Are PCV's necessary? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

lyrikz · 09-26-2008, 04:07 PM

I have a 71 chevy. 454. Valve covers both have breathers on them. There is a spot coming off my carb. that i can add a PCV to, but is it even necessary?>? I dont have emissions or anything like that and isnt the breathers allowing any crank pressure out???

thanks.

dwcsr · 09-26-2008, 04:16 PM

Yes they are very neccessary.
Their main function is to draw off any unburned gasoline that make make it by the rings or bad pump and vent it back into the engine. If you have ever seen a oil pan grenade and blow off an engine you know how useful that $4 part is. Having breathers on a valve cover and no PVC helps with the pan detenation process.

Vacuum in the crank case also helps seal the rings.

cdowns · 09-26-2008, 04:58 PM

you can run the 2breather setup,many do. but the engine is alot happier with the PCV system hooked up and working correctly

cparman · 09-26-2008, 05:10 PM

The PCV valve was the very first emissions control device installed on cars back in the 50's. Yes they are necessary!! I have a breather in one valve cover that has a tube attached to the bottom of my air cleaner, so the engine is getting clean filtered air. The PCV is in the other valve cover. SO, the PCV draws air into the engine on one side, and thru the engine to the PCV valve which gets it vacuum from the carb clean filtered air to keep the engine crankcase unburned gas free, and ALSO makes sure that there is no pressure building in the engine, this will keep it from leaking oil from perfectly good gaskets. I see many cars at my shop with oil leaks, and one of the first things we do is to make sure that the PCV system is working. It is the culprit of a many a oil leak. YA NEED ONE

lyrikz · 09-26-2008, 05:22 PM

Quote:

Originally Posted by cparman

The PCV valve was the very first emissions control device installed on cars back in the 50's. Yes they are necessary!! I have a breather in one valve cover that has a tube attached to the bottom of my air cleaner, so the engine is getting clean filtered air. The PCV is in the other valve cover. SO, the PCV draws air into the engine on one side, and thru the engine to the PCV valve which gets it vacuum from the carb clean filtered air to keep the engine crankcase unburned gas free, and ALSO makes sure that there is no pressure building in the engine, this will keep it from leaking oil from perfectly good gaskets. I see many cars at my shop with oil leaks, and one of the first things we do is to make sure that the PCV system is working. It is the culprit of a many a oil leak. YA NEED ONE

Sounds good.. PCV it is...

PanelDeland · 09-26-2008, 05:36 PM

The name says it all
P=Positive-that's good
C=Crankcase-a modified box full of expensive parts
V=Ventilation ya gotta have air.

70rs/ss · 09-26-2008, 06:04 PM

As said several times already, yeah you should run one. High end hp machines, actually pull major vacuum to build a more positive seal around the rings (and can add 5-10% more hp), but this is in extreme motors. On a stock or even a 500hp BBC the positive ventilation can still help evacuate blow by (all motors do it, some more than others), and it'll help promote a positive seal for your rings (not a ton more power, but every bit helps) and will prevent explosive gases from filling up the underhood area, as well as helping the motor to run cleaner and more efficient. Sorry, for the long answer after it had been answered several times, but this is free and easy power just waiting (and a lot safer too!!)

Longhorn Man · 09-26-2008, 06:08 PM

to simplify an explination...

You have the kitchen that is filled with smoke. you have 2 windows in the kitchen.
1 open both windows
2 open both windiws, and put a window fan in one of them blowing the smoke out.

The PCV does the job of the fan.

When you only have vents, or the old style road draft tube, the oil gets contaminated with acids that form as a natural byproduct of the combustion. The PCV sucks it out, along with trapped humidity, and the aformentioned blow by.
On the other valve cover, you need a breather to let clean air in. The easy way, is just a chrome Mr Gasket breather. The better way would be a 3/8 hose going to the air filter to pick up air that has already been filtered, and is clean.

Dusty_case · 09-26-2008, 08:08 PM

OK but what is the best way to check your Pcv to see if it is working right?

**leddzepp** · 09-26-2008, 08:16 PM

in a word...YES

cparman · 09-26-2008, 08:41 PM

Hey Dusty case!! Start the engine, and If you leave the PCV in the valve cover, and pull the breather out of the other valve cover, and place a small piece of paper towel over the hole where the breather was, and you see the paper towel depress ( suck into the hole ) you know it works!

Dusty_case · 09-26-2008, 08:45 PM

thank you cparman I will try that later on

Longhorn Man · 09-27-2008, 12:41 AM

pull the valve out and shake it. If it rattles, then it's fine.
If you have any question, it's only like 5 bucks.

70GMCer · 09-27-2008, 07:18 AM

Here is some interesting reading. Pretty much what everyone has said, but with a little more info. http://en.wikipedia.org/wiki/PCV_valve

Also, make sure that you install that PVC in the valve cover that has the baffle under it. If not, oil can come up thru the PVC valve.

