saw this over at ti
the only issue is, with honda motors, putting breather valves on increases the chance of oil leaks, however the increase in H.P. at high R.P.M.'s make it all worth while to me.
i know its been beaten to death and ive read the diagrams, but why would he say that. im still not 100% clear on this
Cuz he’s a moron.
With blowby, you lose hp. 
what a crappy forum. you have to register just to read a thread. screw that. and whoever said that crap about the breather valve is talking out his ass.
Correct me if I’m wrong guys, but here is my take on this:
Notice that a long hose from the valve cover to the air intake tube? I’m assuming this is what you’re talking about. Well that long hose transfers hot gasses built-up in the valve cover back into the intake manifold for re-combustion. Allowing the hot gasses to just vent outside the engine rather recirculating it back into the intake allows the intake system to draw more outside air (that could possibly be more colder). Hence more power.
Again, I could be wrong.
Oz
Originally posted by The_Oz
[B]Correct me if I’m wrong guys, but here is my take on this:
Notice that a long hose from the valve cover to the air intake tube? I’m assuming this is what you’re talking about. Well that long hose transfers hot gasses built-up in the valve cover back into the intake manifold for re-combustion. Allowing the hot gasses to just vent outside the engine rather recirculating it back into the intake allows the intake system to draw more outside air (that could possibly be more colder). Hence more power.
Again, I could be wrong.
Oz [/B]
Makes sense, but that little hose is pretty small. I doubt that much hot air can come in through there. I dunno though… 
Tuan’s article on breathers and catch cans…
The culprit in question:
Now you’ve heard the reason to get these right. lets your engine breathe better, less oil vapour from crankcase into the intake so your intake charge has less contamination and less risk for detonation.
let’s clear up the facts shall we?
from your Helms or Acura service manual
this is where this is all happening
Now this is the diagram to pay attention to from Honda
On the right is a blown up oversized disproportionate version of your stock intake for clarity. On the left is a cross sectional view of your engine.
Start on the left at the crankcase. Note that your crankcase vapours including blow-by travels (black arrow) up the breather chamber to the PCV valve and then back to the cylinder head intake side.
Fresh air (white arrow) travels down the TB and after the TB can take 2 paths: 1) to your intake manifold and then cylinder head where it dilutes the crankcase vapours and 2) to the intake breather hose to the valve cover and then down directly to the crankcase to feed it fresh air.
So, this debunks a lot of misconceptions:
If you disconnect the valve cover breather and slap on a k&n filter what happens?
Your crankcase loses its source of fresh air to replenish it. The crankcase loses its vacuum and the ring seals don’t seal properly. You get even more blow-by. A vicious cycle starts where less and less fresh air is being delivered to the crankcase and more blow-by occurs. Less compression means less power boys.
Secondly, the valve cover breather has nothing to do with the oil crankcase vapour route. It does not prevent the oil crankcase vapours from going into the cylinder head. What it does do is reduce the amount of fresh air going to the valve cover and then the crankcase such that more air is delivered to the cylider head to dilute the crankcase vapour and more fresh air intake charge.
To prevent the oil vapour from going into the cylinder head you need an oil catch can (Moroso, Cusco, Greddy, Summit) placed at the PCV valve and hose to filter out the oil.
We can discuss oil catch cans, oil intercoolers, and remore oil filters in another segment later.
So, would I put a k&n breather filter on and disconnect the valve cover breather hose from my intake ? No. It’s like making your engine crankcase breathe by exhaling only. I can guarantee you will fail emissions with this puppy too.
Thank you Sir rev alot for posting that I hate to see people ruin their motors using those stupid breathers.
XDEep just so you know Tuan is Michael Delaney on Team Interga.
Exhale only? If the crankcase wants air then the mini filter will allow it to suck air in, its not going to cave in is it, thats my understanding…
also it eliminates one potential source of hot air going to the intake… might not be much but hey, ever bit counts in the race for hp 
Sir rev alot thanks for explaining it better.
Originally posted by Sir rev alot
[B]Your crankcase loses its source of fresh air to replenish it. The crankcase loses its vacuum and the ring seals don’t seal properly. You get even more blow-by.
why is there less compression? is it cuz there is no backpressure on the compression stroke during valve overlap (if any with stock cams)? im still trying to visualize the vacuum it needs vs the vacuum the intake creates.
if gases are exhausted, air is naturally displaced so wouldnt it be more free flowing? i guess i need to better understand ‘backpressure’ and why you lose low end with a free flowing exhaust/open header
Backpressure: The myth and why it’s wrong.
I. Introduction
One of the most misunderstood concepts in exhaust theory is backpressure. People love to talk about backpressure on message boards with no real understanding of what it is and what it’s consequences are. I’m sure many of you have heard or read the phrase “Hondas need backpressure” when discussing exhaust upgrades. That phrase is in fact completely inaccurate and a wholly misguided notion.
