Is it really necessary?

[Headrope]

Is the pcv valve and hose running from the valve cover to the carb really necessary?
Emissions is not an issue on my '66, so I'm thinking that basically I'm just robbing myself of extra power by venting oil (read: poor fuel) into the carb.
I've got a '68 383 in a '66 Charger.
Thoughts?

[Ghoste]

Interesting question.  I don't know how much power loss there actually is there but since the crankcase has to be evacuated somehow, the alternative is to just dump it into the atmosphere like they did prior to pcv.  Is the power loss sufficient to make it worthwhile to plumb it to air?

[Headrope]

Plumbing it into the air would seem to be easy: just remove the hose. The pcv valve would then become another vent, and would function similar to the vented oil filler cap on the opposite end of the valve cover.
The only consequence would seem to be a little oil on the underside of the hood. I don't show my car ... heck, it'd probably be a great way to measure how much blowby there is. And if I decided to show my car, I could just wipe off the oil and put the hose back on.

[Chryco Psycho]

it will make the oil rings work harder to seal the oil out

[Ghoste]

Why is that Neil?

[Jon Smith]

leave it on you're not losing any power it shouldn't be sucking any significant amount of oil, if anything it will help by lowering crankcase pressure and helping ring seal as Neil said

[Just 6T9 CHGR]

A PCV is a controlled vacuum leak to help the rings no?

[Ghoste]

How does it help ring seal by being controlled though?  Wouldn't a vented crankcase like the older engines have provide the same thing?  I always thought the pcv was just to redirect those vapors into the induction system and provide the crankcase ventilation without releasing the pollutants into the air?

[andy74]

ghoste,i am pretty sure you are correct,but the vaccum created by the pcv not only reduces emissions,it helps seal the rings,by not having atmospheric pressure in the crank case.  in other words,the sucking of the un burned gases lets the rings do a better job of oil control!

[Ghoste]

Well, I see that in the fact that many drag cars have an evacuation line plumbed into the headers but I just wondered if it made a great difference with the average street car from the 60's?

[andy74]

a lot of the dragsters have the plumbing to the exhaust because they use low tension oil rings,those require a greater amount of vaccum to work properly.on the average street car,i dont think we will find much of a power difference,but the pcv system will help the enegine last longer,by burning the polutants out of it,and not leaving shit in the oil,and also by keeping the moisture form the air out of the crank case

[firefighter3931]

PCV is just a form emission control....nothing more. I never run a pcv valve because it puts oil vapor into the combustion chamber and impedes the combustion process, reducing power. Before pcv valves became mandatory the breathers just vented to the atmosphere via hoses aimed at the ground. I just run dual breathers on my engines. There are long stack breathers that will keep oil inside the valvecover instead of spreading it around the engine bay.    You could also run breathers and hoses into a vented catch can and accomplish the same thing.   

Ron

PS. here's a pic of the breather i use. These are going to be mounted on my "old school" M/T valvecovers.  

[Tom_440]

You could also run a clear fuel filter in your PVC hose to trap the oil if you wanted to keep the system...

[Ghoste]

Ron, how much power do you think they cost?

[Headrope]

a lot of the dragsters have the plumbing to the exhaust because they use low tension oil rings,those require a greater amount of vaccum to work properly.on the average street car,i dont think we will find much of a power difference,but the pcv system will help the enegine last longer,by burning the polutants out of it,and not leaving shit in the oil,and also by keeping the moisture form the air out of the crank case

So the crankcase doesn't vent itself? I'm not trying to be argumentative, just seems it would have to vent itself to the valve covers, since the pvc hose only runs to the valve cover.

[Chryco Psycho]

I can tell you this without a pcv or header evac & spilt a 440 inatke valley pan in 2 making 7000 rpm runs at the drag strip , I quickly added a pan evac system to the headers & never bent or split a second intake pan

[is_it_EVER_done?]

PCV is just a form emission control....nothing more.

Actually that's not true. Long before emissions requirements came into effect, cars used "road draft tubes" because they helped keep the fuel and exhaust charges blowby past the rings from contaminating the oil. The road draft tubes were angle cut, and hung down into the airstream so that a vacuum was created as the air moved around the tube (exactly as a race header evacuation system works today). A negative crankcase pressure also helps reduce ring flutter caused by the blowby which builds up in a crankcase that does not have it's internall pressure controlled. This was done for power and longevity long before any emissions requirements were mandated.

