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Originally posted by big eck
Good vid that and great vid. I'm thinkin on doin a track day at knockhill in November. Are the r888s really that much better in the dry than the street tyres???

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8mm bung to replace one way breather valve (that I had blocked off anyway)



cleaned and masked

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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.

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