What are the little breathers that people put on their valve covers?

[supafly1024]

I've seen people with little breathers on their valve covers and I just wanted to know what good it does to have one on there? Does anyone know, if it helps at all, is it just for looks, or does it actually hurt performance?

:huh:

[BoosterSH]

I dont know what it does, but it sits where your breather hose is. The hose attaches to your intake pipe so all its really doing its getting air from your engine rather than your intake.

To me it looks pretty cool, but i think thats about all it does.

[supafly1024]

Cool deal man, thanks for the response. It looks to me from the way the inlet is angled on the intake that it would actually create a vacum effect in the valve cover. Because of the angle of the inlet on the intake I don't see how air could flow from the intake to the valve cover. It seems to me that the air flowing by the inlet on the intake would create negative air pressure in the intake and that would actual suck air through the hose coming from the valve cover. But maybe I'm just over-analyzing everything. But if I'm right then the breather that people put on their cars would actually hurt the performance as far as that goes.

[fritz_269]

suprafly1024 - you've got it just backwards. The inlet is angled such that a little bit of clean air is rammed into that hose and into the head. From there, it flows through the head, out through the PCV valve and into the vacuum of the intake manifold.

The idea is to expel the exhaust gasses that have leaked into the head past the valve seals. Without the ventilation, the gasses will form acids in the oil.

At low throttle, the manifold vacuum is enough to pull the air through the head and PCV. But at WOT, there is no manifold vacuum and the only way air will circulate is if it is pushed through the that hose in the intake tube. If you replace this inlet hose by a breather filter, you'll be fine at low throttle, but have very little air circulation at WOT - just where you need it most!

I would not recommend a valve cover breather filter for any Honda engine. In fact, I'd recommend you modify that inlet hose to be angled even sharper into the incoming airstream to provide more air circulation at WOT - particularly if you have a high-compression or FI engine.

You will often see breathers on many domestic V8 engines - that's because they use a different route for the air - it comes up from the crankcase through the pushrod holes into the head, and then it goes OUT the breather. That is just the opposite of the Honda engine.

Upshot - don't use a breather filter on the INLET side of the head ventilation system. (Which is where every idiot I've ever seen seems to want to put them on a Honda).

[supafly1024]

Thanks a lot for that info Fritz! I definitely won't be getting one of those breathers.

[krnboy817]

ok i have a 99 prelude vtec and i have two breathers on... one is on the ram air intake pipe and other is on the cranck case opening that is facing directly towards the intake breather filter.

am i supposed to but those on the PCV connecting hose or the outlet that is connected from crankcase to the intake manifold?

[AcesHigh]

You only need one hose going from the intake pipe to the engine block. Please don't dig up a thread from the dead.