chat about PCV systems

[archemitis]

i've built and ridden motorcycles for years and the common practice is to vent your crank case to atmosphere with a small filter on the end. since its cool for motorcycles, i've been doing it on subarus for years. I put a t between the rocker covers and vent it near the firewall.

now most of my motors have blowby and venting leads to oily/gasy smells in the cab, so now im trying to figure out if a pcv valve will help me out, or do i just run the hose back further.. how bout one valve on each valve cover like V8s?

so is the idea to use manifold vac to suck gasses out of the crank case, and to suck fresh air into the crank?

every subaru i've had gets white milky mixture of water/oil in the hoses, wont this just puke into my intake, and slither down my carburetor?

 

im kindof looking for a discussion of why/if you need them, or if its more for the emissions, and not so much performance....

im not looking for answers like "just do what the engineers that designed it say"

[mcbrat]

i've built and ridden motorcycles for years and the common practice is to vent your crank case to atmosphere with a small filter on the end. since its cool for motorcycles, i've been doing it on subarus for years. I put a t between the rocker covers and vent it near the firewall.

now most of my motors have blowby and venting leads to oily/gasy smells in the cab, so now im trying to figure out if a pcv valve will help me out, or do i just run the hose back further.. how bout one valve on each valve cover like V8s?

so is the idea to use manifold vac to suck gasses out of the crank case, and to suck fresh air into the crank?

every subaru i've had gets white milky mixture of water/oil in the hoses, wont this just puke into my intake, and slither down my carburetor?

 

im kindof looking for a discussion of why/if you need them, or if its more for the emissions, and not so much performance....

im not looking for answers like "just do what the engineers that designed it say"

 

If you look at the custom valve covers for the airplane ea81s delete it totally... though I know first hand, if you do have blow by, and have it capped off (don't either vent to atmosphere, or route back into intake), you will generate too much pressure from the blow by, and start spewing oil out the seals...

 

in Missouri, it's an inspection thing. they can't be vented to atmosphere.

[archemitis]

ya, i was looking at those, im guessing they drill into the crank and vent it directly, high rpm=blowby no matter how "seated" the rings are.

 

also, i was thinking about my old chevy, it had a vent to atmosphere, with a metal tube hanging under the car to make a venturi(?), to suck the gases out at highway speeds...

[The Beast I Drive]

I ran the hose from the driver side on my ea82 strait to the intake manifold, and the one from the passenger side to the air cleaner, and I didn't use any valve, but it seemed to work

 

 

[Loyale 2.7 Turbo]

Oops! ... Double Post... See the Next:

[Loyale 2.7 Turbo]

Well... I have a Different Setup on my White Wagon (The Weberized one): first, I Joined both sides Vents to a Tee, then the open end is connected to the Air Filter`s Box.

 

The PCV has its very own ait Filter. it is a 5/8º air filter for... Cherokee? ... I`m not Sure.

 

See this Pics for More Info:

 

 

This is a Detailed view of the PCV`s Filter:

 

 

I Hope this Idea can Help you.

 

Good Luck!

[GeneralDisorder]

Well - besides cutting down on the "smelliness" of your vehicle, using the PCV keeps out water while fording if you are into off-road. That's my main purpose in using them.

 

Also, on a daily driver there's another concern - that of acidic gases forming inside the crankcase (blowby). Engine vacuum helps to pull them out of the crankcase using the PCV valve as a one-way check. Before PCV valves there was the "road draft" system that used passing air over a tube extended below the vehicle to pull the gasses out. This of course didn't fly with the bunny-huggers so the PCV system was created to burn the gases rather than just vent them.

 

On a race engine, or other limited use application where the oil is changed often this isn't an issue. Thus you see the fancy chrome valve cover breather filters.

 

Personally all my rigs run PCV - both because I don't want to have to change the oil often enough to prevent acid build up, and because I like to steam clean my engines - even the ones that don't go fording. So the benefits far outweight the 5 HP I would get from bling valve cover filters.

 

GD

[kingbobdole]

I agree with GD...

When I removed my system it was just a PITA... just keep it... and maintain your intake system by cleaning it.

[4WDFrenzy]

Yeah, I agree with both GD and kingbobdole. I currently have a breather that both fresh air inlet PCV hoses from the heads hook to. I am going to do away with it and re-route it back into the piping before the turbocharger, but well after the MAF on my wagon along with an oil catch can. There really isn't a benefit to venting the crankcase fumes to the atmosphere. If it becomes that much of a problem, get a oil catch can and plumb it in. That is probably the best plan of action.

[subaruguru]

on tiny (ea82) im just gonna run it in a U shape so it comes up and bends and gose down so the hose faces the ground. i might put a valv in both sides but thats about it. also tiny is an off road car.

[Andy FitzGibbon]

Hooking both valve covers up to a single hose defeats the purpose of the PCV system. The intent is for clean air to be drawn into the passenger side valve cover and head. The air mixes with blow by gasses as it travels across the crank case, then exits through the driver's side head and is routed back into the engine. In conditions of high manifold vaccum, the PCV valve is held open by vaccum and the air/blowby mixture is pulled into the intake manifold for recombustion. When manifold vaccum is low (such as a wide open throttle condition), the PCV valve closes and the air/blowby mixture is routed into the intake duct (SPFI) or air cleaner (carb) for recombustion.

There really isn't any reason to eliminate the system. The only reason I can think of is that if your engine has extremely worn rings, the system usually won't function properly due to high crankcase pressure. The whole system becomes a crankcase vent, rather than a "flow-through" system as the manufacturer intended, and you end up with lots of oily blow by in your intake duct (or air cleaner on carbed models). The same symptoms will occur on an unworn engine if the PCV valve is stuck or broken- blow by will be routed to the air cleaner/intake tube at all times and will leave an oily mess.

The old time trick for worn out engines is the way the old cars did it, with the "venturi tube" mentioned above (although the venturi effect isn't really necessary with the excess crankcase pressure of a worn engine). The "environmentally conscious" method is to vent the valve covers directly into a plastic bottle, which you occasionally empty.

As GD mentioned, having a properly functioning PCV system helps keep the oil cleaner by removing acidic gases from the crankcase. This won't happen if you put a little filter on each valve cover or run both valve covers into a single hose, and will only happen to a certain extent if you run venturi tubes.

Andy

[daeron]

this thread rocks, and I thought it would be a bunch of blah blah when I first saw the subject line.

 

The shadetree mechanic/engineer's "education" has lots of little gaps in it. One just got filled

 

Thanks!