Thread: Turbo Issue
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Old 2011-05-04, 12:24 PM   #67
sperry
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Real Name: Scott
Join Date: Nov 2002
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Car: '09 OBXT, '02 WRX, '96 Miata
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Quote:
Originally Posted by Dean View Post
High on the firewall is better for a catch can than at battery level IMHO. The AOS doesn't care since the oil dumps back into the sump, but in theory you want as much oil that collects in the hose to drain back where it came, not into the can.

The single line (vertically) on the AOS returns to the intake.

If you think about it, there should be no pressure differential anywhere inside between the block or heads since they are all connected by huge oil galleys that flow way more than any hose could. My belief is that the majority of the people with catch cans that filled up where not due to the alleged pressure issues, but bad downhill hose routing to low mounted cans.
I think the problem was more an issue of hose diameter allowing the heads to effectively become the path of least resistance for crank pressure. So you would get a ton of flow from the crank into the heads and out the breathers that pick up a bunch of extra oil. If the crank breather is big enough, blow-by pressure can go out the top of the case instead of pushing out the heads.

At least that's my theory... after 10 years of farting around with this stuff, I still don't claim to really know how it all works.
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