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PCV vs Breather

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PCV vs Breather

Postby xenocide4077 » Tue Dec 02, 2008 10:09 pm

Hi all. I'm finishing up a carbureted Chevy 383 build. This engine is going back into a street car.

I'm running into a problem with the quantity of vacuum ports I have from my carb, and the number of things I wanted to run. I have a brake booster that needs a vacuum port, and I was going to run a PCV valve. However, I'm running and RPM Airgap with a Holley 4150, and don't have hood clearance to add the 1 inch carb spacer to hook up the vacuum port off the manifold, even with a 90 degree adapter (it's going in an 89 IROC).

What are the side effects of not running a PCV valve? Is running two breathers good enough? What are the pros and cons of running 1 breather, one pcv vs two breathers?

Obviously I would like to run the PCV valve, but at the same time, when I get a new hood I can take care of that, but the new hood is not in the cards right now.

Anyway, pros and cons? Any serious side effects either way?
Thanks.
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Postby beth » Wed Dec 03, 2008 2:08 am

The pcv valve is very good at removing moisture and corrosive combustion by products from the oil. With just breathers you will need to change the oil more often and even then there will be sludge buildup. Pcv systems increase engine life.

You can drill and tap the manifold plenum or even the plenum end of a runner for the power brake booster. The pcv connection needs to be in or near the carb. If you use a pcv system the breathers must be filtered or vented inside the air filter. If not you will be sucking dust into the oil.
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Postby xenocide4077 » Wed Dec 03, 2008 10:38 am

Thanks a lot. I guess I will look into tapping one of the runners. Would it be impractical to tap one of the cast in nitrous bosses and run the brake booster off of that?
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Postby PackardV8 » Wed Dec 03, 2008 12:09 pm

Definitely make the effort to run the PCV. The nitrous boss would be ideal, if it has enough meat. Use a fitting with at least 1/2" hose barb to the PCV. On intakes where the bottom side is accessible, tapping the center of the plenum is the way to go. On your Air Gap, you can see the bottom, but can't get there with a tap. :cry:

thnx, jack vines
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Postby mike ramirez racing » Wed Dec 03, 2008 2:34 pm

I don't know how well it works but I've seen guys run a tee fitting off the vac line to the booster and use a see thru filter on the hose to the pcv valve.
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Postby 540 RAT » Wed Dec 03, 2008 3:17 pm

For those who wonder if they SHOULD RUN or NOT RUN a PCV, consider the following:

Old road draft tube setups run on older cars could hardly be said to produce negative crankcase pressure. They are merely bleeding off crankcase pressure like ordinary breathers until you get up enough road speed to produce any delta P at all, and even then it can't be called much suction, more like fresh air being gently drawn in, at best. And high performance Japanese motorcycles that make way more hp per cubic inch than most of our stuff ever will, and that turn more rpm than most of our stuff ever will, for decades used only a single vent tube to simply prevent crankcase pressure from building up. They had no intake vent at all, they just simply couldn't build up any crankcase pressure. There was no ventilation flowing THROUGH the crankcase at all. Though they've changed now in more recent years due to emissions requirements. A PCV system does nothing to really help an engine per se, it really only helps overall emissions, which is why it was originally designed. Without it, blow-by would simply be released into the atmosphere, which has been a big no-no for decades, for cars, and more recently for motorcycles. A lawnmower is another simple example of not having a PCV, the same thing as the older motorcycles just venting to atmosphere. A PCV is also not the main mechanism to get rid of moisture, though air flow can help that somewhat. The main mechanism for removing moisture from inside the engine is hot oil above 212* boiling off the water. That's why numerous short cold running trips are harder on an engine than highway driving, because the short trips don't get the oil up to temp for long enough to boil off the water.