As for the question of how much power does it cost? I would like to see someone do a back to back dyno test, as the results would be quite interesting, but I would be willing to bet anything that a PVC system would show a power increase over a non vacuumed system, plus It will live a lot longer, with less maintenance, also.

[firefighter3931]

PCV is just a form emission control....nothing more.

Actually that's not true. Long before emissions requirements came into effect, cars used "road draft tubes" because they helped keep the fuel and exhaust charges blowby past the rings from contaminating the oil. The road draft tubes were angle cut, and hung down into the airstream so that a vacuum was created as the air moved around the tube (exactly as a race header evacuation system works today). A negative crankcase pressure also helps reduce ring flutter caused by the blowby which builds up in a crankcase that does not have it's internall pressure controlled. This was done for power and longevity long before any emissions requirements were mandated.

As for the question of how much power does it cost? I would like to see someone do a back to back dyno test, as the results would be quite interesting, but I would be willing to bet anything that a PVC system would show a power increase over a non vacuumed system, plus It will live a lot longer, with less maintenance, also.

The road draft tubes you're talking about were nothing more than hoses pointed towards the ground. There would be minimal venturi effect from air passing over the end of the tube pulling out the spent gases/fumes. Even the header evac systems pull low vacuum at wot....maybe 2-3 in of vacuum.  

If the engine is properly built, there won't be any ring flutter or blowby. Personally, i refuse to contaminate the combustion chamber with oil vapour. If the valvecovers are properly vented with high flow breathers there won't be any problems. Crankcase needs to vent one way or the other : whether it get's released directly into the atmosphere or recycled back into the engine is inconsequential as long as it gets done. The problem with a pcv setup on a real hot combo is that it has a hard time keeping up at high rpm. Think about it....trying to vent a 440 at 6500 rpm through a 3/8in hose isn't exactly efficient.

Walk around the pits of any dragstrip and look under the hood to see what people are running. I'm pretty sure you won't see too many pcv valve setups on serious street/strip cars.

As for a street setup, ya they work but you're polluting the incoming air/fuel mix with oil vapour. Something to think about.  

Ron

[Ghoste]

I agree with you Ron, we never had much road draft to pull fumes from the vent tube of our old farm tractors.  I believe that at speed a venturi effect would help but not much.  As for needing vacuum to vent the crankcase, I thought the whole problem was high pressure in the crankcase, hence the term "positive carnkcase ventilation".  Is it less a case of the induction pulling vapors into the carb than it is the bottom end of the engine pushing them there?

[Headrope]

Wow. This might be a DC.com first: Ron and Neil disagree on something.

I think Ghoste is on the key question: Is vacuum needed to vent the crankcase, or just to suck the vented crankcase air out of the valve cover and into the carb?

[Steve P.]

Many good points are made here. There are many considerations to go with these points. Mainly, once again it depends on your particular build. Street. Strip. Street/strip. Blower. Emission controlled environment. Show.

I think the drag tube thing went out with vacuum wipers. Higher milage motors without a PCV will leave their mark all over your driveway.. Not to mention stink up the car when the oil starts cooking on the headers..  I guess what I am trying to say is that there is no cookie cutter answer for this question in my humble opinion...

[firefighter3931]

Wow. This might be a DC.com first: Ron and Neil disagree on something.

Actually, if you read Neil's response it states that he went to a header evac system to solve the crankcase pressure issues he was having. I think that the header evac is a better option than a pcv on a hot 440 and i'm sure Neil would agree. The one caution i would make on running this type of system is that they are designed for open headers and not really for the street. The evac system will fill the exhaust pipes with oil vapour and if you're running a chambered muffler, oil will pool in the muffler case. This has been known to cause muffler explosions when the unburnt oil reaches a certain temperature (flashpoint) due to hot exhaust gases. This isn't an issue with a true flow thru design muffler like a Dynomax Ultraflow. I wouldn't run it with a chambered flowmaster, however.

Opinion are allways mixed on this subject and many still swear by the old standby PCV valve. I use one on my daily driver beater truck but then again, that engine rarely sees the high side of 4000 rpm.

Ron

[firefighter3931]

Wow. This might be a DC.com first: Ron and Neil disagree on something.

I think Ghoste is on the key question: Is vacuum needed to vent the crankcase, or just to suck the vented crankcase air out of the valvecover and into the carb ?

You answered your own question: " to suck the vented crankcase air out of the valve cover and into the carb? "

Ron

[Ghoste]

But is it being sucked or pushed into the intake?  And does it really matter anyway?