II. Some basic exhaust theory
Your exhaust system is designed to evacuate gases from the combustion chamber quickly and efficently. Exhaust gases are not produced in a smooth stream; exhaust gases originate in pulses. A 4 cylinder motor will have 4 distinct pulses per complete engine cycle, a 6 cylinder has 6 pules and so on. The more pulses that are produced, the more continuous the exhaust flow. Backpressure can be loosely defined as the resistance to positive flow - in this case, the resistance to positive flow of the exhaust stream.
III. Backpressure and velocity
Some people operate under the misguided notion that wider pipes are more effective at clearing the combustion chamber than narrower pipes. It’s not hard to see how this misconception is appealing - wider pipes have the capability to flow more than narrower pipes. So if they have the ability to flow more, why isn’t “wider is better” a good rule of thumb for exhaust upgrading? In a word - VELOCITY. I’m sure that all of you have at one time used a garden hose w/o a spray nozzle on it. If you let the water just run unrestricted out of the house it flows at a rather slow rate. However, if you take your finger and cover part of the opening, the water will flow out at a much much faster rate.
The astute exhaust designer knows that you must balance flow capacity with velocity. You want the exhaust gases to exit the chamber and speed along at the highest velocity possible - you want a FAST exhaust stream. If you have two exhaust pulses of equal volume, one in a 2" pipe and one in a 3" pipe, the pulse in the 2" pipe will be traveling considerably FASTER than the pulse in the 3" pipe. While it is true that the narrower the pipe, the higher the velocity of the exiting gases, you want make sure the pipe is wide enough so that there is as little backpressure as possible while maintaining suitable exhaust gas velocity. Backpressure in it’s most extreme form can lead to reversion of the exhaust stream - that is to say the exhaust flows backwards, which is not good. The trick is to have a pipe that that is as narrow as possible while having as close to zero backpressure as possible at the RPM range you want your power band to be located at. Exhaust pipe diameters are best suited to a particular RPM range. A smaller pipe diameter will produce higher exhaust velocities at a lower RPM but create unacceptably high amounts of backpressure at high rpm. Thus if your powerband is located 2-3000 RPM you’d want a narrower pipe than if your powerband is located at 8-9000RPM.
Many engineers try to work around the RPM specific nature of pipe diameters by using setups that are capable of creating a similar effect as a change in pipe diameter on the fly. The most advanced is Ferrari’s which consists of two exhaust paths after the header - at low RPM only one path is open to maintain exhaust velocity, but as RPM climbs and exhaust volume increases, the second path is opened to curb backpressure - since there is greater exhaust volume there is no loss in flow velocity. BMW and Nissan use a simpler and less effective method - there is a single exhaust path to the muffler; the muffler has two paths; one path is closed at low RPM but both are open at high RPM.
IV. So how did this myth come to be?
I often wonder how the myth “Hondas need backpressure” came to be. Mostly I believe it is a misunderstanding of what is going on with the exhaust stream as pipe diameters change. For instance, someone with a civic decides he’s going to uprade his exhaust with a 3" diameter piping. Once it’s installed the owner notices that he seems to have lost a good bit of power throughout the powerband. He makes the connections in the following manner: “My wider exhaust eliminated all backpressure but I lost power, therefore the motor must need some backpressure in order to make power.” What he did not realize is that he killed off all his flow velocity by using such a ridiculously wide pipe. It would have been possible for him to achieve close to zero backpressure with a much narrower pipe - in that way he would not have lost all his flow velocity.
V. So why is exhaust velocity so important?
The faster an exhaust pulse moves, the better it can scavenge out all of the spent gasses during valve overlap. The guiding principles of exhaust pulse scavenging are a bit beyond the scope of this doc but the general idea is a fast moving pulse creates a low pressure area behind it. This low pressure area acts as a vacuum and draws along the air behind it. A similar example would be a vehicle traveling at a high rate of speed on a dusty road. There is a low pressure area immediately behind the moving vehicle - dust particles get sucked into this low pressure area causing it to collect on the back of the vehicle. This effect is most noticeable on vans and hatchbacks which tend to create large trailing low pressure areas - giving rise to the numerous “wash me please” messages written in the thickly collected dust on the rear door(s).
VI. Conclusion.
SO it turns out that Hondas don’t need backpressure, they need as high a flow velocity as possible with as little backpressure as possible.
so is the velocity through a stock pipe actually faster than if its immediately evacuated into the atmophere like running an open header?
if its all about velocity, how come when you have a straight through muffler with the inner tube the same size as the rest of the exhaust system, you still lose low end? is it possible to still retain the stock low end while having a more free flowing exhaust? or is this why we haev vtec…
also why dont people just make a shorter pipe… like sticking out hte side or something heh
When you race you really don’t need “low end”, hell my low end is gutted but my LS can still hit a 14.9.
ARCHIVETHIS
Imagine this…
So you have got an intake, exhaust and headers…You have just gotten the engine’s output increased. Your combustion pressures are higher and are enhancing the piston in traveling downwards hence improving power.
