JBR

350 engine, mild cam, comp heads, roller rockers, raised intake, demon carb. I have no pvc valve set up at all. just breather caps on both valve covers. I was told this was a bad idea. Should I run a pvs valve and line to the bottom of the air filter? Any ideas? :cheers:

Brettmc

You'd be better off if you had some kind of PCV setup.

Brett :thumbs:

joeveto

You need to have a PCV system. Without it, your oil will fail a lot faster. You need a way to get all the moisture, corrosives, etc out of the lubrication system. When the oil heats up, this garbage needs a place to go.

Pop a PCV valve into the valve cover, and run the hose to the vacuum port at the base of your carb.

Takes ten minutes, and your engine will thank you. :yesnod:

Vetterodder

I agree with Brettmc and joeveto, a functioning PVC is a good thing. One of the benefits is better ring seal. The engine won't know the difference if the fresh air source is through the air cleaner or through a breather but there is an advantage to using the air filter. Under some circumstances, crankcase fumes will exit through the fresh air source. If vented to the air cleaner, those oily fumes will be reburnt. If vented to a breather, those fumes can leave an oily film in the engine compartment.

cardo0

Early cars ran with only breathers. Sometime in the 60's Detroit started installing PVCs on cars but the carburetors are adjusted for the controlled leak of the PVC. You should be fine either way as a crankcase evacuation system gets complicated real fast. If you choose PVC insure you use a baffled VC hole to minimize valve oil splash into PVC/intake. :yesnod:

standup

Cardo0......you've always given excellent advice.....is the sea air getting to you :lol: ........PCV is an easy and cheap setup.......line in, line out and burn off all the baddies........

.........save the breathers for the hotrodders in their Furd deuces....... :cheers:

JBR

Thanks Guys: I'm looking at Summit -Billet breathers- 1 standard and 1 w/pvc in it. I need to find out the size of the hole in the VC theses call for 1.220" :cheers:

Eddie 70

I swapped valve covers when I rebuilt. I now have a breather in one valve cover and one PCV in the other going to the carb base. I am thinking this is the correct setup, am I right?

JBR

Eddie 70 That sounds good from what everyone is telling me. I don't think I have a pvc connection on the demon carb. so I might have to use the line connection on the bottom side of my air cleaner housing, which I have pulged off.. Also I noticed no fuel filter, all stainless braided lines, but no filter between the pump and carb. :confused:

L79vette

The connection on the air cleaner won't work. You need to connect to vacuum, like the carb port. This will suck the blow-by into the intake, which sounds bad but really isn't.

I had to add a carb spacer with a vacuum line, because my Holley 4150HP carb also had no vacuum connection.

Another possbility is to use the power brake vacuum port on the intake, but that sucks all the blow-by down the #8 intake runner, which fouls that plug pretty quick on mine.


[Modified by L79vette, 5:26 PM 5/4/2004]

Summerfun

JBR,
You do want a PCV valve!
Positive Crankcase Ventilation is exactly what it says.....
When you start your engine and start driving, the engine heats up.
Hot air expands and it has to go somewhere hence the PCV valve, otherwise you might end up with bearing problems due the high pressures in the crankcase.

I had one in my intake, because I wanted to try and hide as many hoses as
possible.....burnt 8 quarts of oil in 200 miles
:mad
Blocked it off and put it in my nice Dart Aluminium Valve cover....no more oil burning, cleaner plugs, more horsepower.......smacked the nose of my baby into a pole :cry :cry
Still waiting for my new bumper cover to come from Michigan....

cardo0

:rolleyes: Okay I'll to explain this PVC sys. The PVC is a controlled leak. It runs from the valve cover to a vacuum source - usually the intake to a fitting on the intake or at the base of carb. When at idle and vacuum is high but piston blow by is small the leak is throttled small due to the PVC seat design. When vacuum is low while engine speed/load is high a spring forces PVC to open more to remove more of the blow-by gasses. Once the engine is stopped/no vacuum the spring forces the PVC fully shut. You still need a breather on the other VC - and it should be filtered - to draw air through the opposite cyl head into the crankcase/engine and out the PVC into the intake. The filtered air source can be from the aircleaner as is my '74. The carb needs to be calibrated for this also but I rarely hear of problems.
And thank-you for the compliment standup but what I ment by exh evacuation system is a system that uses either a dedicated vacuum pump (with oil separator) or a exhaust flow scavengening sys using check valves connected to header evacuator fittings. And these too would need a filtered air source. The hi po racers use fewer piston rings for less parasitic internal engine drag and have more blow-by. ;)

KenSny

LORD HAVE MERCY! What a load of mis-information.

