PCV use

[bigrob]

If my engine has the setup for a PCV valve & I eliminate it and use a breather on that valve cover, will I have any type of problem? It seems I shouldn't, being it is generally for emmisions purposes, but I wanted some opinions.

Thanks!

[Woodz428]

I'm a strong believer in PCV's, I wouldn't remove it. Some issues that can arise are TOO much crankcase pressures that will create oil leaks in certain areas, as well as blowby from the same build up of pressure. Unless you plan on an evac system plumbed into your exhaust, leave it alone. If you are planning on an evac system, don't, unless it is just for the track.

[bigrob]

Originally Posted by Woodz428

I'm a strong believer in PCV's, I wouldn't remove it. Some issues that can arise are TOO much crankcase pressures that will create oil leaks in certain areas, as well as blowby from the same build up of pressure. Unless you plan on an evac system plumbed into your exhaust, leave it alone. If you are planning on an evac system, don't, unless it is just for the track.

I did think about the pressure side of it, but wondered, if that is one of the functions, why is it not plumbed to both valve covers? I believe my Corvette IS plumbed to both for THAT reason.

[Bob In Ct]

PCVs were never about reducing pressure in the crankcase. Who started this rumor? They were a very early anti-pollution device designed to burn-off the blow-by instead of venting it to the atmosphere.

Leave it on if you want. Remember it leans out the mixture a little. Hook it up below the carburetor.

Bob

[nevermind65]

I had breathers in both valve covers originally. Maybe it was the type of breather I used, but I got sick and tired of smelling the oil fumes when I got on it and finding oil slime all over the valve covers. I hooked up a PVC in one valve cover, and left the same breathers, and voila! Problem totally disappeared.

[Ron61]

I believe that Bob hit it right on the head. I have had both with and without them hooked up and I don't like the oil fumes on the covers plus the smell. On my 1958 Ford, the factory put a tube that plugged into the back of the intake and ran down around the bell housing and just emptied the fumes to the ground. There was always a mess at the bottom of that tube until I extended it about 1" and then the wind going under the car took it away. Since then all of my vehicles have had hoses to both valve covers, usually with a PCV valve in one cover and a twist on cap with the hose going to the air cleaner in the other cover.

Ron

[Woodz428]

In response to the comment about crankcase pressure. I do agree that it was a pollution device to burn the crankcase vapors. However, those crankcase "vapors" add up to a pressure as they accumulate.The breathers allow it to escape, but the draw of the PCV helps remove it. Modern engines wind much higher than the ones that were around when the PCV was first created, it may be that they weren't generating enough pressures to have a problem. I have seen an engine that leaked from various areas until a PCV was plumbed in, so I stand by my position. Sometimes there are side benefits that are not part of the initial application.
One of the reasons that it is applied to only one valve cover is so there can be fresh air drawn in from the other side. I would have to look at the plumbing on the Corvette you mention, but it has to have fresh air tube connected somewhere...possibly on the oil fill tube leading to the intake tract somewhere.

[decapello]

Can you plumb a PVC valve through the intake manifold into the lifter valley, and keep your valve covers vent-less? As Ron61 said the pre PVC equipped engines had a pipe exiting the manifold and dumnping into the atmosphere. So, I'm wondering if I could drill through the manifold in an area that leads to the lifter valley, and plump the PVC from there. Is the lifter valley equalized atomspherically to the crankcase?

I got a nice new set of cast valve covers with no holes, and like the way they look. I really don't want to drill into them.

Thanks, Mike

[Slick61]

I had one on mine, but ended up taking it off as I was having a problem with the PCV sucking oil through the engine... talk about FUMES! I was having to add a quart every 150 miles. My breathers have gauze in them... so they do a pretty good job of keeping the oil off of my polished valve covers. When the gauze gets saturated, I replace them... they're cheap.

[CHANMADD]

There has to be a baffle under the PCV valve to prevent the vacuum from sucking up oil.

[Woodz428]

Originally Posted by decapello

Can you plumb a PVC valve through the intake manifold into the lifter valley, and keep your valve covers vent-less? As Ron61 said the pre PVC equipped engines had a pipe exiting the manifold and dumnping into the atmosphere. So, I'm wondering if I could drill through the manifold in an area that leads to the lifter valley, and plump the PVC from there. Is the lifter valley equalized atomspherically to the crankcase?