But what if you could add a little bit of assist in some way or another…
What if you could take vacuum and apply it to the bottom of the piston…
This will create a greater pressure difference for the piston. It will create more power, low end torque, improve on emmisions, and prolong piston ring life…and end result will be a longer life engine.
Intake manifold gets its vacuum in pulses. And that is how the breather hose is capable of supplying the vacuum to your crankcase. So that ten dollar breather just got your whole PCV system bypassed and is costing you considerably more in the long run…
Greddy’s catch can will be the perfect replacement for the factory hose. It will keep the system functional and will reduce the chance of oil getting in the manifold and ending up as carbon buildup.
Originally posted by carchitect
[B]Imagine this…
So you have got an intake, exhaust and headers…You have just gotten the engine’s output increased. Your combustion pressures are higher and are enhancing the piston in traveling downwards hence improving power.
But what if you could add a little bit of assist in some way or another…
What if you could take vacuum and apply it to the bottom of the piston…
This will create a greater pressure difference for the piston. It will create more power, low end torque, improve on emmisions, and prolong piston ring life…and end result will be a longer life engine.
[/B]
What are your plans for lubricating this system? The vacuum would suck all the oil out of the cylinders.
Sir rev alot: Good job explaining this stuff 
This topic has been beat dead before:
http://www.g2ic.com/forums/showthread.php?s=&threadid=13155&highlight=catch+can+pcv
http://www.g2ic.com/forums/showthread.php?s=&threadid=13322&highlight=catch+can+pcv
http://www.g2ic.com/forums/showthread.php?s=&threadid=16062
I REMEMBER YOU FROM MODACAR!!! I had the black G2 with the CF hood and the JG head… ghetto blue intake and stock header. A lot has changed since…
I get what you are saying, that the breather hose helps to “suck the piston down” thereby increasing power. I don’t see how that little tiny hose can make any noticable difference in power though. Maybe one tenth of a horse power?
How did exhaust velocity get thrown into this topic?
two kills with one thread.
" What are your plans for lubricating this system? The vacuum would suck all the oil out of the cylinders."
If you are so concerned about vacuum, then at idle the vacuum will cause your engine to be a real smoker by pulling oil into the combustion chamber thru the piston ring gaps. Oil is very slow at moving within an engine. It relies on pressure to motivate it. Its still very slow in comparison to the speed of the reciprocating parts within. Oil is used only as a surface lubricant on all load bearing items, such as rocker arms, cylinder walls, piston pins, rod, main and thrust bearings, etc…
Now don’t read on unless you want to realize what you are doing to the enviroment…
Before the 60s there were no emmisions standards. Now we have a lot of standards. I think it maybe a little too much for our passenger vehicles. The f_cking SUV and full size trucks have a lower standard to pass. Which means they can enter what they call a LEV or low emmision vehicle just for matching the emmisions requirements for a standard passenger vehicle. The really worst part is that diesel trucks and 18-wheelers have absolutely NO standards of emmisions. And since those atmosphere polutants are not only creating emmisions that our passenger cars are supposed to cleanup they are also tearing up our roads. When the government realizes that the emmisions are too high in a particular city, like dallas/fort worth or houston, they clamp down the monetary expenses for the street improvement and highway funding. Which makes it harded for us taxpayers to enjoy our nice vehicles without getting some sort of damage due to improperly paved roads.
Most rigs out there will not pass their safety inspections. They some how get around that. The industry is so large and has such a strong and corrupt hold on the government that we the innocent by-standards ,which means you and me, pay the price in the long run.
I ride a sport bike often and one of the most life threatening occurences of my life happened on me one day. I was wanting to take it for a spin after three weeks of rain. So one sunny sunday I took it out of a spin. I filled her up and hit the high way to head for a remote road I know that lets me hit the apex like a razor. As soon as I had gotten on the highway, my intentions were to get in the lane you get noticed and have the least amount of vehicles, the left lane. I switched from the right to the middle then when I looked back in my blind spot to switch over to the left lane I had gotten greeted by a torn off re-tread of a rig. It wrapped one end around the armpit and smacked my helmet with the other end. The instant this hit me I had to let go of the handle bars to get it of me. But the instant I did the quick weight shift and the shock to me and the bike put it into a tank slapper. I though I saw life flash before my eyes. I recovered it by luck or who knows what. And i’m very fortunate that I had my leathers and helmet on. I still got brused below the jacket. and my gear which I paid a pretty price for is now tornup.
If passenger cars require emmisions than so should rigs.
If passenger cars can’t wear re-treads than so shouldn’t rigs.
If passenger cars can’t be on the road without passing their state inspections then so shouldn’t rigs.
So if you care to remove your emmisions controlling items your car came with then:
Who will clean up the atmosphere?
How are the streets going to be maintained without any funding?
How will we drive our cars when gasoline usage gets a ban by the government due to polutants?
How are you going to expain to your little ones that why you have two hands and two legs while they have 4 and one of which doesn’t even function ?
You get my point don’t you? I would rather have a stock car still moving me from point a to b then have a nice modified car and still have to take the bycycle to work 30 miles because the gas price is 15.99 a gallon!!