Tucker82

iTrader: (7)

Theres a valve at the back of the inlet manifold, under the throttle body. Attached to oil breather on the cranckcase. I think its called the PVC valve???

Anyway - what does it do? Ive got an oil catch can fitted and kept it, as Ive read on here you CAN block it off!?

By blocking it off, what will affect if anything, and performance diiffrerences?

I would like to block it off TBH but not sure what im playing with..

Thanks people...

chrisdicko

iTrader: (21)

I've blocked mine off.

I cant remember where (dave_garret on here showed em it), but there was an article, and I think it was wrote by Andy Forrest, and he said in his opinion it was worth blanking it off.

Tucker82

iTrader: (7)

So you just blocked it off and nothing else? Its just if i block mine off, i want to make sure that I dont have to do anything else...

Did it make a difference in any way?

Thanks

Tucker

slipstream_uk

iTrader: (1)

From Andy's site,

"Breather system

The original PCV (Positive Crankcase Ventilation)system does indeed do some good for the engine by ensuring the corrosive gasses are removed from the crankcase and replaced by fresh filtered air.
The Subaru system has two main phases depending on manifold pressure/vacuum.
Under manifold vacuum conditions (probably 99% of the engines life) there is a non return valve under the throttle body, which allows the 'blow by' vapours to be drawn into the manifold. The vapours are replaced from the vents on the cam covers, supplied from the inlet duct. This provides the circulation of air through the engine, prevents condensation, oil contamination and internal corrosion.
This is indeed a good thing and there is a strong case to retain this system if the car is a daily driver.

Under positive manifold boost conditions, the non return valve under the throttle body closes and the hot 'blow by' gasses (Note - 'blow by' tends to be a cool vapour at low power but a hot gas at high power) are re-routed via a 't' piece to the intake duct for reconsumption by the engine. The cam cover vents may also vent out during this phase.
This is where you can get oil suspended in the gasses finding its way into the induction system......this is a bad thing ! The oil coats the intercooler, reducing efficiency and causes premature det due to lowering the octane of the fuel.

It is possible to 'catch' the suspended oil in a 'catch can' This is a reservoir deigned to reduce the velocity of the gasses, allowing the oil to fall out of suspension. The oil collects in the bottom of the can and the oil free gasses carry on to be either reconsumed by the engine or vented to atmosphere. The catch can will ideally intercept all 3 vent lines although the main culprit on the Subaru would appear to be the central crankcase vent.

The return of gasses from the catch can is also the subject of some debate. If the gasses are reintroduced to the intake system then you are asking the engine to burn an oxygen free mix ! ie you are reducing slightly the amount of oxygen fed into the engine, this can only mean less power. I personally prefer to vent to atmosphere and block off the return to the intake system. There are concerns that this is not very 'green' however the vented gasses are just of the same constitution as your exhaust gasses (assuming you have a decat exhaust)"

dave_garrett

iTrader: (24)

I think Slipstream's covered everything . You can see the PCV valve blanked of on my manifold below (you'll need a 1/4" bspt plug), you can get these from most places, I got mine for RS. I also wrapped the plug with a bit of PTFE tape for added security.

with PCV in:



with PCV inlet blacnked off (stainless plug on the right):



I choose to vent my catch can to atmosphere, others connect the vent line back to the intake (the hyperflow catch can I have has a foam filter it in to remove any suspended solids (i.e. oil/gunk). My intake pipe doesnt have any breathers on it so I had to vent to atmosphere.

You will be amazed how much gunk the catch can collects (clean mine out once a month but havent been using the car much at all recnetly)

Pic of fitted hyperflow catch can: