Yup Another PCV Discussion

[Kern Dog]

I recall the stories of cars before the PCV systems were implemented.
Ever heard of a Road Draft Tube ?
This was a crude system that had a section of pipe attached somewhere on the engine that ran down underneath it. When driving down the road, a vacuum formed to pull vapors out of the crankcase and just dump them into the air. Worn out cars looked like crop dusters going down the road. I don’t know much about them except what I have read. This is one of those antique relics that I shake my head at…. Like a 15 year old kid today looking at a rotary phone.

 

[moparedtn]

What is a PCV valve and how does it work?
The purpose of PCV valves isn't just for environmental control....
Besides, engineers at Chrysler who know a damn sight more than I do about the subject
decided it was best to have one on the engine. Good enough for me.

 

[toolmanmike]

I recall the stories of cars before the PCV systems were implemented.
Ever heard of a Road Draft Tube ?

Ya, in post #10

 

[toolmanmike]

Here's am explanation from Slantsixdan explaining the system, how it works and the history.

" PCV became mandatory in California for '61, in New York for '62, and was standard equipment in all states + Canada for '63.

The purpose of the crankcase ventilation system (of whatever type) is to take vapours and fumes out of the crankcase, so there has to be an air inlet; it’s called the crankcase breather. Air flows in through the breather, sweeps crankcase fumes and vapours along with it, and out via one method or another. The out-via method is what began to change in California in 1961.

What was mandated on new ’61 cars in California (and ’62 in New York, and became standard equipment on more or less all vehicles for ’63) was positive crankcase ventilation: crankcase gases had to be ducted into the intake tract rather than dumped out into the atmosphere via a road draft tube. It was not a closed system, because the crankcase breather was still vented to atmosphere. But it was widely, sometimes even officially, and erroneously called “closed crankcase ventilation” at the time.

With an open-to-atmosphere breather, under zero-vacuum conditions (wide open throttle, e.g. up a long hill) and/or on an engine with high blowby volume, the crankcase gases flow right back out through the breather, i.e., the system reverts to a basic direct-vent mode. This causes objectionable odours in the passenger compartment, and releases unburnt hydrocarbons into the atmosphere, where they create photochemical smog.

So, starting in 1964 in California and 1968 nationwide, the (truly) closed positive crankcase ventilation system was introduced. On this system, the breather is ducted via a hose to the air cleaner. Most of the time, this is just exactly the same as venting to the atmosphere: air flows into the crankcase through the breather (which contains mesh to keep the spiders out of the crankcase), and out via the PCV valve. But under those low/no vacuum and high-blowby conditions when an open system just vents off into the atmosphere, there’s still suction above the throttle plate due to the influx of air through the air cleaner and into the carb, so the crankcase gases are still drawn off out of the crankcase and consumed in the engine.

The closed system constitutes an improvement, but in extreme conditions, high volume crankcase gasflow out of the breather can oil down and ruin an air filter element. Heavy-duty vehicles sometimes had a foam or gauze wrapper around the dry air filter element to stave off filter wetdown (until the wrapper disintegrated or got thrown out and not replaced). Obviously not a problem with oil bath air cleaners. "

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[pnora]

Here's am explanation from Slantsixdan explaining the system, how it works and the history.

" PCV became mandatory in California for '61, in New York for '62, and was standard equipment in all states + Canada for '63.

The purpose of the crankcase ventilation system (of whatever type) is to take vapours and fumes out of the crankcase, so there has to be an air inlet; it’s called the crankcase breather. Air flows in through the breather, sweeps crankcase fumes and vapours along with it, and out via one method or another. The out-via method is what began to change in California in 1961.

What was mandated on new ’61 cars in California (and ’62 in New York, and became standard equipment on more or less all vehicles for ’63) was positive crankcase ventilation: crankcase gases had to be ducted into the intake tract rather than dumped out into the atmosphere via a road draft tube. It was not a closed system, because the crankcase breather was still vented to atmosphere. But it was widely, sometimes even officially, and erroneously called “closed crankcase ventilation” at the time.

With an open-to-atmosphere breather, under zero-vacuum conditions (wide open throttle, e.g. up a long hill) and/or on an engine with high blowby volume, the crankcase gases flow right back out through the breather, i.e., the system reverts to a basic direct-vent mode. This causes objectionable odours in the passenger compartment, and releases unburnt hydrocarbons into the atmosphere, where they create photochemical smog.

So, starting in 1964 in California and 1968 nationwide, the (truly) closed positive crankcase ventilation system was introduced. On this system, the breather is ducted via a hose to the air cleaner. Most of the time, this is just exactly the same as venting to the atmosphere: air flows into the crankcase through the breather (which contains mesh to keep the spiders out of the crankcase), and out via the PCV valve. But under those low/no vacuum and high-blowby conditions when an open system just vents off into the atmosphere, there’s still suction above the throttle plate due to the influx of air through the air cleaner and into the carb, so the crankcase gases are still drawn off out of the crankcase and consumed in the engine.

