I am trying to figure out something for my car and I have the following question. Before, I will briefly describe the routing of the breather hoses on a stock STi.

1. There are 2 breather outlets on each head. One small baffled one (A) and one large non-baffled one (B).
2. There is a crank case breather outlet on top of the block.


i. The baffled small head breather connectors get t'ed together and then routing into the intake sustem before the turbo.

ii. The crank case breather connector has a T on top of it. One end of T goes into the intake system before the turbo and another end of that T goes to the PCV valvle on the intake manifold.

iii. The large non-baffled head breather connectors are t'ed together and then routed back into the crank case through a connector on top of the block (in the rear middle part of the block).

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I do not understand the part iii. Why are the head breather routed back into the crank case? I routed mine into the oil catch tank and the tank gets filled up very very fast. So, what is the point of circulating the oil from head into the crank case via breather hoses? The oil will strain into the crank case anyways, right?

Please try to explain that to me.

- Alex

 

you got me stumped too. after that one day when we took mine apart, stared at it for 1 hour, i still dont get it. does the us sti do this also?

 

I never saw one. But I would think it has to do with the manifold being used under BOTH vacuume and pressure, depending upon the throttle position. So under 2 different conditions the crankcase needs to be exacuated.