PCV valve setup

[DANNY8]

I wanna plumb the PCV back into the intake but not 100% sure how to go about it. So far I've set it up so both rocker covers go into one line, which then goes to the catch can, then the catch can is just venting to the atmosphere. Can I just run a line straight from the catch can to the spacer under me carby?

Or do I have to actually use a PCV valve in the line somewhere?

Also, the line from the charcoal canister, does that just get hooked up to a vacuum port on the carby?

[VK SL 3800]

What ive heard people do is run the vent to a vacuum port and have a line running from the bottom of the catch can and modify the fuel pump blanking plate to have a return line for any oil to go back to the sump. (unless youve got a mechanical pump).

The charcoal canister line runs to a vacuum port on the carby and is purged under certain conditions. < Straight from my workshop manual
So im guessing its not under vacuum at all times.

[Guzzoline addict]

Leave it the way it is or ,Run one line from a rocker cover to the catch can and have the can venting with small filter ,then run a line from a pcv on the opposite rocker cover to manifold vacuum. You can not run both rocker covers inline.

[DANNY8]

Here's a pic so ya can see wat I mean with how I have the PCV setup at the moment.



I have both rocker covers going into a t-piece then into the catch can which vents. But I wanna run a hose where the air filter on the can is to the base of the carby to make it legal. I'm not to worried about having a drain back system for the oil just yet, just wanna get the pcv sorted. If I run a hose straight from the can (where the filter is) to the base of the carby, wat will that do to my vacuum as it will be getting the pressure from the crank case, obviously not enuf to make the intake pressurised, but will it work against anything?

[ari666]

ok its early, so if this answer is wrong, ima blame coffe-withdrawls:

PCV should be attached onto the large vacuum port on the rear of the base of your holley, and it has full vacuum drawn from the base of the secondarys. you MUST have a PCV (but in your case 2, one in either rocker cover) or you will be losing manifold vacuum by constantly sucking in crank case fumes. now the reason i am not sure the answer is right is cos' for the life of me i cant remember which way the pcv closes... from memory if you suck on the pcv it locks? and if you blow on it its free? or is it the other way round.

cant remember, sorry useless answer.

[dirt drifter]

i think the pcv is open under vacuum/light load running then closes up under no vacuum/high load running so that no oil gets mixed with the incoming air/fuel when the motors copping a hiding. oil mist can induce pinging apparently.

danny8, i see no problem with running a decent diameter bit of hose with a pcv valve from your catch can breather to the carby vacuum port

[Guzzoline addict]

Just noticed i got i wrong in my first post so ignore that. I think to make it legal ,You run one hose from the pcv valve on a rocker cover to the the catch can then a hose from the catch can to manifold vacuum,then have a hose from the opposite rocker cover to the air fliter(You might get away with just having a fliter on the rocker cover). Just make sure you dont have any vacuum leaks on the catch can.This way air should get draw in one rocker cover and vacuume the crank gasses out the other ,while catching the oil before the vacuum goes into the manifold

[DANNY8]

Thx for the replies.

Just noticed i got i wrong in my first post so ignore that. I think to make it legal ,You run one hose from the pcv valve on a rocker cover to the the catch can then a hose from the catch can to manifold vacuum,then have a hose from the opposite rocker cover to the air fliter(You might get away with just having a fliter on the rocker cover). Just make sure you dont have any vacuum leaks on the catch can.This way air should get draw in one rocker cover and vacuume the crank gasses out the other ,while catching the oil before the vacuum goes into the manifold

Just sussed out a vid on youtube which pretty much said everything that u said. It said that the PCV valve must be setup so the vacuum opens it, not the crankcase pressure.

Will I lose power from having it hooked up? As if it's sucking in air, the pressure from the crankcase would normally be getting sucked through the carby?....as in if the PCV is vented how I have it at the moment, there would be more air going through the carby? So having the PCV hooked up properly is pretty much a big vacuum leak hey?

And I'm still not sure about the charcoal canister. I don't understand this 'purge' thing lol. Again it seems like it works as a vacuum leak. As the charcoal canister is hooked up to the fuel tank, so vapours flow through, but then the tank's breather is gonna be sucking in air to compensate.....so yeah, it would be like a vacuum leak??

[ari666]

there is meant to be a little metal filter on the front of the quadrajet. it has two lines, one is the fuel in and the other is the carbon-can return. without that filter the carbon-can will be incomplete, so you may struggle with that one.

[Guzzoline addict]

Not a 100% sure on how it effects performance,but i think its just a vacuum leak. On standard engine the loss of vacuum doesnt effect it that much .A stardard engine has lots of vacuum at low revs and as long as the vacuum leak effects all cylinders equally( e.g the pcv valve is attached under the carby and not on a intake runner ,so the lean effect can be tune by the carby)it should be allright.However your motor doesnt look stock ,so it might have low vacuum already,making the pcv valve not function properly.

[DANNY8]

Might hook it all up and see how it goes on the dyno, do a run with it connected, and a run without, see wat the difference is. Will let ya's know how it goes.

Also it seems the charcoal canister is just connected to vacuum, but has a vacuum solenoid in the line so it doesn't open at idle.

[ari666]

carbon can shouldnt have anything to do with a running engine, all it does is filter out excess fumes from the fuel tank. so there should be no vacuum lines at all connected to it.

[DANNY8]

carbon can shouldnt have anything to do with a running engine, all it does is filter out excess fumes from the fuel tank. so there should be no vacuum lines at all connected to it.

The fumes are suppose to get burnt.

[ari666]

no they are not.

they just go through the carbon and turn into vapour and water.

edit* INFLAMMABLE vapour and water

[DANNY8]

Hmmm.....then why are they hooked up to vacuum?

[Tree cutter]

For the PCV system to work you need to have a hose from one of your rocker covers that runs to underneath your aircleaner. A hose from the other rocker cover has tha PCV valve and runs to the bottom of your carby. When you have high manifold vaccum the PCV valve should be sucked closed but when you are at full throttle with low manifold vaccum there will be a slight vaccum inside your aircleaner which should suck the PCV valve open so any oil vapours are sucked in through the top of your carby from the hose under your aircleaner. I would use the catch can in the hose that runs to the bottom of the aircleaner because it should stop oil getting sucked into the base of your aircleaner which will constantly cover your filter will dirty oil.
I am not sure about the charcoal canister you have to use. Some have a hose that runs to the top of the fuel bowl on the carby to suck vapours away and some get vapours from fuel tank also. The small vacuum hose should go to the base of the carby and only get vacuum when you open the throttle a bit, but there should be no vacuum at idle. Older pre pollution carbys have vacuum at idle where the small vacuum hose connects and later carbys do not have vacuum there at idle. One way is called ported vacuum and the other is non ported vacuum. I cant remember which is which. All that is different is one has the hole drilled so it is above the throttle butterfly so there is no vacuum at idle and the older carbs are drilled so the hole is below the throttle butterfly so you have manifold vacuum at idle.