BigBadRed

As my 76 approaches completion, I am looking at cleaning up the engine compartment. Presently I need vacum lines for headlights, powerbrake, transmission, pcv, map sensor, and hvac. I would like to replace the pcv with the breathers you just stick on top of the valve covers. Does this affect anything?

427V8

No but it's stinky and you tend to get an oil mist all over everything...

Use the PCV and breather tube together. Don't use just the PCV with a breather either, the PV will suck dirt into the engine :U

djcwardog

IMHO you definitely need the PCV valve. Make sure it is properly plumbed to the correct vacuum source - no leaks. If you do, you will get a freer-revving engine that does not force oil out past your seals due to pressure build-up in the block from the rotating parts. On my '73 I have a PCV that has a "T" fitting on it. Once I replaced the hose that ran from the PCV down to the charcoal canister, my engine used less oil and ran better. The PCV is one of the few old-era emission parts that is worth keeping.

flynhi

djcwardog,
Help me understand why the T fitting to the canister helps you. As I understand your plumbing, in normal, low rpm, high vacuum conditions, you are sucking only from the canister. In high rpm, low vacuum, you are blowing into the T and into the plenum and canister. Do I have this right?

carl a

i thought the canister hose ran to the gas vent (little black box on the tank of my 73)-what does this have to do with the pcv valve and using oil??

MARKUS_P

That is absolutely right, Carl.
The PVC has nothing to do with the carcoal canister, at least not on my 76.
The pvc valve is connected to one of the two valve covers. Trom the PVC valve a vacuum line runs to the carb (in my case Edelbrock Performer)
The carb sucks out the oil mist through the PVC valve and adds the mist to the air/fuel mixture which goes down into the combustion chambers where it is burnt.
To prevent creating vacuum in the engine due to sucking air through the PVC all the time a valve cover breather should be mounted on the opposite side valve cover where fresh air is able to enter the engine.
That´s all the magic about it. Bad oil mist is burnt, fresh air is sucked into the engine through the breather and our environment is kept cleaner.

I should use spell check more often :rolleyes:


[Modified by MARKUS_P, 6:10 AM 10/31/2003]

427V8

Which brings up a question...

Why not seal the other valve cover and use the PCV to pull a small vacuum in the crankcase?

Unless it because at WOT there isn't much vacuum??

Fevre

There is no vac through the pcv at WOT, since there is no vac in the system the check ball drops and close the valve off. Once the vac level reaches the rating of the pcv the the check ball is sucked up and the carb starts to draw air though the system.

honaker

Here is the deal. It is desirable to pull vacuum on the crank case at any rpm level. It helps seal the rings and also prevents oil leaks. I drag racing they plumb a line from both headers to the each valve cover. At high rpm, the scavange effect from the headers draws a vacuum on the crank. On a street car, most ov your driving is done at lower RPMs. A great source of vacuum at that RPM is the intake system. Most street cars already have this system in place but with a littlke clean up, it will work better and look cooler.

Several aftermarket companies make breathers with a nipple on the side for a hose. Simply run a hose to the bottom side of your air clear. You can also do the same thing with the PVC or just a simple plastic 90 degree elbow.

If you use the PVC, i would drill out the check valve at the bottom so that you have a steady vacuum draw.

There ar a lot of different ways that you could dress it up to make it look nice. If you have a 14" air cleaner, most of the stuff will be hidden under the air cleaner.

Anyway, that's my 2 cents. :smash:

MARKUS_P

Well, I think you would decrease the effectiveness of the whole system.
The only reason why the oil mist gets into the carb is because the pressure in the crank case and in the heads is bigger than the pressure at the carb.
That´s why all the fumes tend to go through the PVC.
If you have equal pressure conditions at the engine and at the carb, you won´t suck anything up.
The carb would suck as strong as it could until the pressure in the crankcase is equal to the one of the carb. At this point no more fumes will be sucked into the carb. You should definitely have a fresh air intake :yesnod:

honaker

The whole point is to put the crank case under vacuum. A simple PVC by itself does not supply vacuum, it is only a check valve of sorts. if you run a line from the valve cover to the crank caes you have effectively accomplished nothing. The atmosphereic presure is the same/nearly the same under the valve cover as in the crank case.

Just as long as you get a vacuum source from anywhere is desireable. Whether you spend a couple hundred dollars on a vacuum pump, use the headers as a scavange source(not recommend for the street, at low rpm there is a possiblity it could pressurize the crank case if not plumbed correctly) or the intake system.

carl a

i have a pcv with a hose going to the intake man. so what your saying is to get a pcv that has another port or add a nipple in line with a port and run that hose to the bottom of the air cleaner-is this correct? will this lessen oil comsumption?- i use 1 quart per 1,000 miles-depending how i drive the car(sometimes more when i really stomp on it ..like on vette runs) would this new hose routing help oil consumption?

honaker

Depneding on the sorce of your oil consumption. It will place the crank case under vacuum, which means that as the pistion is being forced into the bore it is less likely for oil to be forced passed the rings into the cylinder. It is also less likely that oil will leak from the gaskets around the oil pan and other places. With the crank caes under vacuum the out side air will be trying to get in the crank instead of the oil getting out. Consider this, if you have a lot of leaks then you won't get the advantage of a good ring seal on the pistons also, if your rings are worn out a vacuum will not help that much.


You can connect it to the underside of your aircleaner or to the intake manifold. Connecting to both is not nessary. It's the same vacuum source.

Understand this, at high RPMs this set up is less effective because of vacuum loss, also, if you are running a monster cam this is less effective.


[Modified by honaker, 10:17 AM 10/31/2003]