PCV Valve on intake manifold

DoneByDoug · #1 (**permalink**) 04-28-2008, 03:49 PM

If a carburetor doesn't have a PCV inlet, I understand you can go directly from the valve cover into the manifold.

On an RPM Air Gap, I'm assuming that's the front hole on the passenger side of the manifold, and the other hole on the driver's side is for the water temperature fitting?

First, is this correct? Second, what fitting is required to use this manifold PCV inlet?

Lastly, why do some folks use a carb spacer and others don't? I know some have a PCV valve fitting, but I would suspect there are other reasons as well.

Thanks in advance,

Doug

CHANMADD · #2 (**permalink**) 04-28-2008, 04:08 PM

Firstly,I think the hole you are talking about has coolant in it!! It would not be wise to connect a PCV to that!! You will most likely have to drill and tap a hole into the manifold ,and be sure that it does not hit coolant and goes into the crankcase.
A carb spacer first stops perculation, and second by increasing the distance from the throttle plates to the valve you increase torque!!

lovehamr · #3 (**permalink**) 04-28-2008, 06:25 PM

I'll chime in here just because it sounds like there may be some confusion. First, Doug; you are referring to the vacuum side of the PCV system correct? In other words you're looking for a way to hook up your valve cover mounted PCV to the vacuum of the intake manifold. If this is the case I don't think that we need to be drilling through the intake manifold into the crankcase. If any drilling is needed at all then right under the carb, into the plenum area is more than enough. That being said; this should not be needed either. You also asked about carb spacers; assuming that you have the hood clearance for a spacer under the carb then the spacer is definitely the way to go. You'll gain a little plenum area which will help flow in its own right but you'll also have a very convenient place to hook your PVC up to. That's a win/win in my book and a no brainer. I wouldn't go drilling into the intake w/o knowing exactly what you're doing.

JMHO, Steve

olddog · #4 (**permalink**) 04-28-2008, 08:07 PM

My Edelbrock Victor Jr has a threaded hole into #1 and #8 runners. The #8 is plugged and #1 has a temp sensor in it (it is modified for EFI). Either hole could be used for a PCV, but I would much rather the PCV go into the plenum area. A bad PVC going into a single runner would result in a lean cylinder.

DoneByDoug · #5 (**permalink**) 04-29-2008, 06:50 AM

Thanks to all. I realized after I posted I was referencing the water coolant inlets!

I had the same issue with just having the inlet go into the one runner. It would seem to make sense that you'd want the vacuum to feed all cylinders, not just one.

Thanks to all,

Doug

Keithc8 · #6 (**permalink**) 05-01-2008, 09:48 PM

There should be a threaded hole in the intake that goes into one of the runners and this will work fine for the PVC system. You can use a spacer which will also help the power of the engine a little more than likely. There are several different typs of spacers out there for different intakes and applications. We have one that is special made for dual plane intakes. You can drill a hole into the back of the spacer and get the vacuum there for the PVC as well. Make sure that your valve cover has baffling in it so you do not suck oil into the intake manifold and make the engine smoke and use oil. Good luck, Keith

jon@harrison.ne · #7 (**permalink**) 05-02-2008, 11:47 AM

The baffle plate can really affect oil consumption. A plate the width of the cover and 3 or more inches long will increase the air flow area and reduce air velocity as it escapes the cover. This will reduce the atomization of the oil and eliminate oil loss thru the PCV valve.

ou812545 · #8 (**permalink**) 05-02-2008, 02:54 PM

Jon,
I have a strong running 418w stroker that consumes a lot of oil, so you have my attention. Currently I'm not running a PVC. I have baffle plates in both valve covers with breathers.

Any recommendations?

Thanks,
Dan

Slick61 · #9 (**permalink**) 05-02-2008, 03:13 PM

Quote:

Originally Posted by ou812545

Jon,
I have a strong running 418w stroker that consumes a lot of oil, so you have my attention. Currently I'm not running a PVC. I have baffle plates in both valve covers with breathers.

Any recommendations?

Thanks,
Dan

I hear ya... same issue. No consumption for the first 300-500 miles after an oil change, then it increases dramatically. Talked to Jim Grubbs Motorsports last night... he wondered if maybe the head gaskets had collapsed & were sucking oil that way. He suggested pulling the carb & looking inside the intake. Will get more info tomorrow when I drop by his shop.

CHANMADD · #10 (**permalink**) 05-02-2008, 03:14 PM

A PCV makes a big difference (IMO) I used to run valve cover breathers and always had oil all over the place and seemed to use oil. I put a PCV valve and one breather in the valve cover( the baffle under the breather inside the valve cover is very important) and all those problems went away!!

J Persons · #11 (**permalink**) 05-02-2008, 05:44 PM

I modified a Stefs catch can into an air/oil separator and PCV mount. It is connected to the left valve cover via a -10 hose, and the PCV is mounted in the top which is connected to the carb base plate. The right side VC provides a filtered air inlet. The catch can is filled with stainless expanded metal that traps any liquid oil before it gets to the PCV. I don't have any baffles in the valve covers, and the -10 hose will get oil in it, but it doesn't migrate to the PCV. I just pulled the carb off today to install an insulated spacer, and the inside of the intake manifold is as clean as the day I installed it. The air/oil separator has been on for about three years. Here's a photo.