Venting PCV and Oil contamination.

Messages
39,806
Location
Pottstown, PA
Quote:
Most autos with mufflers according to some people on Honda-Tech have reported positive or almost no negative pressure on the slash cut.
If they've got flow with a velocity, with a venturi tap (the extractor) installed, it will draw a vacuum. These were OEM on 80's GM's grin Grumpy Jenkins pioneered them in racing. GM liked it so much, the adopted it until the EPA wanted all crankcase emissions to pass through the combustion chamber before hitting the catalyst.
Quote:
Most engine have leaky seals, thus no matter what you read on the web, you will never achieve negative vacuum in the crankcase,
Oh, really? I guess when I merely installed the hose to the extractor on the normal fresh air connection on the valve cover since my PCV was one of those dinky poppet deals tapped to one intake runner on my Mitsubishi 3.0 ...the seal just coincidentally let go a short time later. My crank pulley doesn't believe you. This is not something I've pulled out of my behind LOL
Quote:
have you tried sucking on those valves?
While not something I'd normally do, which one(s) are you talking about? The anti-back fire valves? They're check valves. Are you sure you had them forward biased in the suction test??
Quote:
plus when the opposing side of the PCV system is a 5/8ths tube with no restriction.
Here you lost me. You stated that your catch can caused too much restriction. I merely offered an alternative to the catch can in the form of MUCH BIGGER hoses. You have NO VELOCITY ..hence anything that's heavy will drop out. The lighter vapor will not be inhibited. Naturally you would want it laid out in a manner where it would drain back after the severe event.
 
Messages
193
Location
MN
Thread starter
Originally Posted By: Gary Allan
Quote:
Most autos with mufflers according to some people on Honda-Tech have reported positive or almost no negative pressure on the slash cut.
If they've got flow with a velocity, with a venturi tap (the extractor) installed, it will draw a vacuum. These were OEM on 80's GM's grin Grumpy Jenkins pioneered them in racing. GM liked it so much, the adopted it until the EPA wanted all crankcase emissions to pass through the combustion chamber before hitting the catalyst.
Quote:
Most engine have leaky seals, thus no matter what you read on the web, you will never achieve negative vacuum in the crankcase,
Oh, really? I guess when I merely installed the hose to the extractor on the normal fresh air vent since my PCV was one of those dinky poppet deals tapped to one intake runner on my Mitsubishi 3.0 ...the seal just coincidentally let go a short time later. My crank pulley doesn't believe you. This is not something I've pulled out of my behind LOL
Quote:
have you tried sucking on those valves?
While not something I'd normally do, which one(s) are you talking about? The anti-back fire valves? They're check valves. Are you sure you had them forward biased in the suction test??
Quote:
plus when the opposing side of the PCV system is a 5/8ths tube with no restriction.
Here you lost me. You stated that your catch can caused too much restriction. I merely offered an alternative to the catch can in the form of MUCH BIGGER hoses. You have NO VELOCITY ..hence anything that's heavy will drop out. The lighter vapor will not be inhibited. Naturally you would want it laid out in a manner where it would drain back after the severe event.
Well maybe you can further elaborate on your experiences. The Catch can required about 4ft of extra 3/8ths hose to mount it, This also was routed to a vacuum block. The restriction was durring heavy loads. The valve im talking about is the PCV valve. Clearly i knew the flow direction ive installed hundreds. If you blow through it there is quite the restriction. My guess is to reduce oil vapors from getting into the intake manifold and control a pretuned vacuum leak. Let me rephrase this. Alot of engines ive personally have worked on have had something as small as a valve cover gasket leak somewhere, or even a small rear main seal leak, which lets air in. And I cant see how that could assist negative vacuum inside the crankcase when there is no opposite restriction. And gary I would love to install one of those slash cuts in the exhaust, however I do not have easy access to a welder at the moment.
 
Last edited:
Messages
39,806
Location
Pottstown, PA
You're confusing me with the term "opposite restriction". Do you mean an uninhibited fresh air intake? The PCV valve is a choke point at some point in positive crankcase pressure. Sure. The goal of everyone I know that has this issue is to control either the consumption or the oil soaking the upper side of the throttle body. Ideally both. If we can agree on that ...then it merely means you need to revert the heavily oil soaked high velocity vapor to a low(er) velocity vapor where it can no longer suspend the oil droplets. This you do with either a large chamber (the catch can - works just like a shop vac in reverse) or just enlarge or lengthen the hoses. Preferably both.
 