ChevLoRay · 09-27-2008, 03:22 PM

An internal combustion engine is merely an air pump. In order to compress the air, it has to breathe. All of the breathing that needs to happen, needs somewhere for the excess crankcase pressure to vent. Prior to PCV valves, engines had a "road draft tube". If you've ever seen an engine that had one, especially when it was nighttime, you would frequently see the smoke from the crankcase as it came out under the car body.....if it had some blow-by. Engines back in the day, didn't last like these engines do today. So, seeing the blow-by coming out of the tube wasn't a biggee. Virtually all of the engines did it. Sometimes, the oily vapor was wet...and would drip on the road and in the garage and on the street and driveways where you parked. It was just another way to track your movements.

I think the Privacy Laws were drafted to prevent oil leakage from engines and that required the PCV system to be installed on all new vehicles.....makes as much sense as some of the other enviromnental laws we have to endure....

kevncar · 09-27-2008, 08:46 PM

When I first bought my truck the PO had a rag stuck in one hole and an oil fill cap that fit real tight in the other. When I got home and noticed this (and the fact that the end of the rag almost caught on fire from the hedders) I looked around for a breather I used to have and couldn't find it. I put another oil filler cap i had in the hole and ran to the parts store to grab a breather. I heard a loud bang like a rock hit the underside of the hood on the way. when I got the breather and opened the hood to replace one of the fill caps...one was missing. This wasn't a high rpm, or long trip either...just a putt through town. They can really build some pressure quick.

09-26-2008, 04:07 PM	#1
lyrikz PITbut Join Date: Sep 2007 Location: monroe washington Posts: 3,055	Are PCV's necessary? I have a 71 chevy. 454. Valve covers both have breathers on them. There is a spot coming off my carb. that i can add a PCV to, but is it even necessary?>? I dont have emissions or anything like that and isnt the breathers allowing any crank pressure out??? thanks.

09-26-2008, 04:16 PM	#2
dwcsr Hollister Road Co. Join Date: Apr 2005 Location: Houston Posts: 6,131	Re: Are PCV's necessary? Yes they are very neccessary. Their main function is to draw off any unburned gasoline that make make it by the rings or bad pump and vent it back into the engine. If you have ever seen a oil pan grenade and blow off an engine you know how useful that $4 part is. Having breathers on a valve cover and no PVC helps with the pan detenation process. Vacuum in the crank case also helps seal the rings.

09-26-2008, 04:58 PM	#3
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: Are PCV's necessary? you can run the 2breather setup,many do. but the engine is alot happier with the PCV system hooked up and working correctly __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

09-26-2008, 05:10 PM	#4
cparman sharp as a marble Join Date: Jan 2007 Location: atlantic beach,florida Posts: 1,082	Re: Are PCV's necessary? The PCV valve was the very first emissions control device installed on cars back in the 50's. Yes they are necessary!! I have a breather in one valve cover that has a tube attached to the bottom of my air cleaner, so the engine is getting clean filtered air. The PCV is in the other valve cover. SO, the PCV draws air into the engine on one side, and thru the engine to the PCV valve which gets it vacuum from the carb clean filtered air to keep the engine crankcase unburned gas free, and ALSO makes sure that there is no pressure building in the engine, this will keep it from leaking oil from perfectly good gaskets. I see many cars at my shop with oil leaks, and one of the first things we do is to make sure that the PCV system is working. It is the culprit of a many a oil leak. YA NEED ONE Last edited by cparman; 09-26-2008 at 05:11 PM.

09-26-2008, 05:36 PM	#6
PanelDeland I am a Referee of life. Join Date: Jun 2000 Location: Greensboro N.C. Posts: 13,992	Re: Are PCV's necessary? The name says it all P=Positive-that's good C=Crankcase-a modified box full of expensive parts V=Ventilation ya gotta have air. __________________ The 47-present Chevrolet and GMC Truck Message Board Network,it's owners,moderators,members,and associates of any type should not be held responsible for my opinion. You can't fix stupid,not even with duct tape. "My appearance is due to the fact that "GOD" does punish you for having too much fun!" Barrett-Jackson has perfected alchemy,they make rust into gold! "You can lead a horse to water but you can't saddle a duck" "Cleverly disguised as a 'Responsible Adult' "Sometimes your Knight in shining armor is just a retard in tinfoil"

09-26-2008, 06:04 PM	#7
70rs/ss Registered User Join Date: Dec 2004 Location: Northern AZ Posts: 7,270	Re: Are PCV's necessary? As said several times already, yeah you should run one. High end hp machines, actually pull major vacuum to build a more positive seal around the rings (and can add 5-10% more hp), but this is in extreme motors. On a stock or even a 500hp BBC the positive ventilation can still help evacuate blow by (all motors do it, some more than others), and it'll help promote a positive seal for your rings (not a ton more power, but every bit helps) and will prevent explosive gases from filling up the underhood area, as well as helping the motor to run cleaner and more efficient. Sorry, for the long answer after it had been answered several times, but this is free and easy power just waiting (and a lot safer too!!)

