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Old 05-21-2017, 05:38 AM   #26
Scooby Newbie
Member#: 467995
Join Date: May 2017
Location: Australia.
2003 Club Spec 6.
World Rally Blue.


Yea, it's all in the bov.

Wrx came stock with a bov. It's recirculating, not atmo release. A blow off valve is a blow off valve. Where it vents to is either plumb back, (stock subaru setup), or to atmosphere.

Ok, the bov mod bypasses the internal spring being a safety of sorts and limiting boost pressure. It makes the oem bov the same functionality as aftermarket ones, but you get to keep the reliability and no leaking of the stock subaru bov. Win.

Start here:


Then you need to make a reference to atmosphere hole as well, which I have covered here on my own bov:

That's a 1.5mm hole in the tube above where the grub screw goes in. I placed it here as when the bov is installed it is facing down away from any possible water ingress. The guide has it on the section you see to the right of my hole, the hump part. That is facing up when installed and I didn't like that.

Only bother if you are running high boost and your bov is holding you back. And be careful as the material is soft. Take care to clean all shavings out and to only go through the outer wall when drilling the reference hole. The stu stu is just a side effect that you cannot avoid, not an intentional design as it will still vent when manifold pressure falls below intercooler pressure, but until then you get surge. I also found that with mine at least it doesn't sneeze anymore either as the pressure is not as high when it does vent.
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Last edited by mv75; 05-21-2017 at 05:44 AM.
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Old 05-23-2017, 08:18 PM   #27
91 RS RA
Scooby Newbie
Member#: 457410
Join Date: Oct 2016
Chapter/Region: International
Location: Christchurch, New Zealand
1991 Legacy RS RA


Have a watch of this ( if it hasn't been posted yet, If so sorry for double posting)
This will explain everything you need to know about this

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