Of course you do not want to BLOCK off the breather holes.... that's just plain stupid. But open element-filter type breathers in each valve cover will work PERFECTLY fine......

Summerfun

Excuse me??
I had the PCV directly on the intake and it was burning oil through the carb like crazy.
So I took it out of the intake, blocked the hole and re-installed it on the valve cover. Did not want it there at first for the sake of looks.

What is misinformation? I would love to learn more about the inner workings of an engine so I would be much obliged if you could explain my ignorance and make me undestand!

427V8

I don't know if you can MAKE you understand but we can try... :-D
Look below for inline comments

>JBR,
>You do want a PCV valve!

Yep, unless you are big into racing I agree

>Positive Crankcase Ventilation is exactly what it says.....

So far so good

>When you start your engine and start driving, the engine heats up.

Um well yes the engine does heat up but...

>Hot air expands and it has to go somewhere hence the PCV valve,

The air that you are sucking out of the crankcase is stuff that leaks past the rings during the compression / power stroke. this stuff is unburned and burned fuel and air.
If you don't pull that stuff out then your crankcase will be stuffed with the above mentioned gasses, contaminating the oil and pressureising it possibly causing oil leaks.

>otherwise you might end up with bearing problems due the high pressures >in the crankcase.

The bearings don't care about the crankcase pressure, but the rings will seat better if there is a lower pressure in the crankcase ( but at WOT I doubt there's any vacuum to speak of )

Speaking of WOT, that is the reason the other valve cover is connected to the air cleaner. At WOT the PCV is basically closed ( since there is very little manifold vacuum ) so the blowby will get sucked through the other valve cover and into the carb that way. Not as effective, but cleaner

>I had one in my intake, because I wanted to try and hide as many hoses as
>possible.....burnt 8 quarts of oil in 200 miles

The PCV valve needs a baffeled hole, there's a lot of oil mist in a running engine and without a baffle that mist will get sucked into the PCV...


> :mad
>Blocked it off and put it in my nice Dart Aluminium Valve cover....no more >oil burning, cleaner plugs, more horsepower.......

With your setup I suppose so, with a good setup there should be no diff

Summerfun

Oops.... I meant rings, not bearings. Sorry!
It's obvious that pressure from within the crank case or blow by from the combustion chamber could have an effect on the piston rings and not the crank bearings. I meant rings and wrote bearings.

But.....now you have me worried!!!
"Blocked it off and put it in my nice Dart Aluminium Valve cover....no more >oil burning, cleaner plugs, more horsepower.......

With your setup I suppose so, with a good setup there should be no diff"

What do you mean "with a good setup there should be no diff"?
I hope you are just talking about a baffle!!

That is a brand new short block that was balanced at the shop that I bought it from. I added my top end. I figured that it is just oil mist from the crank thrashing around in there that is throwing high amounts of oil onto the exposed PCV valve on the intake that was causing the problem. You make me think that there is something else going on in there.
I did not want to go through the trouble of taking the intake oof to make a baffle, so I blocked it off and put the PCV on the opposite valve cover. The breather cap is on the other side.

That engine has less than 500 miles on it....the first 200 ate a lot of oil, but it is fine now. What are you saying that I am missing?

BTW, I do appreciate the posts......that is what it is all about

tshort

I think you're mixing descriptions up and confusing us all. You took the PCV off the intake??? Don't you mean you took it off of the valve cover? That's a big difference and completely wrong.

Summerfun

No, it was on the intake and kept sucking oil into the carb and burning it in the combustion chambers. Then black smoke out through the side pipes on getting on the throttle as well as getting off of the throttle.

I then took it off of the intake, blocked the hole in the intake and made a new hole in the valve cover where I then installed the PCV valve.

After that she stopped burning oil and stopped smoking.

Older Than Dirt

This is the correct way. I've never heard of installing a PCV valve in the intake!. How did you do that in a threaded hole, how did you seal the PCV valve mounted in the intake?

Summerfun

"I've never heard of installing a PCV valve in the intake!."
You haven't seen an older Buick??

I don't understand why this is so difficult to understand!!!

The PCV valve was on the intake manifold in the area between the carb and the firewall of my car. A hole was drilled big enough to install a rubber grommet and the PCV valve was then pushed into the rubber grommet.

So, it was on the back part of the intake manifold overlying the camshaft.
Presumably the camshaft was throwing oil up into it which was then sucked through the carb via the vacuum port.