Messages
193
Location
MN
Thread starter
^^^while retaining the closed loop form I would assume? When I say opposite restriction, I mean the 2 sides of the PCV system. PCV - crankcase side, and the Valvecover to intake hose/TB side. Durring normal idle, cruise and decel, the PCV valve is open and the negative vacuum in the IM pulls pressure from the PCV valve. The air is replaced with fresh air from the Valve cover to Intake/TB side. The nissan has an orifice to reduce flow on the Valve cover side, to help create a negative pressure inside the engine durring cruise, to assist with vapor evac. This is the opposite restriction im talking about. This is the restrictor, its a 5/8ths fitting, with a about barely a 1/4th hole drilled in the middle. If the PCV valve is pulling a small amount of vacuum, but there is no restriction on the opposing end, there is almost no volume of air moving correct? This is what my understanding for nissan installing a restrictor on the intake/TB, and what other nissan enthusiasts have reported.
 
Last edited:
Messages
782
Location
Philadelphia, PA
Have you ever considered hooking up an air/oil separator in line before the valve, or is this what you mean by "catch can"? Lots of guys have done it on a Ford Explorer forum I frequent with great success. I can try and find some threads on it if you'd like.
 
Messages
39,806
Location
Pottstown, PA
Oops ..didn't catch your edit. Okay, now we're oriented to the fresh air inlet restrictor. This is the first such installation of this I've ever seen. Well, at least as shown. At idle, due to your restrictor, the PCV valve is probably open. This would be unlike most in that they're constantly cycling as they bleed off vacuum.
Quote:
If the PCV valve is pulling a small amount of vacuum, but there is no restriction on the opposing end, there is almost no volume of air moving correct?
Well, it's got less potential. At WOT, normally, it's in parallel with the air horn. It will pull a proportion of the total air flow in ratio to it's effective opening in relationship to the throttle opening. That vacuum that either sees is identical. If you didn't have the restriction ..that would be how it would normally work. Yours is opposite what most engines have. For example, instead of a bona fide PCV valve, some use a metered orifice that's installed on the IM side of the valve cover. The inlet air is unrestricted. There if the blow by exceeds the capacity of the volume being processed by through the metered orifice, the excess naturally gets vented upstream of the throttle body. That's the same result whether PCV or metered orifice. If your PCV is a legit (as in conventional) PCV, then the only thing I can think of as a result would be that the crankcase would be under almost full manifold vacuum. Some engines are designed to handle this. You can't take the dipstick out or open the oil cap without them stalling. Still, my remedy would be to lower the velocity of wherever the oil is migrating.
 
Messages
193
Location
MN
Thread starter
Originally Posted By: FusilliJerry82
Have you ever considered hooking up an air/oil separator in line before the valve, or is this what you mean by "catch can"? Lots of guys have done it on a Ford Explorer forum I frequent with great success. I can try and find some threads on it if you'd like.
Ive ran 2 of them after the catch can
 
Messages
1,877
Location
Pacnw
Originally Posted By: Bigsyke
Most autos with mufflers according to some people on Honda-Tech have reported positive or almost no negative pressure on the slash cut.
Never heard of that. Read the linked honda tech article on the bottom of first post here http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1635814&page=1. He was going for 15" Hg which is really high. He had two exhaust nipples. My VW slashcut (one exhaust nipple) is pulling from 0-3" Hg which is about what it pulls stock. It breathes better though and has noticeably more power. Of course the real benefit is there is now zero pcv gunk getting to the valves.
 
Messages
193
Location
MN
Thread starter
The catch can is under the strut tower bar. This is a setup I experimented with. I didnt like it. It felt inefficient.
 
Messages
1,877
Location
Pacnw
I would take all that stuff out of there and just run it to the exhaust and get the power gains. Or if you run to atmosphere, remove all those flow restrictions. Each of those is a flow restirciton. For a VTA (and for exhaust slashcut for that matter) you need no restrictions. It has to breathe well.
 
