that vent to atmosphere is during long decelerations like going down a hill intake manifold vacuum is high and so is the inside of the intercooler so the blow off valve is fully open but there is no turbo boost because the throttle is closed and the turbo has slowed way down.
The result is the blow off valve is under vacuum and starts sucking in unfiltered air that may be dirty depending where you're driving.
Some blow off valves like the 25 mm 964 turbo type recirculation type valves can be mounted to vent to atmosphere instead of into the rubber elbow hose and then you can install a small K&N type air filter on the end of it so it filters the air being sucked in when this happens.

With the very nicely made TIAL type blow off valves with the air exit slots around the sides there's no way to put an air filter on it.
Old 04-23-2014, 07:38 AM
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