Using a breather on the head

It seems to me that if I disconnect the hose that goes from the head to my AEM CAI that I would truly be gettin cold air. Any advantages to using a breather, I know it lets out some sort of gases into the environment.

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.

Why the hell do they sell those things then! Thanks thats $20 I’m gonna save.

Originally posted by enriq415
Why the hell do they sell those things then! Thanks thats $20 I’m gonna save.

they can be put to good use on turbo’d vehicles… :slight_smile:

because they know stupid “uneducated” 2F2F ppl (not saying you) will buy it. but ur now educated and know the ill effect of this product.

A buddy of mine had one on a D16A1 motor in his 87 civic. I never really got the purpose for it. But now i know. No stupid 2f2f people think that by applying a APC sticker to your car somehow makes it Nopi Nationals material. Or that by going out and buying a cone air filter (also APC) makes like 60 hp on your car. trust me i have to put up with the 2f2f 2bull crowd everyday:mad:

keep the factory vent system…unless you know more than the Honda Engineers…

its there for a reason.

my final thoughts on the pcv system while i was answering another question and about breathers while n/a. boosted i need to rethink it all, but in the meantime the dual pcv seems best-

as far as the pcv, i guess the positive pressure description really pertains to higher throttle positions. that guy on h-t proved that at low speed the valve cover spits as well as sucks. now with such a high vacuum from the intake tube, the stock system must be sucking from the valve cover at idle. the pcv plunger is up so its sucking a little from the crankcase as well. whole lot of sucking going on there.

now at WOT, the pcv is almost closed since there is almost no vacuum. pressure from blowby pushes out the pcv and a lot out the valve cover.

in neutral, car still:
idle warm up: 0.9 psi drawn into the valve cover
idle operating temp: 0.8 psi drawn into the valve cover
2000 rpm: 0.75 psi drawn into the valve cover
5000 rpm: 0.70 psi drawn into the valve cover
8000 rpm: 0.65 psi drawn into the valve cover

under load:
Idle - 2K rpm… .75 to .8 psi vacuum into the valve cover.

whenever I place any amount of load on my car the vacuum pressure dropped down quickly.
2nd gear pull to 4K rpm the vacuum pressure quickly dropped to .5 psi vacuum drawn into the valve cover.

In 4th or 5th gear at 3-4K rpms I would quickly remove all vacuum present and noticed my needle went past 0 psi.

Out of curiousity I then reversed the vacuum ports to read any pressure comming out of the Valve cover under load.

Tests indicate that under load the pressure would shoot up to a maximum of .45 to .5 psi being pushed out of the valve cover.

Even at half throttle at 3500 rpm in 4th gear the flow reverses blowing air out of the valve cover into the intake… this is not just an issue at WOT or high speeds… This is an issue when any fair amount of load is placed on the sytem.

Under acceleration and high load situations blowby is extremely high and consequently the PCV valve/purge hose cannot supply enough vacuum to remove all the gasses needed. This is when the flow reverses from the valve cover to the intake. Their is so much blowby present that both the PCV valve/purge hose and the Valve cover breather/hose have to both vent excess pressures created. The PCV is working at its best but can’t keep up with the demanding pressures cre

soo, my take on the breather- at idle it wont be helping to suck from the valve cover and crankcase. the little vacuum at the pcv will be doing the sucking, while whatever it cant suck will be pushed out the valve cover. i guess its not too much of an issue since its only at idle. at load, it will spit out oil vapor if you have lots of blowby since the pcv isn’t enough to suck it out.

what i would do - either run a catch can before the breather (or with the breather on top), or run a catch can inline to the intake, which is what i did for a while. it barely collected any oil while n/a.

Being my car has been like this for the 2 years ive had it… will putting the hose on there help my oil burning?.. i know my valve stem seals have problems but i also kno some is going past the rings at higher rpms…

also would i just run a hose from the valve cover to the intake?.. or do i needa find all that stupid spider web lookin shit that comes on the cars originaly