Last edited:
Messages
193
Location
MN
Thread starter
Thats what im going to do, however I need a bung welded for a slash cut, which wont be happening soon.
 
Messages
19,479
Location
Chicago Area
Vacuum PCV systems are more for keeping vapors and oils off of the road and out of the atmosphere. Anyone remember draft tubes and the oil line in the middle of most roads? On a side note, piston rings can be designed to utilize the negative pressure in the crankcase to work better. Seals leak less, with negative pressure. But good non pressurized venting is not necessarily bad for an engine. There is something wrong if you have to change the PCV valve so frequently. Very wrong. If your catch can is restrictive, get a bigger one or use two in parallel. If you use the common water separator type, remove the filter and run it backwards. BTW, I don't like that pictured set up, either!
 
Last edited:
Messages
1,877
Location
Pacnw
Originally Posted By: Bigsyke
And gary I would love to install one of those slash cuts in the exhaust, however I do not have easy access to a welder at the moment.
Exhaust shop will do it for $50. You have to watch to make sure they install it correctly though. As with everything an experienced muffler guy/welder makes a big diff. in installing it correctly.
 
Messages
193
Location
MN
Thread starter
So does anybody know a good method when VTA to help stop moisture and condensation from froming inside the engine? Does having the vent hoses pointing down prevent moisture from entering the crankcase?
 

mva

Messages
764
Location
Northern BC, Canada
Venting the crankcase to atmosphere is a highly polluting practice - oil fumes, small oil particles, unburnt gas, blow by exhaust straight into the air. If everyone did this picture Mexico city or LA in the early seventies - sore eyes, trouble breathing, smog, etc. PCV systems were a great innovation in pollution control, improved mileage and reduced engine wear by filtering make-up air, burning the oil droplets, burning fuel vapours and controling air circulation through the crankcase.
 
Messages
193
Location
MN
Thread starter
i dont think everyone will be doing this. They are a great innovation only for pollution control, they do not improve mileage unless replacing a clogged valve with a new one -the air is still metered from the fresh air intake, burning oil in the cylinders isnt healty, and air circulation in the crankcase only happens durring vacuum conditions such as idling or decel. On my car the pcv flows one direction, until the throttle plate is opened, then its just plain venting via positive pressure. I can contain the polution with a vented can, i just need to prevent condensation
 

mva

Messages
764
Location
Northern BC, Canada
From this link: "About 20% of the total hydrocarbon (HC) emissions produced by a vehicle are blowby emissions from gases that get past the piston rings and enter the crankcase. The higher the mileage on the engine and the greater the wear on the piston rings and cylinders, the greater the blowby into the crankcase. Before PCV was invented, blowby vapors were simply vented to the atmosphere through a "road draft tube" that ran from a vent hole in a valve cover or valley cover down toward the ground. In 1961, the first PCV systems appeared on California cars. The PCV system used intake vacuum to siphon blowby vapors back into the intake manifold. This allowed the HC to be re-burned and eliminated blowby vapors as a source of pollution" http://www.aa1car.com/library/pcv.htm By burning these hydrocarbons, rather than spewing them into the air, you will improve your gas mileage slightly.
 
Messages
1,676
Location
Waldorf, Maryland
Originally Posted By: mva
From this link: "About 20% of the total hydrocarbon (HC) emissions produced by a vehicle are blowby emissions from gases that get past the piston rings and enter the crankcase. The higher the mileage on the engine and the greater the wear on the piston rings and cylinders, the greater the blowby into the crankcase. Before PCV was invented, blowby vapors were simply vented to the atmosphere through a "road draft tube" that ran from a vent hole in a valve cover or valley cover down toward the ground. In 1961, the first PCV systems appeared on California cars. The PCV system used intake vacuum to siphon blowby vapors back into the intake manifold. This allowed the HC to be re-burned and eliminated blowby vapors as a source of pollution" http://www.aa1car.com/library/pcv.htm By burning these hydrocarbons, rather than spewing them into the air, you will improve your gas mileage slightly.
Not sure of that, have you ever looked at some of these intake manifolds? I have and they are an oily mess ! This can't be improving gas mileage. Chevy Trucks can actually use oil due to pulling vapours and oil through the PCV and burning them. Chevy came out with a small hole PCV to stop this.
 
Top