I have to say I removed the original pipe to the air duct as I found quite a lot of traces of oil in the duct on numerous occasions, which would suggest the intake duct was drawing air from the valve cover. I got rid of it because I obviously don't want hot oilly air being sucked into my IM. But then I imagine when the throttle body is closed, the pressure in the duct was causing air to be forced into the valve cover.
We know that the PCV valve connection and pipe only sucks air from the valve cover into the IM (hence why people fit a catch tank), so the breather pipe (air duct side) will obviously need to allow air into the valve cover to insure a vacuum isn't created, but then when you're in WOT and they're both sucking this is going to create a vacuum surely? So I'd have thought fitting a breather filter was a good thing as it can simply draw air in and out as the engine pleases. The only issue I could see is that the inside of the filter will get clotted, so it's probably best to change them quite often... Or better still, fit a catch tank that side as well.
Thoughts?...
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I cant wait to see how much power she'll be putting down.