To PCV Or Not ?

[Chics LI]

Guys I am trying to get a definitve answer on this ..do I install a PCV or not. I have done a search on this and have seen replies both yes and no.
I have a 351 built not a crate and also not radical. It has the ribbed Cobra aluminum valve covers with a Moroso breather on each side. Engine only has about 500 easy miles so far, (my job doesn't give me too much time to play with it at this time). I have noticed when it is idlleing that there is a little smoke coming from breathers but no misting or visible oil expelled.
Should I leave it as is till engine is broken in or put on a PCV. If I install a PCV should I put it in place of one of the breathers, I have seen breathers with PCV built in to it and connect to vaccum tube on carb base or just leave alone? I can't go to air cleaner, I have oval cleaner with thin element due to lack of hood clearance. Engine has Edelbrock Air Gap intake manifold and this limits hood clearance.
Need a little guidance guys.

Tom S.

[wilf leek]

Tom - have PCV installation on my 408 stroker. Works like a dream - no oil or fumes anywhere.
Plumbed straight into the big port on the carb (thus sees manifold vacuum), on the other valve cover I just have a Ford Motorsport breather.

Pics in my gallery.

HTH

[Ron61]

Tom,

I have had a pvc setup on my stroker since I had it built in 1996 and it is great. As Wilf said, no fumes or anything and it does help get rid of some pressure. Three people here who built cars have since put the pcv on as they were getting oil fumes all over their engine compartments. Some smoke from just a breather is normal. The hot oil builds soime pressure and it has to go somewhere. So far as your oval air cleaner, two of the guys just drilled holes in the bottom and put in a right angle plastic fitting for a hose from the left breather cap to the air cleaner. My pvc valve from the right valve cover goes to the port on the back of the carb mounting spacer.

Ron

[Back in Black]

Most crankcases have a very low positive pressure, and it gets much worse if you romp on it, in my case enough to blow a slight oil mist out the dipstick, (naturally ) right onto the headers!

I installed a billet PCV & breather and a ss hose/AN system, ......breather on the driver's side, (hidden in a billet breather look unit) PCV in the passenger's side, fed into the intake thru a port. You can also feed it into the large unused tube sticking out of most carbs, but since my carb is temporary, it made sense to put it directly into the intake. No leaks now except for a tiny weepage around the rubber grommets, no big deal at all. For the dipstick I bought a nice billet dipstick and ss tube system, perfect now. The stock unit from Ford was not street worthy.

[Excaliber]

Good idea, I wouldn't run without one. I hate all the mist and junk that comes out and gets on my motor.

Ernie

[Bob In Ct]

Hey Tom:
I've got a 351W with no PCV. I have a breather on each valve cover and nothing else. I have no oil on either cover.

Remember, that using a PCV will lean out the mixture. If I had to bet I would think you are better off with a PCV.

Bob

[SCOBRAC]

Ditto, without it is really hard to digest 900-1200 cfm.. but if you aren't (can't) run dual quads it should make a difference until you need to smog it.

[tnlprt]

crankcase pressure comes from compression getting past your rings A PVC valve lets your motor create a vacumn inside the crankcase easing the pressure on gaskets and promoting a better ring seal and yes it does create a slightly leaner mixture but show me one performance engine that is run on the ragged edge of being too lean and you'll see more than a few burnt pistons most are a little on the fat side when it comes to jetting it shouldn't be to hard to rejet after installing pcv valve

[KobraKarl]

I have wondered about this myself as I run 2x4 and have the goose neck breather at the back of the manifold and a pcv to the manifold intake.

is this redundant? and do you think I should ditch the pcv?

[Sizzler]

I have a PCV in each valve cover and a breather front and back on the manifold, though the back breather is currently blocked off.
I inadvertently tested the effects of 1 PCV vs 2 PCV's by leaving one disconnected from the manifold vacuum port. Tremendous better drivability increase from connecting up the second PCV...engine literally ran smoother.

Your experience may vary...

[Whaler]

Hi Guys,

I just started making those connections yesterday after leaving them apart for a year ( engine not running yet)
I ran the PCV in the valve cover to the stub at the back of the carb. On the carb I essentially used another 90 fitting off another PCV valve because I couldn't buy just the 90 elbow. To connect the 2 males I used 3/8" hose.

Now heres the goofy thing. I have the FE Cobra valve covers that came with the single chrome Motorsport valve cover breather.
It has a stub on it that seems a little big on the the O.D.?????
Any suggestions on what to use to connect this to the bottom of my K&N filter bottom??
3/8" Hose fits nicely into the K&N but sure as heck isn't going on or over that breather stub??

Shall I look for a different breather? Look at using a male to male adapter on the line and using 2 different line sizes.

Suggestions on what you guys did on the breather to breather
run would be appreciated.

Maybe not worry about it and skip the connection.
Is this only because they are seeking to introduce air for the crankcase thru a cleaner filterered air source? If so why not stick one of those K&N style filtered breathers in place of the motorsport tincan onto the valve cover and leave it at that?
I kind of hate the look of another 3/8" rubber hose sneaking it's way into my turkeypan anyway. LOL
Tim

[BlueRooster]

Does the PCV allow oil mist into the Carb or intake manifold? If so, does this create a long term problem?

[Whaler]

A functioning PCV will only really open up when the vacuum of the engine allows it. Idle and cruising are when vac is at peak.

The stub I connected to is at the extreme bottom edge of the carb, may as well be on the intake.
My edelbrock RPM doesn't have a stub as far as I can see.

Any oil in the form of fumes/gases is therefore introduced under/after the carb's finer workings and as people say will tend to lean out the a/f mix.

I can't see it being a problem.

Tim

[tommyboy]

Does anyone have an independant runner sytsem such as a Weber 48IDA carb setup, for Ford 351w small block, set up with a pcv? Info and pics would be nice!

[mr0077]

The PCV valve "closes" (goes to minimum flow) at high vacuum (such as idle conditions), and "opens" (max flow) when manifold vacuum drops off, so the amount of flow through the valve decreases at idle to avoid upsetting the idle mixture, and increases at operating RPM, when the relatively small amount of air flow won't have a major effect on the fuel/air ratio. It will pull vapors with oil and other combustion byproducts from the crankcase into the intake manifold...they get burned and exit through the exhaust, with no significant impact on power output I'm told (unless the engine has so much blow-by it is already down on power). The PCV valve is almost always a win-win item for non-race motors IMHO.

[rdorman]

... like I needed to state that

But by creating a vacuum in the crankcase you can actually increase ring sealing and therefore combustion efficiency. I just put a PCV setup on my car. Part because of the fumes and for what I just mentioned. I saw it as a win-win as well.

Rick

[Mr.Fixit]

A PCV valve does not create a vacuum in the crankcase, it merely prevents the pressurization of the crankcase. I like having a 1.25" tube connecting the valve covers, with two breathers standing up off the tube. They end up right next to the aircleaner so the fumes get inhaled and burned anyway.

[427 S/O]

I've debated this for some time, I'm pulling only 6-7 inches at idle, 1000 rpm.
Not sure if I even need one?.

[rdorman]

Told you I didn't need to say it! So no vacuum, but less pressure!

Rick

[mr0077]

Perry, I imagine you already have a "somewhat" lumpy idle, but with vacuum that low, I wonder if a PCV valve might flutter between open and closed air flow, and cause an erratic idle or cmake it worse? I've never heard any info on the point (vacuum or flow-rate) where a PCV valve opens or closes.