Race engine builders use crankcase vacuum pumps in order to use low tension rings for less drag and that vacuum pump helps those rings stay in contact with the cyl walls to retain cylinder pressure, plus the vacuum reduces windage issues, thus making more hp. They do not use it for crankcase ventilation, they use it for crankcase vacuum - big difference. There can be NO crankcase ventilation flow if a vacuum pump is to work. There can't be any CRANKCASE INTAKE VENT on those setups, because they have to create a suction of around 10 to 15" of vacuum, and there could be no suction if there is an intake vent. If there was an intake vent, they would not be able to create any vacuum at all. Here is a statement from a vacuum system supplier:

"Vacuum leaks in the crankcase, valve covers, distributor base, timing chain cover, oil dipstick, etc. reduce the amount of vacuum you will generate. You can easily check your engine by pressurizing it with air, be careful though, you don't need much to find leaks and you could damage gaskets and seals."

Here they are splitting hairs to prevent any vacuum leaks that would affect how well the vacuum system can work, so its easy to see that an open breather that would allow actual ventilation air flow, would render the vacuum system useless. This is a positive "vacuum" system but NOT a "ventilation" system at all. It's the same sort of thing with a header extraction system, only it is much weaker than a vacuum pump, and this one really only works at higher rpm. It also cannot have any crankcase intake vent or it else it couldn't work either.

Positive crankcase ventilation is not imperative to ring sealing and power production. Rings seal because of combustion pressure getting behind them and forcing them out against the cylinder walls. That's why ring side clearance is important, so that the pressure can get behind the rings to push them out. Race motor pistons often have a series of holes drilled in their tops just behind the rings, precisely for the purpose of getting max pressure behind the rings for optimum sealing.

Most hardcore hotrods and many sportsman race cars just use two breathers to vent the crankcase, and they have run just fine for many many years this way. Those engine's don't typically smoke or use oil either, if they are in reasonable condition. And two ordinary breathers will increase performance somewhat by elimination of the engine sucking spent blowby exhaust gases back into the combustion chamber, that a PCV would provide. A totally fresh mixture makes more hp, so not having a PCV does solve the problem of a PCV diluting the incoming charge. And you don't have to be Warren Johnson to appreciate this, because most hotrodders want to get all they can out of their engines. For anything less than truly hardcore race cars that run vacuum pumps, you also don't need to have a slightly lower pressure on the bottom side of the pistons as provided by a PCV system, to try to help high rpm power. The pressure difference between the very few inches of vacuum from a PCV and atmospheric pressure, is negligible to say the least, when compared to the enormous pressure above the piston. Consider a stout big block hotrod's combustion pressure which would typically be somewhere around 1,200 psi, and that is what pushes the rings out against the cylinder wall as well as pushing the piston down. So, a few inches of vacuum beneath pistons would do nothing compared to that. Not only that, but any teeny tiny gains you might theoretically make when the piston goes down with the aid of a little vacuum, you'd lose when the piston goes back up against that same vacuum. You always have pistons going up, while others are going down, for no net gain with regard to that idea.

So if people do want to run a PCV system, there is nothing wrong with doing that, other than you will lose a bit of performance. Remember, a PCV valve is at its most open position with low vacuum on it, so even with only a little bit of vacuum at WOT (which is an absolute necessity if you are to have any carb signal), you will still be sucking in spent blowby gases and reducing performance somewhat. And for those who don't want to run a PCV system, in order to gain a little extra performance and to simplify things under the hood, there is absolutely nothing wrong with doing that either, other than causing a bit more pollution. And running or not running a PCV system also has nothing to do with engine wear, oil change intervals or sludge build-up. Sludge build-up is a result of infrequent oil changes and/or engines running too cold, thus not boiling off the condensation. So, pick your poison, either ventilation system will get the job done. They are just two different ways of doing things. One makes a little more hp and one is more socially responsible. This stuff is not rocket science……………….
Last edited by 540 RAT on Wed Dec 03, 2008 5:15 pm, edited 2 times in total.
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Postby 540 RAT » Wed Dec 03, 2008 3:29 pm

beth wrote:With just breathers you will need to change the oil more often and even then there will be sludge buildup.

