Breather Hose

I was wondering what the purpose if a breather element would be on the valve cover. I have heard stories that by eliminating the breather line to the intake that it saves oil and by sealing up the hole in the intake would allow more vacuum for air to enter. I know that the line is there for a reason and thats why all After Market intakes include a bung and a line for it but what is its true purpose?

please search.

heres a 6 page thread about it over at you have to register before reading, but worth it. i’ll copy and paste specific important parts from the thread.

"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:

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.

from the tuan(michael delaney):
"you have to remember that oil vapor into the IM cannot be helping your cause. The oil vapor occupies space or volume. That means less air/fuel mix going in wuth one gulp of the intake valve opening.

The thought behind the breather is that you are supposed to get more fresh air flow down into the crankcase from the valve cover. This increases the cycle of oil vapor flow out of the crankcase. The added fresh air displaces the oil vapors in the crankcase with the assistance from the IM vacuum sucking it out. You evacuate the crankcase more effectively…or so the thought behind it goes. Remember you have converted a closed system into an opeb PCV system when you add one of those breathers.

We have a PCV system designed as a closed system though. When attached to the intake, the breather hose actually generates more pressure gradient to push fresh air down into the crankcase via the valve cover breather from the intake at higher engine speeds! When you use only 1 breather in an open system, not enough fresh air coming through the breather filter gets down to the crankcase.

The crankcase has less pressure inside. This opens the door for more blow-by. Without the positive pressure in the crankcase to offer some resistance to blow-by past the piston ring, you get crap going down. The other problem with less fresh air entering is, as was said before, the circulation flow out to the PCV valve is decreased. So more crap stays in the crankcase. It becomes a vicious cycle.

If you insist on using an open PCV system then drill a second hole and mount a second breather tube in the valvecover. Using 2 breather filters will deliver enough fresh air down to the crankcase.

Now the other smart move would be to use an oil catch can that is baffled so that it captures or intercepts the oil in the vapor leaving the crankcase before it reached the PCV valve and enters the IM. Now you have more fresh air entering the IM instead of oil vapor.

If you plan to use an open system, add more breathers. If you use a closed system or an open system, use an oil catch can.

The good oil catch cans have baffles and drain the captured oil back to the oil pan without you having to empty them periodically.