[Headrope]

Air is sucked from the valve cover into the carb.
If you pull the PVC hose off the carb while the engine is running, and put your thumb over the hole you can feel the vacuum.

[Ghoste]

Yes, that''s true, but if you put your thumb over the hole in the valve cover where the pcv plugs in, you'll feel outward pressure.  (we're getting into semantics I think, whether it sucks or blows, the end result is the same)

[Headrope]

That's exactly why I started this thread: I had the PCV hose off and felt the outward pressure at the valve. The outward pressure seemed to me to be an indication that the crankcase vents itself, so I thought I'd ask.

Ultimately I think the additional vaccum created by the carb may be beneficial, but not necessary as a means of evacuating the crankcase; it's supplemental. By removing the PCV and going with dual breathers I could accomplish the same thing and take advantage of whatever gains in power might be the result of having only air and fuel in the cylinders.

Please feel free to continue the debate. I think the question has been answered.

Thanks everyone for your help.

[my73charger]

Sorry to revive such an old topic, but I am getting rid of my PCV and going to dual breathers.  Ron, is this one sufficient?

[TylerCharger69]

If I may add....I'm not too sure about stock valve covers, but I know that most aftermarket pieces have sheet metal baffles that can be mounted inside of the valve cover to help prevent oil from making a mess.  But it seems to me, that somewhere between the valve cover and the carb should be a filter to keep oil from being sucked into the carb itself which is why a lot of people just use pcv filters on the cover instead of the pcv valve to the carb

[elacruze]

Crankcase pressure has an significant effect on engines-but only at high RPMs. A couple reasons;

There is always some amount of energy wasted by the pistons pushing crankcase air around. In fact, your 2-cycle dirt bike operates using crankcase pressure to move the fuel/air charge into the cylinder. So in a 4-cycle engine, making this movement easier or operating at lower pressure translates directly to horsepower. Crankcase volume to displacement ratio is one metric for figuring pumping losses.

Additionally, at high RPM oil tends to stick to the crankshaft in a wind vortex. Eliminate or reduce the amount of air in the crankcase, reduce crank windage and oil aeration.

The Pro-Mod guys with enormous engine displacement use crankcase pumps which are large and use a lot of power to operate. Why?

As far as oil in the combustion chambers, it's never a 'good' thing, but cruising around town the amount that passes through a PCV system is insignificant. If you were going to the track, you'd want to disconnect it and get some more adequate vacuum producing system in place. Rule of thumb is the longer your stroke, the higher your RPM, the more you need crankcase vacuum. Oil reduces the Octane of gasoline, so any time you're near detonation it can be the straw that breaks the camel's back. Oil also produces ash which coats your nice smooth combustion chambers, valves, and ports.

Lastly, how many of us have any idea how good our ring seal is? How many of us know how much oil gets up through the cylinder? Through the intake valve seal? The PCV isn't the major culprit in unfresh engines.

Ultimately a PCV system is good for the environment and keeps oil off your headers, but it does not have the capacity for evacuating effectively during anything more than casual street driving. Personally, I'll incorporate a PCV system in my touring version next summer though it will be of higher capacity than stock. 

[Purple440]

Thanks for bumping this one elacruze, I hadn't seen it.  I was recently thinking that my PVC hose was just bringing in hot dirty air into my carb and am thinking of capping it and putting an air cleaner on like I have on my passenger side. 

Any reason not to?

- Doug

[elacruze]

Thanks for bumping this one elacruze, I hadn't seen it.  I was recently thinking that my PVC hose was just bringing in hot dirty air into my carb and am thinking of capping it and putting an air cleaner on like I have on my passenger side. 

Any reason not to?

- Doug

Well...no.

Any argument in favor of a PCV setup is largely academic, the benefit being pretty much limited to environmental concerns.
Valve cover breathers and a premium windage tray are best for power, PCV for high-vacuum cruising.
I'd have breathers on both valve covers. Not so much a problem anymore, but in the pre-synthetic oil days, paraffin base stock oils were famous for leaving a thick coating of nastiness inside the valve covers due to the relatively cool covers condensing the mist. Breathers help that mist make it out of the engine.

[firefighter3931]

Any argument in favor of a PCV setup is largely academic, the benefit being pretty much limited to environmental concerns.

My thoughts exactly 

Valve cover breathers and a premium windage tray are best for power, PCV for high-vacuum cruising.
I'd have breathers on both valve covers. 

Yep 


Dang....this is an old thread, LOL ! 



Ron

[firefighter3931]

Sorry to revive such an old topic, but I am getting rid of my PCV and going to dual breathers.  Ron, is this one sufficient?

