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The breather helps ventilate the crankcase. It surprises me how many people mistakenly think the air blows out into the intake so they think removing it will give them more power. Talk about misinformed. Mike D posted a good write up on this before:


Here's the stock PCV diagram from the Helms manual. on the left is a cutaway view of the engine. on the right is a cutaway view of the stock intake. In the middle are the separate breather circuit and the PCV valve circuit:



all you have to learn is how the fresh air cicuit flows (follow the open white arrow) and how the crankcase vapor (with oil vapors in it ) circuit flows (follow the black arrows). Notice which circuit flows to the valve cover (on top of the engine on the left)....it's NOT the crankcase vapors. When you add a breather, you remove the line from the intake to the valve cover.


The honda crankcase breather is a POSITIVE pressure ventilation system.The air from the intake blows into the valve cover. It is NOT a negative pressure ventilation system...it does NOT suck air from the valvecover to the intake.

Breathers remove the source of positive ventilation that repressurizes the POSTIVE CRANKCASE VENTILATIoN (PCV) valve.

There is less pressure in the crank when you add a breather at the valve cover. The consequence of this is you get more positive blow-by from the combustion chamber past the piston rings and into the crankcase. More blow-by means less cylinder pressure...less cylinder pressure means the burn is slower and less complete...the result is more emissions and less power.

If you want to do this right and remove oil vapor from the circulating crankcase before it goes into the intake valve then, get an oilcatch can and put a breather on the catch can. Then place the catch can in between the valve cover breather and the PCV valve.

Disconnecting the breather tube, which blows fresh intake air into the valve cover, and placing a breather on the valve cover just creates more blow-by and emissions. Eventually you have so much blow-by, you lose power.
 

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I honestly don't know what the whole reason behind the breather filters are. Without the intake helping to create the possitive pressure the engine won't suck in any fresh air and the crankcase will not be ventilated correctly. But seeing them at an autoparts store in a little bucket labeled $3.99 was a good sign to me that they were useless.

I think Endyn's breather kit (with oil catch can) has some sort of configuration for turbo setups, I'm not sure.
 

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kelly on Dec/04/02 said:
Under WOT throttle the air comes out of the valve cover because the throttle is wide open and the intake tube and intake manifold are at the same pressure. The PCV opening at the intake tube opening could even be at lower pressure under these circumstances due to the venturi effect.
I've never had a zero or positive reading on intake manifold pressure. The ECU still reads a slight negative pressure at WOT. It might not be strong enough negative pressure to continue to draw air in through the PCV but I certainly don't think it would be blowing out.
 
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