pcv = bad vacuum leak?
Le Mans Master
Joined: Apr 2004
Posts: 7,106
Likes: 38
From: Newark DE
between the valve cover and the base of the carb? do you mean having the PCV mounted in the intake itself?
Whereever it's mounted that it works it wouldn't be a vacuum leak as long as the PCV valve is operating correctly. if the PCV goes bad than it can be a vacuum leak.
Whereever it's mounted that it works it wouldn't be a vacuum leak as long as the PCV valve is operating correctly. if the PCV goes bad than it can be a vacuum leak.
Burning Brakes
Joined: Oct 2001
Posts: 1,185
Likes: 0
From: New Wilmington PA
Here's the thing... If you were to clamp off that hose your mix would richen.
If you set the mix with the pcv clamped or removed (and line plugged) and then unclamped/unplugged you would be running lean.
Since the mix is set with the pvc attached and working the bypass air is compensated for.
It is, in a sense, a vacuum leak but the valve limits the airflow to a manageable amount.
If you set the mix with the pcv clamped or removed (and line plugged) and then unclamped/unplugged you would be running lean.
Since the mix is set with the pvc attached and working the bypass air is compensated for.
It is, in a sense, a vacuum leak but the valve limits the airflow to a manageable amount.
Thread Starter
Instructor
Joined: Feb 2005
Posts: 188
Likes: 0
From: Kearney Nebraska
I have it mounted in a valve cover and a breather is mounted in the other valve cover. I have more a little more blow-by on the rebuild than I'd like and the pvc valve doesn't let enough through it. It needs to flow more.
How would it work to attach the tube to the air cleaner instead of the intake vacuum port? This way couldn't I skip a pcv valve and just have a direct hose? Would that work?
In the old days did they use to just run a hose from the valve cover down under the car and let it vent out down there?
How would it work to attach the tube to the air cleaner instead of the intake vacuum port? This way couldn't I skip a pcv valve and just have a direct hose? Would that work?
In the old days did they use to just run a hose from the valve cover down under the car and let it vent out down there?
Burning Brakes
Joined: May 2004
Posts: 1,100
Likes: 3
From: belle plaine ks
It's called a road draft tube
The tube you refer to was on 265 and 283 v-8's. It was the way they used to ventilate the crankcase and balance the pressure to prevent blow by. The reason they quit it is called pollution. Now you recycle the oily gaseous vapor back through the combustion cycle and everybody can breathe better. That's called progress. Considering the number of running automobiles on this planet right now, I'll take progress. I'm not a tree hugger, but low lead gas and positive crankcase ventilation allows you to enjoy a longer life, and to enjoy your corvette just a little longer.
Thread Starter
Instructor
Joined: Feb 2005
Posts: 188
Likes: 0
From: Kearney Nebraska
How would it work to attach the tube to the bottom of the air cleaner instead of the intake vacuum port? This way I skip a pcv valve and just have a direct hose. Would this work and help keep up with the blow-by better than a pcv valve?
Le Mans Master
Joined: Mar 2004
Posts: 7,493
Likes: 1,502
From: Little Rock AR
Here is my suggestion:
Set it up the way GM did.
The aftermarket breather in the opposite valve cover would work in theory but I have experienced oily vapors leaving a mess on the breather side valve cover even with the PCV hose hooked up right on the other side. The solution for me was to run the factory setup where they have an elbow from the valve cover (opposite side from PCV valve) that connects to a small filter element or flame arrestor inside the air cleaner. Solution - The vapors are contained! No more oily mess. Negative pressure helps reduce the vapors blowing out on to the engine from leaky gaskets too.
It is ALL good!
Keep in mind that the PCV system does not pull any air under WOT so it can't be all that bad for performance. It does nothing when you have your foot in it and it keeps your engine clean when you are puttering around the rest of the time. Fight it for yourself if you want but the factory PCV system WORKS VERY WELL.
Smokey Yunick tried to come up with a better design and the best he could come up with was to use a common puke can tied to both valve covers together. Fab one up if you want but it aint pretty. Works fine for a track car but probably not worth tossing the GM stuff for a road car.
JMO.
-Mark.
Set it up the way GM did.
The aftermarket breather in the opposite valve cover would work in theory but I have experienced oily vapors leaving a mess on the breather side valve cover even with the PCV hose hooked up right on the other side. The solution for me was to run the factory setup where they have an elbow from the valve cover (opposite side from PCV valve) that connects to a small filter element or flame arrestor inside the air cleaner. Solution - The vapors are contained! No more oily mess. Negative pressure helps reduce the vapors blowing out on to the engine from leaky gaskets too.
It is ALL good!Keep in mind that the PCV system does not pull any air under WOT so it can't be all that bad for performance. It does nothing when you have your foot in it and it keeps your engine clean when you are puttering around the rest of the time. Fight it for yourself if you want but the factory PCV system WORKS VERY WELL.
Smokey Yunick tried to come up with a better design and the best he could come up with was to use a common puke can tied to both valve covers together. Fab one up if you want but it aint pretty.
Works fine for a track car but probably not worth tossing the GM stuff for a road car.JMO.
-Mark.
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