i was curious, would hooking the pcv to the ported source work. does the engine need that much ventilation at idle.
i have an open ported manifold source and dont really want to T off of the brake booster port for my PCV

 

It would not perform correctly at idle - important!

It really does need to be full manifold vacuum and larger tube size (volume) so the PCV valve will modulate correctly at idle - pulling the fumes out of the crankcase without creating a huge vacuum leak.

You should not do it.

 

just wondering,
i have seen a lot of posts on here about hooking up the pcv to a holley carb that only has one 3/8 full manifold port. there are many posts and every singlee one says something different. one post says that that the port is for brakes. another post says it is for the pcv. one post says to just T off the large port for both. another says absolutly not.

guess I am going to T off of the port for brakes and pcv then. i read here that this is not a good idea because it will allow gas fumes into your brake booster but how is that possible since it is vacuum and there is a check valve on the booster that only allows air out of the booster not push air in?

i just wish that there wasnt so many answers to the same question. it is really hard for half trained monkeys such as myself to figure stuff out with so many answers to choose from.

 

Most PCV valves send their output to the base of the carb. There may be some that come from the factory going to a fitting on the manifold, but I don't believe any Chevys operate that way. Ported vacuum was used to retard the engine at idle so that it would reduce emissions. Once the throttle is cracked, the port goes to full manifold so that the vacuum can on the distributor can work properly at take-off. I think the oil smoke/etc. in the PCV valve discharge would plug up a ported vacuum passage pretty quickly.

 

Do not T both together. You'll get a reduced vacuum signal to the booster. The only correct way to do this is to drill and tap the manifold for a fitting to hook the brake booster to.

 

You need the PCV to pull full manifold vacuum at idle.

Other than that, it would not be possible to hook the PCV to ported vacuum and make it work, as the ported vacuum ports in the carb are only about .050" in diameter - even when those ports are fully exposed to manifold vacuum there would not be enough flow to ventilate the crankcase under any conditions.

 

I disagree with you all. I'm against getting oil mist fed into the cylinders. Oil builds up in the intake, on the intake valves, cylinders, and spark plugs.

Get rid of All the PVC BS! When a motor makes max blow by and needs crank case ventilation the most is when the throttle is wide open and no vacuum. You are better off with a twin breather system and NO PCV

One other thing is that you have to adjust the carb for a 3/8th vacuum leak that changes with engine vacuum

 

It's PCV (Positive Crankcase Ventilation) not PVC (Polyvinyl chloride).

First, you won't get oil mist in the cylinders if you have the proper baffles in the valve covers.

There are many reasons to run a PCV valve and it's been discussed to death here.

BTW, when I installed a PCV system on my 502, I didn't have to touch the carb. Made no difference at all.

 

Sorry PCV! Now we have a guy who has a hot motor spinning 1000's of rpm that does not create any oil vapor or if it does it's PCV has one of those totally green sub micron filters on it. Give me a break. Here is a very simple test. ON any hot motor with it still running rev it up to 3000 rpm and unscrew the oil filler and then tell me that you don't have oil vapor..... pumping out the hole. Even better yet put that 3/8 line in your mouth and suck on like the carb vacuum pulling 18 inches and tell me if it is good tasting?

You should take a motor apart that has the PCV pumped into one intake manifold runner after 20,000 miles and see the baked on oil in just that one cylinder runner.

We have a state smog test machine in the shop. One of the tricks to pass a car that is failing because of marginally high hydrocarbons is to pull the PCV line off the intake. The straight shot of air without oil vapor will change the PPM on the 2500+ rpm part of the test.

To a simple person a carb runs fine for many years without any changes. I run a dyno at work and we change air bleeds, emulsifiers, jets, mixture screws and evaluate the data from each individual primary pipe and 4-5 other numbers.

A more correct statement is:Idle mixture screws, blah blah blah are factory set to allow for pcv. which is essentially a vacuum leak. So if it is plugged off then you would have to jet somewhat leaner. To achive the exact same A/f ratio under high vacuum cruise conditions.