The closed system constitutes an improvement, but in extreme conditions, high volume crankcase gasflow out of the breather can oil down and ruin an air filter element. Heavy-duty vehicles sometimes had a foam or gauze wrapper around the dry air filter element to stave off filter wetdown (until the wrapper disintegrated or got thrown out and not replaced). Obviously not a problem with oil bath air cleaners. "

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Why do you post information like this when it is true and factual?

 

[toolmanmike]

Why do you post information like this when it is true and factual?

I like to teach or at least put the false information back on the shelf.

 

[moparedtn]

Why do you post information like this when it is true and factual?

 

[Moparfiend]

Well if the government and @pnora thinks it’s right thats good enough for me. No need to discuss this any further then .

 

[Kern Dog]

Let’s leave Government out of it !

 

[pnora]

Well if the government and @pnora thinks it’s right thats good enough for me. No need to discuss this any further then .

I think you got tooled by the tool man.

 

[Moparfiend]

Sooooo I was wondering if there is any downfall in using a vacuum canister connected to the manifold then out to the brake booster AND the PCV with proper check valves in line. Would this help alleviate the concern that folks have when using a T from a single manifold source (ie from the source to the brake booster and PCV?

 

[Geoff 2]

Post #3 says it all.
You talk about the 'contaminants' being drawn into the engine. The contaminants [ combustion by-products ] are in the engine whether you use PCV or not.
PCV use started around 1960....still used on modern cars. That is how effective it is.
The engine idles roughly on about 20 cfm of air & 3 cfm comes from the PCV. Nobody has mentioned this: the carbs used on these engines have their idle ccts [ air bleed size, jet size etc ] based on PCV adding idle air. Deleting PCV would probably require some alternative method of making up for the missing PCV air [ such as drilling the T/blades ].

 

[Wietse]

Just the fact that all the toxic gasses from the crankcase are re-routed to be burned in the engine instead of you inhaling them is enough reason to use a PCV i think.

The complain about all the greasy/oily substance contaminating the intake could be an indication there is excessive blow-by going on and engine could be due for overhaul. If an engine is healthy there would not be much crap passing.
Also consider moisture, if this is not properly vented out the crankcase it will contaminate your engine oil which leads to poor lubrication performance and corrosion.

Sooooo I was wondering if there is any downfall in using a vacuum canister connected to the manifold then out to the brake booster AND the PCV with proper check valves in line. Would this help alleviate the concern that folks have when using a T from a single manifold source (ie from the source to the brake booster and PCV?

Many intake manifolds would have a vacuum port that may be used for the brake booster, the carb should have a port for connecting the PCV.
It is not ideal having both Tee in together and adding a canister could help if your engine has good vacuum.
Double check if you have any option to connect it on the intake manifold. If really desperate you could drill and tap a hole in the intake at a convenient location and install a hose barb fitting.

 

[Moparfiend]

Post #3 says it all.
You talk about the 'contaminants' being drawn into the engine. The contaminants [ combustion by-products ] are in the engine whether you use PCV or not.
PCV use started around 1960....still used on modern cars. That is how effective it is.
The engine idles roughly on about 20 cfm of air & 3 cfm comes from the PCV. Nobody has mentioned this: the carbs used on these engines have their idle ccts [ air bleed size, jet size etc ] based on PCV adding idle air. Deleting PCV would probably require some alternative method of making up for the missing PCV air [ such as drilling the T/blades ].

Excellent input regarding the PCV offset to the carburetor! I didn’t think of that! Thats very insightful! Is the PVC source on the carb the same as in the manifold?

 

[steve340]

Run the PCV and brake booster to separate vacuum sources.
You don't want any of that contaminant/oily crap in your brake booster.
You might need the brakes to work properly at some point.

 

[Moparfiend]

Run the PCV and brake booster to separate vacuum sources.
You don't want any of that contaminant/oily crap in your brake booster.
You might need the brakes to work properly at some point.

Makes sense! Is that the only issue from using the same source or is there a pressure issue as well with sharing?

 

[Geoff 2]

As Steve 340 said, keep the PCV as a dedicated port. While usually the carb base is where the PCV port is, some engines run PCV from the PCV valve to a fitting in the intake manifold.

All other vacuum ports for vac adv, brake booster, headlight door actuator etc can be connected together.

 

[steve340]

No the source vacuum and the reading would be the same.
The idea of running the PCV off the bottom of the carb is to share as much of the PCV contaminant across as many cylinders as possible.

 

[Moparfiend]

No the source vacuum and the reading would be the same.
The idea of running the PCV off the bottom of the carb is to share as much of the PCV contaminant across as many cylinders as possible.

Got it thank you!