Air Oil Separator plumbing V6 Turbo

Hey all,

Long time listener, first-time caller.

I've just completed a turbo conversion of my V6 Mivec FTO and with 10:1 compression + the turbo naturally, I'm expecting plenty of blow by.

The engine has just been rebuilt and before I start to break it in I need to get my breather system set up and wanted to sense check my planned plumbing.

I have a 3-port Mishimoto air oil separator which I have planned to plumb to the intake just before the turbo.

For the 2 inlet ports, I was thinking of having one come directly from the crankcase and for the second one I would tee a line so it connects to both heads one through the OEM breather port, and for the other, I'd delete the PCV und use that.

I've attached a very rough sketch of what I'm thinking, have I missed anything?

I'm not seeing an image, but what you typed made sense. I'd just say if this is a street vehicle I don't know your local laws, but retaining PCV is suggested.

Valve cover breather ports, oil cap are sometimes options for breathing as well.

Hey Mike,

So my plan was to delete the PCV and plumb that into the air oil separator would that still work to mitigate concerns around removing the PCV.

If I retained the PCV is there any risk of keeping the OEM hose between the crank case and the PCV? I was thinking that when the car was making boost it wouldn't allow the vale to open to release that pressure build up until I had my foot off the accelerator. And may no longer actually function as intended?

With where the OEM breather hose was when the car was NA. would you suggest blanking that off/teeing it into the second inlet hose for the AOS or would I add a breather into it?

Utilizing the heavy vacuum present in the intake manifold while idling and cruising to evacuate the crankcase under those conditions still has benefits.

It may help to see an example of a system that retains PCV operation while also venting the crankcase to the pre turbo intake. If your PCV valve can't hold the boost, then replacement with a check valve that can would be required to retian PCV operation.

https://www.cobbtuning.com/products/air-oil-separators/subaru-air-oil-separator-fxt-2004-2008-wrx-2002-2007-sti-2004-2007

https://cobbtuning.atlassian.net/wiki/spaces/PRS/pages/1435893875/811615+822615+-+Air+Oil+Separator+WRX+2002+-+2014+STI+04-20

As Mike said, the PCV valve has many benefits and no real dis-advantages.

Drawing out oil fumes and moisture laden air reduces corrosion and formation of the "mayonaise" in the crankcase, and reduces fuel dilution of the oil by drawing off the boiled out lighter fuel compounds.

Here's the layout I was thinking.

How was the stock system routed Dan?

Hey Mike,

The OEM system used all 10mm hoses and the crank case breather port went directly to the PCV valve.

Thanks. Your arrangement looks reasonable for a non emissions controlled area. I don't know the rules in Ireland.

I'll just say be sure to use much much larger hoses and fittings than stock to slow the mixture down and allow for separation, reduce pressure.