Is a PCV Valve Really Necessary?
Thread Starter
Melting Slicks
Joined: Nov 2000
Posts: 2,738
Likes: 53
From: Bogart GA
Is a PCV Valve Really Necessary?
I have been running one but now I am just using a vent on top of each valve cover, wouldn't this be good enough? The car is not a daily driver.
Team Owner
Joined: Jun 2000
Posts: 38,923
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From: Southbound
Cruise-In II Veteran
Your vents let the fumes out.
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
You need to run PCV system on the street for numerous reasons, the biggest being, harmful blowby vapors are replaced with fresh air. (ALL engines have some blowby).
Also, liquid moisture, which collects on components inside the crankcase upon each cool-down cycle, is vaporized (if your oil reaches 212f) then removed via the PCV system.
A pair of breathers only allow a crankcase to 'belch'. No fresh air is introduced to the crankcase. Note the term "Positive" of PCV instead of "passive".
Also, liquid moisture, which collects on components inside the crankcase upon each cool-down cycle, is vaporized (if your oil reaches 212f) then removed via the PCV system.
A pair of breathers only allow a crankcase to 'belch'. No fresh air is introduced to the crankcase. Note the term "Positive" of PCV instead of "passive".
Pro
Joined: Oct 2009
Posts: 523
Likes: 4
From: Calgary Alberta
It's is not a big deal with a non-daily driver but I would rather keep my engine compartment free of oil film which will just attract dirt and make a sticky mess over time. JMHO.
Safety Car
Joined: Oct 2004
Posts: 3,926
Likes: 739
From: Youngstown Ohio
I have a 427sb and run just vents (one on each valve cover). Mine is not driven daily, so my valve covers are mostly clean. Most (almost all) people I know with hi-po street engines (500+ hp) do not run pcv valves, just vents. Some run vacuum pumps.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
That is all I have. My problem with PCV is they don't flow at wot when you have max blow by. They screw with the A/F curve. oil mist in the intake is the cause of build up carbon on the intake valve stems restricting air flow
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
No, you don't need one, at all. You can get rid of it and just clean out your oily engine compartment once a month... 
Keeping a PCV system intact--and working--is a "no-brainer". It is virtually maintenance-free, causes no loss of performance, and eliminates the dreaded "oily engine compartment" syndrome.
What's not to like???
Keeping a PCV system intact--and working--is a "no-brainer". It is virtually maintenance-free, causes no loss of performance, and eliminates the dreaded "oily engine compartment" syndrome.
What's not to like???
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
They are tall tubes and my crane gold stud girdles might block all the rocker splash. I do refresh my motors with new rings..... every 5-10-15 thousand miles.
I never did think about oil under the hood or see much of any, maybe I am lucky.
I bought these tall cast Dart valve covers and I drilled a hole in the side years ago on my first SR motor and installed a PCV. I was in a motor shop for something and the owner ask me WTF! LOL We welded the hole shut. See where it is welded on the passenger valve cover Also notice how clean the intake plenum runners are on a motor I am taking apart for new heads?
Last edited by gkull; Oct 8, 2013 at 12:27 AM.
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Le Mans Master
Joined: Dec 2003
Posts: 5,727
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From: Fremont CA
I re-engineered the crankshaft ventallation system on my 72 LT-1 years ago after observing the build up of moisture after the Vette sat between outings. Head/intake gaskets can weep while sitting and I live in a humid area. Thinking I didn't want the roller bearings in my rocker arms exposed to water, I reinstalled a PCV system. The system wasn't a closed crankcase vent, both valve covers vented to a catch can, then I put an older factory hi-rise intake on and installed the oil filler tube from a C2 Vette with a PCV valve on that, my moisture problems went away after going to this set-up
Last edited by Solid LT1; Oct 8, 2013 at 01:19 AM.
Racer
Joined: Jul 2013
Posts: 385
Likes: 3
From: Leesburg VA
OK, so I have another question related to this. On my 74, the driver's side has what I assume is the PCV valve with a ribber hose going to the center vacuum port at the base of the carb. The passenger side has a hose that is not hooked to anything because the previous owner installed an aftermarket air cleaner without the port to hook the other end of the hose to. Is this hose the inlet side of the system? If so, would a breather be acceptable here? Or, alternatively, should I figure out how to install the fitting in my air cleaner to hook the hose to?
