Two PCV valves??????
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Senior User
Joined: Oct 2005
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Two PCV valves??????
Does/ has anyone seen an engine with two PCV valves??? I bought a set of valves covers without the holes, drilled one extra in the wrong place and now have one too many. Would having two PCV's be a problem??? Or an advantage???
I currently have two filler caps, but am considering just putting two PCV valves in. Any input???
Craig
I currently have two filler caps, but am considering just putting two PCV valves in. Any input???
Craig
FTE Chapter Leader
Joined: May 2006
Posts: 11,273
Likes: 100
From: North Dakota
u should use some sort of pcv. but i don't see why u can't use one in each cover. or u could get a e-vac kit from moroso. i have a e-vac kit on my pickup and don't have a pcv valve or a breather. i had just breathers on it before and it leaked oil from what seemed like everywere. now it doesn't leak a drop!
Laughing Gas
Joined: Aug 2004
Posts: 964
Likes: 1
From: Roseburg, OR
You can't use one in each valve cover because gasses aren't traveling the same direction through each. The vacuum tube at the base of the carb should have the PCV valve on it. The larger hose which connects to the opposite valve cover and the base of the air cleaner is the fresh air supply to the crank case.
People think PCV is some mysterious system, it's really not. The carb vacuum draws fumes from blow-by out of the crank-case, up through the oil drain-back passages. Fresh air replaces those fumes, and it comes from the air cleaner or a filtered breather if you just have one on the valve cover.
So DO NOT use a PCV filter in both valve covers. It's just a check valve. The one on the fresh air side will suck shut and create a less-than-desireable vacuum situation in your crankcase.
People think PCV is some mysterious system, it's really not. The carb vacuum draws fumes from blow-by out of the crank-case, up through the oil drain-back passages. Fresh air replaces those fumes, and it comes from the air cleaner or a filtered breather if you just have one on the valve cover.
So DO NOT use a PCV filter in both valve covers. It's just a check valve. The one on the fresh air side will suck shut and create a less-than-desireable vacuum situation in your crankcase.
Cargo Master
Joined: May 2007
Posts: 2,071
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From: British Columbia
A friend installed dual PCVs on his 302 as it had excessive blowby. It works fine. He left the existing breather which connected to the air cleaner and cut a new hole for the extra PCV in the valve cover. Now there is a PCV in each valve cover.
FTE Chapter Leader
Joined: May 2006
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From: North Dakota
i thought it would work it dose the same thing as a e-vac kit. just using engine vacume insted of exhaust gas.
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MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
You can't use two PCV valves. The one downstream of manifold vacuum will work as normal but you'll suck the one on the breather-end shut and you won't get any circulation, and you're going to create negative pressure in your crankcase with no natural path for fresh air to come in. go_racing84 is right on the money. You definitely need one though. But NOT two. Draw an engine out on paper with arrows and you'll see it just doesn't work.
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FTE Chapter Leader
Joined: May 2006
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From: North Dakota
have u ever looked at how a crankcase e-vac kit works? mr gasket sells them part# MRG-6002 at summit. they are designed to reduce pressure buildup in the engine crankcase. They provide better piston ring seal, less intake charge contamination, and a reduced chance of oil leaks, while increasing your engine performance.thats what the discription said, i do know they create a negative pressure in the crankcase.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Yes, I have looked at it. It's just an aftermarket PCV system. I see that setup comes with two check valves, but I doubt you'd install them in the same direction, like a dual PCV valve setup. If you install two PCV valves standing straight out of each valve cover, they are fighting each other and defeating the purpose of the PCV system. What would be the point in intalling two check valves backwards? Therefore it appears the e-vac system is different. I haven't used it though, so I can't say for sure. Either way I don't see the point in it. Just because Summit sells it doesn't mean someone should buy it. If 2 PCV valves are such a good idea then why hasn't Ford ever done it in the 40 years PCV valves have been on Ford engines? Just my 2 cents.
You want to build up negative pressure, because that is what cycles fresh air through the engine through the breater filter. But you don't want to build it up indefinitely. Then it looks for another path for something to take the space...an aged oil pan gasket would be a prime victim.
You want to build up negative pressure, because that is what cycles fresh air through the engine through the breater filter. But you don't want to build it up indefinitely. Then it looks for another path for something to take the space...an aged oil pan gasket would be a prime victim.
Last edited by fmc400; Jul 23, 2007 at 06:24 PM.
Cargo Master
Joined: May 2007
Posts: 2,071
Likes: 36
From: British Columbia
Hi fmc400:
I think that the scenario you imagine is replacing the fresh air breather with a second PCV.
My friend did not alter the fresh air breather, he drilled another hole in the valve cover and installed an additional PCV valve.
I think that the scenario you imagine is replacing the fresh air breather with a second PCV.
My friend did not alter the fresh air breather, he drilled another hole in the valve cover and installed an additional PCV valve.
Postmaster
Joined: Aug 2001
Posts: 4,270
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From: Delaware
Originally Posted by Beanscoot
Hi fmc400:
I think that the scenario you imagine is replacing the fresh air breather with a second PCV.
My friend did not alter the fresh air breather, he drilled another hole in the valve cover and installed an additional PCV valve.
I think that the scenario you imagine is replacing the fresh air breather with a second PCV.
My friend did not alter the fresh air breather, he drilled another hole in the valve cover and installed an additional PCV valve.
You could put two PCV valves in one cover and tee the hoses into the manifold, with one breather in the other cover.
You shouldn't put a breather and a PCV valve in the same cover.
FTE Chapter Leader
Joined: May 2006
Posts: 11,273
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From: North Dakota
well this is going to go on and on and on.. but with the e-vac kit you do install the kit on both valve covers so it does pull air out of both of them. it doesn't have any way of letting "fresh" air in. with out any pcv or e-vac kit on my pickup it leaked oil all over the place. it would even push the oil dipstick out! that was with just 2 breathers on the valve covers. i didn't want to run a normal pcv valve because it sucks the "dirty" air out of the crankcase back into the intake. so i used te e-vac kit. it uses echaust gases passing the opening in the pipe to pull the air out og the crancase. and it stopped my oil leaks and my oil dipstick from coming out. it keeps a constant vacume on the crankcase. so the way i look at it the 2 pcv valves would work the same way. except in the original ? bareaneye would have a brather and a pcv on one valve cover, letting in "fresh" air like some of u say needs to be done. so it should work fine the way i figure it.
Elder User
Joined: Jun 2003
Posts: 886
Likes: 1
From: Houston/Hope BC
E-vac are acceptable for the race track. I kinda care a little about the air I breathe so I'm NOT a big fan of discharging blow-by gasses direct to the atmosphere.
Breather caps literally suck dirt in.
A proper PVC system will have a valve calibrated for the engine/carb and a fresh air intake inside the air cleaner element to let CLEAN air into the crankcase.
At WOT, zero manifold vacuum, flow REVERSES on the fresh air line. Both connections will be moving blow by gases back to the engine for combustion. This is the most often overlooked operating state.
GL
Breather caps literally suck dirt in.
A proper PVC system will have a valve calibrated for the engine/carb and a fresh air intake inside the air cleaner element to let CLEAN air into the crankcase.
At WOT, zero manifold vacuum, flow REVERSES on the fresh air line. Both connections will be moving blow by gases back to the engine for combustion. This is the most often overlooked operating state.
GL
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