1. That statement is completely false. Breathers have no effect at all on when to change the oil. And sludge build-up, assuming an engine that is not running too cold, is determined only by the quality of oil used and its change interval. Breathers have absolutely nothing to do with sludge.

Pcv systems increase engine life.
2. This statement is also completely false. A PCV system will not extend engine life by even one minute.
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Postby xenocide4077 » Wed Dec 03, 2008 4:17 pm

Thank you very much Rat. That was the type of answer I was looking for. I was under the impression that the PCV valve did provide some ability at keeping the engine oil free of water vapor, but I never considered that keeping the oil temperature above water's boiling point would accomplish the same thing. Seems sort of like a duh now that you mentioned it.

As for everybody else, I think that at some point I will run a pcv valve, but based on the cost of a cowl hood, I think that is going to get put off for a while.

Again, thank you very much Rat.
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Postby beth » Wed Dec 03, 2008 5:15 pm

540 RAT wrote:
beth wrote:With just breathers you will need to change the oil more often and even then there will be sludge buildup.

1. That statement is completely false. Breathers have no effect at all on when to change the oil. And sludge build-up, assuming an engine that is not running too cold, is determined only by the quality of oil used and its change interval. Breathers have absolutely nothing to do with sludge.

Pcv systems increase engine life.
2. This statement is also completely false. A PCV system will not extend engine life by even one minute.




The oil temperature above 212 degrees does boil off the water into water vapor that condensates in the valve covers, breathers and filler caps. We have all seen this white goop. Some vapor will exit at the breathers but the engine will remain full of vaporized water that will return to water after the engine cools. Maybe the condensation is less in mild so cal weather.

The combustion gases combine with the moisture to form acids. Without a pcv valve more of this acid will remain in the oil and it can etch bearings. The moisture, acids and oil will cause sludge over time. No, there will be no sludge build up in a racing engine or even a street/strip engine that is freshened every year. The original question was about a "street car".

A pcv valve system will not reduce engine power. The small opening in the valve will not flow enough at the low vacuum during WOT to affect power at all. The pcv valve is also a check valve that prevents flow to the intake under crankcase positive pressure conditions.
Last edited by beth on Wed Dec 03, 2008 5:23 pm, edited 1 time in total.
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Postby 540 RAT » Wed Dec 03, 2008 5:23 pm

beth wrote:
540 RAT wrote:
beth wrote:With just breathers you will need to change the oil more often and even then there will be sludge buildup.

1. That statement is completely false. Breathers have no effect at all on when to change the oil. And sludge build-up, assuming an engine that is not running too cold, is determined only by the quality of oil used and its change interval. Breathers have absolutely nothing to do with sludge.

Pcv systems increase engine life.
2. This statement is also completely false. A PCV system will not extend engine life by even one minute.




The oil temperature above 212 degrees does boil off the water into water vapor that condensates in the valve covers, breathers and filler caps. We have all seen this white goop. Some vapor will exit at the breathers but the engine will remain full of vaporized water that will return to water after the engine cools. Maybe the condensation is less in mild so cal weather.

The combustion gases combine with the moisture to form acids. Without a pcv valve more of this acid will remain in the oil and it can etch bearings. The moisture, acids and oil will cause sludge over time. No, there will be no sludge build up in a racing engine or even a street/strip engine that is freshened every year.

A pcv valve system will not reduce engine power. The small opening in the valve will not flow enough at the low vacuum during WOT to affect power at all. The pcv valve is also a check valve that prevents flow to the intake under crankcase positive pressure conditions.


Reread what I said above, you seem to be missing some points that are absolute facts. And as for sludge, again, if you change your oil at reasonable intervals, you will not form any sludge, with or without a PCV. As for boiling off condensation, if you get the oil up above 212* for an adequate amount of time, you will get rid of all excess moisture, with or without a PCV. If you don't change oil often enough or don't get the oil hot enough for long enough, then yes you can have sludge issues. But this again, has nothing to do with running or not running a PCV, which was the whole point of this discussion.
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Postby beth » Wed Dec 03, 2008 6:12 pm

Here are a couple of links for those interested in PCV operation.