This issue is way down my priority list of work to do, but the question was out there so I figured I would ask.
John
This issue is way down my priority list of work to do, but the question was out there so I figured I would ask.
John
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
An intake breather/filter on the right-side cover would be preferable to an open tube sticking out of that cover...simply because it would limit the amount of cr@p getting into the engine. But, it could allow some engine vapors to escape that breather under certain conditions.
Still not as good as plumbing that tube up to the air cleaner system you presently have.
Still not as good as plumbing that tube up to the air cleaner system you presently have.
Burning Brakes
Joined: Feb 2012
Posts: 925
Likes: 7
OK, so I have another question related to this. On my 74, the driver's side has what I assume is the PCV valve with a ribber hose going to the center vacuum port at the base of the carb. The passenger side has a hose that is not hooked to anything because the previous owner installed an aftermarket air cleaner without the port to hook the other end of the hose to. Is this hose the inlet side of the system? If so, would a breather be acceptable here? Or, alternatively, should I figure out how to install the fitting in my air cleaner to hook the hose to?
This issue is way down my priority list of work to do, but the question was out there so I figured I would ask.
John
This issue is way down my priority list of work to do, but the question was out there so I figured I would ask.
John
I have a Moroso oil mist/air separator between the PCV valve and the intake connection. It does accumulate some oil in it and it is easy to drain. I don't know if it is 100% effective, because I previously had some intake studs that weren't sealed that were allowing oil to get drawn into the intake.
Drifting
Joined: May 2005
Posts: 1,968
Likes: 44
From: East TN
I recently replace the Edelbrock crankcase breathers that I had on each valve cover because they were seeping oil, making a mess, and dripping onto the headers. I replaced the right one with a chrome breather that is connected to the air filter drop base using a flexible stainless steel tube, so it's supplied filtered air. Here's the fitting I bought for the air cleaner dropbase connection. http://www.jegs.com/i/Edelbrock/350/1205/10002/-1
The left side was replaced with a billet PVC valve which is routed to the large vacuum port on the rear of the carburetor. No more mess.
At some point I may add a catch can setup. But this cleans up the mess for now. Here's the old breather setup that I replaced.
The left side was replaced with a billet PVC valve which is routed to the large vacuum port on the rear of the carburetor. No more mess.
At some point I may add a catch can setup. But this cleans up the mess for now. Here's the old breather setup that I replaced.
Burning Brakes
Joined: Feb 2012
Posts: 925
Likes: 7
Mike80 - Switching from 2 breathers to the PCV/breather (whether on the valve cover or through the filter) puts oil into the intake where it builds up as a hard cruddy mess (technical description) around the intake valves just below the stem, where the obstruction messes up the air flow into the cylinders and if there is enough blow-by, the plugs get a coating too. This is why most racers, etc. run two breathers only, so the performance of their engines doesn't degrade. That's why I have the separator in the line after the PCV valve.
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
The passenger side has a hose that is not hooked to anything because the previous owner installed an aftermarket air cleaner without the port to hook the other end of the hose to. Is this hose the inlet side of the system? If so, would a breather be acceptable here? Or, alternatively, should I figure out how to install the fitting in my air cleaner to hook the hose to?
This issue is way down my priority list of work to do, but the question was out there so I figured I would ask.
John
This issue is way down my priority list of work to do, but the question was out there so I figured I would ask.
John
Drifting
Joined: May 2005
Posts: 1,968
Likes: 44
From: East TN
Mike80 - Switching from 2 breathers to the PCV/breather (whether on the valve cover or through the filter) puts oil into the intake where it builds up as a hard cruddy mess (technical description) around the intake valves just below the stem, where the obstruction messes up the air flow into the cylinders and if there is enough blow-by, the plugs get a coating too. This is why most racers, etc. run two breathers only, so the performance of their engines doesn't degrade. That's why I have the separator in the line after the PCV valve.
Drifting
Joined: Oct 2005
Posts: 1,528
Likes: 148
From: East London/SW Essex UK