oil breather

[scotts94_z28]

what exactly will an oil breather do for you and what effect if any will it have on performance. By oil breather i mean the air filter looking thing that screws into the valve covers where the oil fill hole is

[Rob B (shoebox)]

It's not going to do anything for you. When functioning properly, the closed PCV system works to relieve harmful vapors from your crankcase and burns them with the a/f mixture. Adding a breather allows a small amount of unmetered air eventually into the intake system and will cause the computer to have to compensate by virtue of what the O2 sensors see.

[Injuneer]

I agree wth Rob. No purpose at all, no performance gains with a breather. Unless you have a blower, and even then there are ways to keep the system "closed". I push 800HP with the stock PCV system fully intact. An "appearance" mod, at best.

[ryan34]

In my camaro the ventelation tube goes into the air hat, but it wouldn't stay connected. So instead of having little bits of oil and other nastiness spew onto my engine, I hooked up a breather. Seems to work fine for me, but like they said its not really for "performance".

[wolfdogs]

not for performance. but does relieve some pressure in the crankcase that was attributed to the notorious intake oil leak problem.

i ran one on my compTA with no probs and its still there with the new owner at 54k miles.

we have one on the hawk, no probs, its been there for 73k miles.

[M3EATER - GG '00 WS6 T/A]

In my camaro the ventelation tube goes into the air hat, but it wouldn't stay connected. So instead of having little bits of oil and other nastiness spew onto my engine, I hooked up a breather. Seems to work fine for me, but like they said its not really for "performance".

Ryan...

Your 91 Camaro uses a different system than the later LT1 systems. On the LT1 the crankcase is sealed up as part of the intake system and any air going through the PCV is considered "metered" air. In other words, the engine management system is accounting for it and proper fuel is being metered along with that air flow (or lack of it).

Your 91 system is, in effect, vented to the atmosphere (just as if it had a breater on the valve cover) as far as the engine management is concerned. The fact that the hose actually goes into the air filter box (or any point before the air flow meter) is for emissions purposes so that it isn't actually venting to the open air, but is being drawn back through the intake.

Gordon

[Rob B (shoebox)]

On a N/A car, I really don't see how adding a breather gets rid of more pressure in the crankcase. On the LT1, fresh air is being pulled IN from the throttle body through the hose to the valve cover. That air is being pulled in by virtue of the vacuum of the PCV system. So, you are still getting fresh air, just by another source.

[M3EATER - GG '00 WS6 T/A]

In very lay terms......

There is no need for 'fresh" air in the crank case. The PCV is used to relieve the pressures that are built up in the crank case as the volume of the crank case changes as the pistons go up & down ... and the small amount of compression pressure in the cylinders is forced past the pistons (blow-by) into the crank case.

A vented crank case (the old vented valve cover caps) just opens the crank case to the atmosphere and the pressures are equalized. The crank pressure is relieved to the atmosphere ... along with the emmissions vapors.

Next step was to have a nipple and hose on the cap and run it into the air cleaner (filter box) for the vapors to be drawn in along with the intake air, so that it wasn't just venting to the atmosphere.

The advent of PCV systems was a first shot at keeping these emissions vapors from going directly to the atmosphere and actually controlling them. The crank case is vented into the intake manifold (or the base of the carb) and is subject to intake vacuum. Hence, actually scavenging the crankcase pressure and vapors (to a small degree).

You ever see the hoses going from the valve covers to the header collectors on a drag race engine? This is a crank case evacuation system. The hoses are connected to a one way check valve that is inserted into the collector on an angle so that at high RPM the exhaust gas passing the end of the valve creats a high vacuum in the line .... and "sucks" the crank case. This system doesn't work well on a street car because it needs high exhaust gas velocity to create the vacuum. No emmissions concerns here.... just trying to keep the crank case a zero or negative pressure.

I actually used a home made crank case evac system on my old big-blocks. I had a cap on each valve cover with a hose nipple and both of them T-ed into a fitting on the intake manifold.

Today's engines are totally sealed. There is to be no venting of crank case vapors to the atmosphere ... in any way. Hence the crank case is an integral part of the intake system and the "PCV" sytem is considered metered air. Opening the system by adding a vented valve cover cap actually throws off the metering ..... as Rob noted, the engine management will work on covering up the "vacuum leak"..... as it's designed to do as small leaks occur with age ........ up to a point. When adding a vented cap..... you're actually reducing the "Positive" crank case ventilation (PCV).

Shoot..... an EFI BMW will hardly run if you leave off the oil cap .... or don't have the dip-stick all the way in.

Gordon

[wolfdogs]

In very lay terms......

Shoot..... an EFI BMW will hardly run if you leave off the oil cap .... or don't have the dip-stick all the way in.

Gordon

bavarian manuer wagaons hardly run anyway..................

[wolfdogs]

"There is no need for 'fresh" air in the crank case"


what makes you think its fresh wihen running a valve cover breather? it aint fresh.....the air goes out the breather

[M3EATER - GG '00 WS6 T/A]

.....You sure your dip-stick's all the way in, Ken......????

[Injuneer]

There is no pressure in the crankcase, when the PCV is functioning correctly - assuming you don't have massive amounts of blowby from worn rings.

The PCV valve is simply a metering device that allows a controlled amount of air/vapor to be pulled out of the crankcase by intake manifold vacuum. Pressure should never build up. It will normally be under a very slight vacuum.

The LT1 crankcase vent system is specifically designed to provide a flow of filtered, and MAF measured FRESH air to the crankcase. This FRESH air sweeps the crankcase vapors out of the crankcase and lifter valley. It needs FRESH air to dilute and sweep the water vapor that is present in the crankcase. Remember, crankcase vapor includes combustion products, and that means water vapor. If this vapor condenses in the crankcase, you will get some uglies in the oil, including acids.

The LT1 vent line from the TB to the rocker cover is also designed to function PRIMARILY as an air supply line. It takes the air from a small port, between the throttle body bores, and in front of the bores, so there is normally a very limited vacuum in this area... with a clean air filter the pressure should be very close to atmospheric.

There is a SECONDARY purpose to the vent line. IF you get excessive blowby, or you have a plugged PCV valve, the vapor buildup will cause the flow in the air supply line to reverse direction, and flow out of the vlave cover to the throttle body. This is when you start getting entrained oil in the vent flow, and it starts to build up in the top of the TB, and gets carried over into the throttle bores, coating the bores and the intake manifold with carbon. It should not be possible to build up significant pressure under these conditions.

The breather is no big deal, one way or another. If you like the way it looks, or if you get a good feeling from it, go for it - will not hurt anything. But don't atribute any magical results to it.

[wolfdogs]

.....You sure your dip-stick's all the way in, Ken......????

jus funnin wit ya man

[wolfdogs]

"The breather is no big deal, one way or another. If you like the way it looks, or if you get a good feeling from it, go for it - will not hurt anything. But don't atribute any magical results to it.'


my airconditioner car temperature dropped 20 degrees after install, and the monsoon wattage went up 34 amps! so there!!!!!!!!!

[M3EATER - GG '00 WS6 T/A]

Can always count on Fred.... thank you!