PCV Routing to Open Element Air Cleaner Base?

[TheWhiteElephant]

I'm installing a Holley 650 DP and Edelbrock Performer 2101 manifold on my '73 K20 with a 350. Due to the limited vacuum ports on the carb, I'm figuring to route the PCV valve to the fitting on the base of my open element air cleaner. I've read mixed reviews in the 'nets, but is there really a good reason NOT to do this?

[SkinnyG]

One valve cover needs fresh air - you can plumb that on the clean side of the air filter if you want.

One valve cover needs the PCV receiving manifold vacuum - this won't work at the air filter, it needs to be the manifold.

[andrewmp6]

What about a carb spacer?

[TheWhiteElephant]

Originally Posted by SkinnyG

One valve cover needs fresh air - you can plumb that on the clean side of the air filter if you want.

One valve cover needs the PCV receiving manifold vacuum - this won't work at the air filter, it needs to be the manifold.

I have a breather on the passenger side valve cover and want to have the PCV plumbed to a port underneath the air cleaner on the base. There's a port under there for this. Are you saying there won't be proper ventilation like that?

[TheWhiteElephant]

Originally Posted by andrewmp6

What about a carb spacer?

Already have a 1/2 spacer/baseplate, didn't want to add another.

[raceman6135]

Originally Posted by TheWhiteElephant

I have a breather on the passenger side valve cover and want to have the PCV plumbed to a port underneath the air cleaner on the base. There's a port under there for this. Are you saying there won't be proper ventilation like that?

Correct. That is not the proper way to vent it. In your system, if I'm understanding you correctly, you are going to have crankcase vapours and blowby gases travel through the PCV valve to the top of the carburetor inlet, thereby coating the carburetor venturi (throats) with oily air.

Another problem with the way you want to do it is that there is not much vacuum inside the air cleaner housing, so you won't effectively evacuate blowby gases out of the crankcase.

The preferred method is to have the blowby gases re-enter the engine below the carburetor so they do not negatively affect the way the carburetor does its job.

Perhaps a photo will help:



In the photo I linked to, filtred air from the inside of the air cleaner travels through the fitting in the air cleaner base you want to use, through the breather hose and into the crankcase to replace the gases that are pulled out via the PCV valve.

[raceman6135]

Originally Posted by TheWhiteElephant

Already have a 1/2 spacer/baseplate, didn't want to add another.

I think what andrewmp6 was referring to was if you could plumb a fitting into the spacer, like this one from Mr. Gasket:



The PCV hose can be hooked up to the spacer port because you do not have one at the base of the carburetor.

[hotrodder]

Why not use the port on the rear of the intake?

[MikeB]

It was sorta implied above, but the PCV valve needs full manifold vacuum. Vacuum won't be pulled on the crankcase if you connect the PCV valve to the air cleaner.

The hole on the other valve cover is where you draw in fresh air (either through the air cleaner or a filtered breather). So, the air flow path is breather -> crankcase -> PCV valve -> manifold vacuum source.

The entire idea is to suck out corrosive gasses from the crankcase, draw them in the combustion chambers, and burn them.

[TheWhiteElephant]

Originally Posted by raceman6135

Correct. That is not the proper way to vent it. In your system, if I'm understanding you correctly, you are going to have crankcase vapours and blowby gases travel through the PCV valve to the top of the carburetor inlet, thereby coating the carburetor venturi (throats) with oily air.

Another problem with the way you want to do it is that there is not much vacuum inside the air cleaner housing, so you won't effectively evacuate blowby gases out of the crankcase.

The preferred method is to have the blowby gases re-enter the engine below the carburetor so they do not negatively affect the way the carburetor does its job.

Perhaps a photo will help:



In the photo I linked to, filtred air from the inside of the air cleaner travels through the fitting in the air cleaner base you want to use, through the breather hose and into the crankcase to replace the gases that are pulled out via the PCV valve.

Thank you so much for the detailed response and diagram. I am running a Edelbrock Performer dual plane. I researched the open spacer vs. the dual plane spacer (divided in the center like the manifold), and chose the dual plane--it doesn't have a port in it and I don't want to use another spacer. I'm not sure I could plumb a fitting into the one I have.

[TheWhiteElephant]

Originally Posted by hotrodder

Why not use the port on the rear of the intake?

I hadn't given that much thought. I may have to use a "T" from the rear port on the intake. I will be running the transmission vacuum and PCV on there if I do.

The carb has one large port at its baseplate on the rear--this is the one I'll use for the brake booster. The QJet use to have a large port on the rear and one in the front of its baseplate.

[rich weyand]

Agreed with all above about not routing the PCV line to the top of the carb.

Common practice is to T the intake manifold port for the transmission and brake booster, and to run the PCV to the dedicated port on the back of the Holley 650 double pumper.

Keep the oily air away from both the brake booster and transmission lines.