 

Just a thought - if you're looking at new carbs in the near future one nice feature of the Holley Avenger series is that it has two separate large 3/8 ports for both the PVC and the Power Brake Booster. It also has the smaller ported and unported connections.

 

Wow, this Forum is turning vicious. Just connect the PCV to the carb manifold vacuum and be done with it. I don't question the wisdom of the GM engineers.

 

The PCV valve allows air to flow into the intake at idle... So what?! You adjust the idle mixture for the airflow into the intake; so the air coming in from the PCV valve is part of that [but it is consistent and very predictable]; but that does not mean that you can't set the idle properly. The car will run with or without the PCV valve in the system once it is adjusted properly. The only real difference is that the oil mist which would have gone into the intake and been burned with the fuel charge, is going to go into your engine compartment [via those 'dandy' breathers] and cause you to clean it more often.

 

If you have to use PCV, I vote for what Lars said. The ported should go to the vac advance. The small full vac right next to it should go to the car vac system. ( Lights and dash. ) Under the rear of the carb Should go to the brake booster. In the past before I learned, I even had single planes with rear tapped 3/8th PCV port

Paul67 way to much junk on those stock cars. I have not seen one of those in a long time. :LOL

 

You know that's not the proper way to connect a pcv anyway.



So then you shouldn't have to worry about the max amount of blowby being re-introduced into combustion either.

At full sustained throttle the intake side of the pcv system (passenger cover intake) reverses it's flow and the blowby gases through the pcv intake filter and then thru the air cleaner filter and finally in thru the carb. Not much oil mist gets thru a maintained system.
That is why a lot of higher mileage engines show oil residue there.
Also at full throttle there is usually a couple of inches of vacuum and with the increased blowby crancase pressure it doesn't take much for the pcv to still work a certain amount in conjunction with the passenger side. Remember the pcv valve is metered internally to adjust flow rates too.


It is preferred on a healthy street engine, full blown racing is a different story and there are various methods to extract the vapors and blowby pressures and gain every last ounce of hp. GM and Porsche are still having these problems on their latest engines.


And it will work fine on just one runner too.


In the following pics it shows how usually the 3/8” line is ported for pcv use, evenly to both sides of a divided plenum. Qjets are at the front and most Holleys are at the side towards the rear. Just flip over your carb to trace it. Almost always, the 3/8” line on the base of any carb is for the pcv. Most manifolds have ports in either the runners or the plenum for accessory vacuum supplies and you can tee or use a multiple tap fitting to run the mod valve, booster, headlights, etc from that source, but keep the pcv separate in it’s proper port.

And finally, if you want to resduce the oil mist a little more you can stuff some of this stainless or brass scrubbie into the pcv baffle, available at your local grocery store.

 

Paul67 way to much junk on those stock cars. I have not seen one of those in a long time. :LOL

That's after I removed the TCS!

 

wow
this thread got ugly.

so it looks like my options are

A. drill and tap the intake (which isnt going to happen since it is already installed.

B. Get a street avenger carb that has brake and pcv ports (again a no go since the carb that is on the car is running fine)

C. T off the brake booster line in the back of the carb. Its funny that people are calling that the PCV port when the instructions for the carb specifically call it the brake port. I am thinking that this is the best option since it is a strong vacuum signal and the check valve on the booster will stop any oil mist for somehow miraclously going against the flow of vacuum and getting into the booster.

 

Going to T off of my brake line as well.
I could tap it but I have the same reason, its installed and I dont want to remove it.
What is the difference if I tee it or tap right next to the booster port.

 

I drilled my intake while it was still installed. I took the carb off and stuck the vucuum cleaner hose in the port to the point where I was drilling. I turned it on and let it run during the drilling and tapping process. Took about 15 minutes and it worked perfectly.

I have a 502 with rectangular port heads, so maybe the tiny small block intake ports won't let you do this.

 

I "T" off my Brake port to handle both pvc and brake booster,brakes work fine pvc works fine I have a 383 stroker with a holley on it so thats how I hocked both up.