I got a nice new set of cast valve covers with no holes, and like the way they look. I really don't want to drill into them.

Thanks, Mike

There are a couple of things that have changed since the advent of PCV's. One is that most early vehicles had a fill tube that wasn't into a valve cover. The early PCV conversions were just an adaptation to existing pieces, in other words they di have the PCV plumbed into the rear of the manifold and used the fill tube to give the proper flow. As it became standard equipment, they simplified the system and installed them into the valve covers, PCV and oil fill. If you look at early engines, most have no holes, because they weren't needed. If you can add a fill tube to your manifold and have an access on the back for PCV, you can run "holeless" valve covers. The 2-4 factory intake on Shelby's have the oli fill tube and a place for the PCV to get plumbed in the back. An intake like that can easily be "correctly" fitted to use a PCV and not have holes in the valve cover. I put correctly in parenthesis because it took, I believe, 3 tries for Shelby to get it right on the '67 GT500s. That is according to SAAC and the pics they sent of the various ways to route them. Originally they had the PCV hooked to the fresh air nipple on the air cleaner and it was worthless...read previous comments regarding leaks. I don't recall, without finding the pics, what the second routing was. So, depending on intake or availabilty of a good fabricator, you should be able to accomplish what you want.

[bigrob]

I am leaving it off! I dont smell any oil fumes and dont rally care if I do. Car is running good with breathers on both covers. Have not had any oil get by the breathers onto the covers either......so far. My Vett's LS-1 motor is NOTORIOUS for sucking oil through the PCV system. So much so, that I had to install 2 catch cans in the line to eliminate all that oil getting into the intake!
Thanks for all the input guy!!

[Ronbo]

There was another impotant reason for PVC, those blowback gasses can thin your oil out as well as making it dirty. Either baffle the port or flip the covers so the PVC is at the front of the engine to stop oil getting sucked in.

Worth having for this reason alone...

[Slick61]

Originally Posted by Ronbo

There was another impotant reason for PVC, those blowback gasses can thin your oil out as well as making it dirty. Either baffle the port or flip the covers so the PVC is at the front of the engine to stop oil getting sucked in.

... couldn't you just swap the PCV & breather from one side to the other, instead of flipping the covers?

[Bob In Ct]

Some of you guys should go to the circle races some weekend. You can look at dozens and dozens of Chevy and Ford small blocks and not see one PCV valve (it's not PVC which is a resin). It's an early anti-pollution device, nothing more. It's not about lowering pressure or preventing thinning oil. If you're getting enough blow-by to thin your oil or produce pressure in your crankcase you will need more than a PCV valve.

Just my $0.02.

Bob

[jwd]

Originally Posted by Bob In Ct

Some of you guys should go to the circle races some weekend. You can look at dozens and dozens of Chevy and Ford small blocks and not see one PCV valve (it's not PVC which is a resin). It's an early anti-pollution device, nothing more. It's not about lowering pressure or preventing thinning oil. If you're getting enough blow-by to thin your oil or produce pressure in your crankcase you will need more than a PCV valve.

Just my $0.02.

Bob

I disagree. Go to the drag races and you'll see that the crankcase is hooked up to the collectors on the headers. They use the venturi effect in the collector to evacuate the crankcase of pressure. That increases HP. http://store.summitracing.com/partde...5&autoview=sku

Jim

[vettestr]

This 1 page will cover all the reasons and history of the PCV or positive crankcase ventilation valve.
http://en.wikipedia.org/wiki/PCV_valve

[Jerry Clayton]

On a 500 in hemi making 1380hp at 9500 we pull a vacume in the mid to high 20 inches from the drysump scavage pumps---there is so much suction from them that we probably could get away with not running a pressure section oil pump--it could suck the oil thru the bearings instead of pumping it with positive pressure.

[Bryan Wilson]

this is how PCV should be setup
PVC installation on a 302

[bigrob]

Well I've been convinced! I am hooking mine back up! more folks for it than not.

Thanks guys!!