Vacuum from manifold would suck some oil out of sump

using the Perth-WRX mobile app

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MY08 STI 422whp at 1.5bar on E85, built by Diversion Garage, assembled and tuned by EvoR

Update from new owner: 375whp at 1.4bar on 98, at Tokyo Motorsport

Are you sure?

0.7 bar is lot of sucking power. Whats ur expert opinion?

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MY08 STI 422whp at 1.5bar on E85, built by Diversion Garage, assembled and tuned by EvoR

Update from new owner: 375whp at 1.4bar on 98, at Tokyo Motorsport

I'm not an expert, so I go easy on giving advice like this as it might cause someone's setup to go BOOM.

Are you an expert?

Interesting. what's the internal design of the can? R head breather and crank breather separated by chamber/one way valve? If one of them has higher pressure, it could prevent the other to breathe properly, hence the oem design has them separated?

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MY08 STI 422whp at 1.5bar on E85, built by Diversion Garage, assembled and tuned by EvoR

Update from new owner: 375whp at 1.4bar on 98, at Tokyo Motorsport

No, but I am not internet warrior neither, and I genuinely want to help and learn.

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MY08 STI 422whp at 1.5bar on E85, built by Diversion Garage, assembled and tuned by EvoR

Update from new owner: 375whp at 1.4bar on 98, at Tokyo Motorsport

But you are an internet warrior! And your bad advice is going to cost someone dearly. You need to slow down on the (bad) advice you give.

Have you looked at OEM??? They join in the the same pipe back at the intake


The green line is a factory pressure equalizer as explained about in rosscos thread linked on page before



As for internal design there is a baffle plate that the oil ports are lower than and directs the oil to bottom of can then there is a filter and at the top the two air lines hook on to that would need to breathe like 1.5l of oil before it went back to motor my intake and cooler is completely oil free and has been since install 3 years ago

using the Perth-WRX mobile app

I could be completely wrong but the only way I reckon oil could get sucked backwards up from the sump is if the catch can was full and overflowing into the vacuum return line creating a siphon path while it was in vacuum.

A non return valve on the drain to sump would be piece of mind I guess.

Gordon - crude experiment but I just stuck a straw into a stubbie of beer (straw above the liquid level) and sealed the top of the bottle off with blue-tack. Was not able to suck any beer from the stubbie!!

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Bye bye betty blue. Hello F6.

Jacob, I know they r joined at the inlet pipe, but r the two nipples close to each other? In a confined space, ie catch can, air flow from the breathers can form vortex, where as in inlet, the flow from the filter is much more significant than breathers'. I said that because i had the grimspeed AOS, it joins head breather, crank breather and oil filer, as the result, it did nothing but push more oil to my tmic. The factory inlet, does have about -0.05bar pressure (vacuum), to help the ventilation. Crank and head pressure equaliser is not close to crank and head breathers, in my opinion, its not effective enough to completely compensate pressure diff. My crank breather collects more oil than my head breather.

Nick, your sump is not sealed as your bluetack test, it can let air in through inlet valve and crank breather. Why cars from cold weather need frequent oil change, the cold and moist air from surrounding environment in crankcase brings so much condensation into oil when oil start to warm up.

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MY08 STI 422whp at 1.5bar on E85, built by Diversion Garage, assembled and tuned by EvoR

Update from new owner: 375whp at 1.4bar on 98, at Tokyo Motorsport