This from GM of Canada,

Part of the positive crankcase ventilation system, which reroutes crankcase blow-by to the intake manifold and back to the engine, where it's reburned in the cylinders as part of the fuel/air mixture. This cuts emission pollution and increases fuel economy because unburned fuel in the blow-by is consumed the second time around. It also keeps the blow-by and water vapour from fouling the oil in the crankcase, thus reducing the formation of engine sludge.

link

http://74.125.95.132/search?q=cache:iIX ... d=93&gl=us

I learned something new. The PCV system was invented by a Willys engineer in 1943, not for emission control but to eliminate engine damaging crankcase vapors.
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Postby 540 RAT » Wed Dec 03, 2008 7:23 pm

beth wrote:Here are a couple of links for those interested in PCV operation.


This from GM of Canada,

Part of the positive crankcase ventilation system, which reroutes crankcase blow-by to the intake manifold and back to the engine, where it's reburned in the cylinders as part of the fuel/air mixture. This cuts emission pollution and increases fuel economy because unburned fuel in the blow-by is consumed the second time around. It also keeps the blow-by and water vapour from fouling the oil in the crankcase, thus reducing the formation of engine sludge.

link

http://74.125.95.132/search?q=cache:iIX ... d=93&gl=us

I learned something new. The PCV system was invented by a Willys engineer in 1943, not for emission control but to eliminate engine damaging crankcase vapors.


Funny thing about that claim, it just doesn't fit with what happens in reality. You may recall the absolutely huge deal Toyota and Lexus had a few years back with a large number of their engines nationwide being destroyed by sludge. And of course they all had state of the art PCV systems. So your claim about PCV's preventing sludge is proven completely wrong by this. That cost Toyota millions not to mention all kinds of customer ill will. The problem was traced to the unusually long oil change intervals that they had gone to, in an effort to reduce the cost of ownership. That is some measurement that is important to manufacturers for comparison and/or advertising. And here they pushed things to far and shot themselves in the foot. And as I said, every single engine had a modern PCV system. So, do you still want to stick to your claim that PCV's prevent sludge, when it was shown clearly otherwise? You cannot make a case for PCV's being important for engine life, because real world facts do not support that.

I can't speak for whatever problems Willy's may have had way back when, but Hotrods and Racecars have been running "breathers only" for decades without sludge. I myself have had no issues all these years with breathers, and neither have buddies who run only breathers. But then we do change our oil as needed and we do get our oil hot, we don't drive like grandma. And the mainstream OEM's didn't start running PCV's until, what the 60's, a full 20 years after the claimed Willy's deal. Funny thing, they weren't prone to sludge buildup before that either. They only went to it just when emissions concerns started being important. And they also claimed that it was for emissions, just as your reference to GM Canada did, which matches reality. I'd guess some ad geek overstated the thing about sludge without having much technical backup for it. Sure its not a bad idea to have some air flowing through the engine, but as Toyota can tell you, that won't save your bacon when it comes to sludge.

You can believe whatever you want, but the point is, if you are getting sludge with or without a PCV, you are doing something wrong.
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Postby stealth » Wed Dec 03, 2008 10:07 pm

Well I can tell you this, if you do choose to run one put a nice size "puke" tank/catch can in between where you pull vacuum from and the intake.

Every PCV valve equipped engine I've seen gets oil in the intake and makes ugly crusty valves and ports. (Nitrous hates oil contamination...so dont even think about it with one) I don't care for them. Heck, just put an electric vacuum pump on there if you need this system, at lest the oil fumes/vapors won't make a mess inside the intake track.

Just my 2c

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Postby rq375 » Thu Dec 04, 2008 8:54 am

Some of the modular Ford guys are running the small air/oil seperators for air tools. Moroso and Steffs both make more substantial air/oil seperators (intended for vacuum pump systems). Also, air/oil seperators are common (maybe required?) on piston aircraft PCV systems.
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