09-26-2008, 06:08 PM	#8
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: Are PCV's necessary? to simplify an explination... You have the kitchen that is filled with smoke. you have 2 windows in the kitchen. 1 open both windows 2 open both windiws, and put a window fan in one of them blowing the smoke out. The PCV does the job of the fan. When you only have vents, or the old style road draft tube, the oil gets contaminated with acids that form as a natural byproduct of the combustion. The PCV sucks it out, along with trapped humidity, and the aformentioned blow by. On the other valve cover, you need a breather to let clean air in. The easy way, is just a chrome Mr Gasket breather. The better way would be a 3/8 hose going to the air filter to pick up air that has already been filtered, and is clean. Last edited by Longhorn Man; 09-26-2008 at 06:11 PM.

09-26-2008, 08:08 PM	#9
Dusty_case Registered User Join Date: Apr 2008 Location: spokane valley wa Posts: 112	Re: Are PCV's necessary? OK but what is the best way to check your Pcv to see if it is working right? __________________ 1968 c10 250/3spd

09-26-2008, 08:16 PM	#10
leddzepp Moderator Join Date: May 2007 Location: Southern Cal Posts: 20,117	Re: Are PCV's necessary? in a word...YES

09-26-2008, 08:41 PM	#11
cparman sharp as a marble Join Date: Jan 2007 Location: atlantic beach,florida Posts: 1,082	Re: Are PCV's necessary? Hey Dusty case!! Start the engine, and If you leave the PCV in the valve cover, and pull the breather out of the other valve cover, and place a small piece of paper towel over the hole where the breather was, and you see the paper towel depress ( suck into the hole ) you know it works! Last edited by cparman; 09-26-2008 at 08:42 PM.

09-26-2008, 08:45 PM	#12
Dusty_case Registered User Join Date: Apr 2008 Location: spokane valley wa Posts: 112	Re: Are PCV's necessary? thank you cparman I will try that later on __________________ 1968 c10 250/3spd

09-27-2008, 12:41 AM	#13
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: Are PCV's necessary? pull the valve out and shake it. If it rattles, then it's fine. If you have any question, it's only like 5 bucks.

09-27-2008, 07:18 AM	#14
70GMCer Senior Member Join Date: Apr 2005 Location: Joppa, Maryland Posts: 4,408	Re: Are PCV's necessary? Here is some interesting reading. Pretty much what everyone has said, but with a little more info. http://en.wikipedia.org/wiki/PCV_valve Also, make sure that you install that PVC in the valve cover that has the baffle under it. If not, oil can come up thru the PVC valve. __________________ 1997 GMC Sierra Ext 1965 Mustang Last edited by 70GMCer; 09-27-2008 at 07:19 AM.

09-27-2008, 03:22 PM	#15
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: Are PCV's necessary? An internal combustion engine is merely an air pump. In order to compress the air, it has to breathe. All of the breathing that needs to happen, needs somewhere for the excess crankcase pressure to vent. Prior to PCV valves, engines had a "road draft tube". If you've ever seen an engine that had one, especially when it was nighttime, you would frequently see the smoke from the crankcase as it came out under the car body.....if it had some blow-by. Engines back in the day, didn't last like these engines do today. So, seeing the blow-by coming out of the tube wasn't a biggee. Virtually all of the engines did it. Sometimes, the oily vapor was wet...and would drip on the road and in the garage and on the street and driveways where you parked. It was just another way to track your movements. I think the Privacy Laws were drafted to prevent oil leakage from engines and that required the PCV system to be installed on all new vehicles.....makes as much sense as some of the other enviromnental laws we have to endure.... __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

09-27-2008, 08:46 PM	#16
kevncar Active Member Join Date: Dec 2002 Location: Atwater, CA Posts: 259	Re: Are PCV's necessary? When I first bought my truck the PO had a rag stuck in one hole and an oil fill cap that fit real tight in the other. When I got home and noticed this (and the fact that the end of the rag almost caught on fire from the hedders) I looked around for a breather I used to have and couldn't find it. I put another oil filler cap i had in the hole and ran to the parts store to grab a breather. I heard a loud bang like a rock hit the underside of the hood on the way. when I got the breather and opened the hood to replace one of the fill caps...one was missing. This wasn't a high rpm, or long trip either...just a putt through town. They can really build some pressure quick. __________________ Kevin 72 Chevelle 67 C10...454/TH400 Build Thread:http://67-72chevytrucks.com/vboard/s...d.php?t=193961



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