Yep that will work but personally I prefer the taller stack style breathers which allow for drainback. The lower style breathers are vented underneath and will oil mist your engine under hard acceleration. 

Here's what i have on the Black Pig.



Ron

[my73charger]

Thanks guys!   

[1974dodgecharger]

wow, old thread, but im assuming RON you still run both breathers still?

I did a search on breathers becasue I have mine plumbed under the air intake system and now reading further oil gets pushed through the pcv now I dont want it in my air pan now gheeez.

I think im gonna get me another air breather for the other side.....

[jlatessa]

Here's something to consider, I purchased a Steeda Oil Separator Kit from a Mustang supplier,
it operates the same way an air compressor oiler works, but in reverse.

You plumb it in between your PCV valve and the intake manifold and it precipitates the oil vapor
and collects it in a clear plastic bowl that has a push valve at the bottom for emptying.

They sell two sizes, (I bought the small one) but haven't installed it yet.
It seemed to me a good solution to fume evacuation and yet not screwing up your
combustion process.

Joe

[myk]

Here's something to consider, I purchased a Steeda Oil Separator Kit from a Mustang supplier,
it operates the same way an air compressor oiler works, but in reverse.

You plumb it in between your PCV valve and the intake manifold and it precipitates the oil vapor
and collects it in a clear plastic bowl that has a push valve at the bottom for emptying.

They sell two sizes, (I bought the small one) but haven't installed it yet.
It seemed to me a good solution to fume evacuation and yet not screwing up your
combustion process.

Joe

Pricey bastards, aren't they?

http://www.latemodelrestoration.com/item/ST-5553710/1979-04-Mustang-Oil-Seperator-Kit?utm_source=google-shopping&utm_medium=comparison-shopping&utm_campaign=google-shopping-v2&year=2000&gclid=CImhv_PmwrwCFYqPfgodGDEArA

[jlatessa]

I'll say...no bargains anywhere these days, but it looks well made.
I plan on using it for street driving and using the header collector
evac system for the track.

Joe

[myk]

I'll say...no bargains anywhere these days, but it looks well made.
I plan on using it for street driving and using the header collector
evac system for the track.

Joe

Oh the system definitely has its worth, for sure.  I think I remember on an 'LS1 forum they had home-made ones going on...

[firefighter3931]

wow, old thread, but im assuming RON you still run both breathers still?

Yep, same valvecovers and breathers that were on the old 446 are now on the 572....still working fine. 



Ron

[Mebsuta]

Ultimately a PCV system is good for the environment and keeps oil off your headers, but it does not have the capacity for evacuating effectively during anything more than casual street driving. Personally, I'll incorporate a PCV system in my touring version next summer though it will be of higher capacity than stock. 

I agree.  PCV is closed and not even working at WOT when there is no manifold vacuum, unless you are using fixed orifice valve.  I use it because I am a casual street driver. 

[1974dodgecharger]

As cooter would say I have a hard time believing you guys are casual drivers.  You guys never nail it when your out?  Never mash the peddle at all?  I mash my peddle even on the highway downshift to 3rd and go away to get away from folks who cant drive. 

Even if you do casual driving why even have the PCV anyways when its only for the environment only?  If one cared about the environment then theres the honda civics out there that get great gas mileage.

[Mebsuta]

As cooter would say I have a hard time believing you guys are casual drivers.  You guys never nail it when your out?  Never mash the peddle at all?  I mash my peddle even on the highway downshift to 3rd and go away to get away from folks who cant drive. 

Even if you do casual driving why even have the PCV anyways when its only for the environment only?  If one cared about the environment then theres the honda civics out there that get great gas mileage.

Casual meaning I don't know how much hp my old RR makes on a dyno, don't know what the 1/4 mile ET is, and don't care.  I will mash it when the coast is clear, but I'm not a street racer either and I don't cruise the burger stand.     

[1974dodgecharger]

but you do mash it so PCV is for?

Im curious now why have the PCV if its just for environment and it is only operarting at near idle and light cruises.

endless debate I guess....Ill stop there. 

As cooter would say I have a hard time believing you guys are casual drivers.  You guys never nail it when your out?  Never mash the peddle at all?  I mash my peddle even on the highway downshift to 3rd and go away to get away from folks who cant drive. 

Even if you do casual driving why even have the PCV anyways when its only for the environment only?  If one cared about the environment then theres the honda civics out there that get great gas mileage.

Casual meaning I don't know how much hp my old RR makes on a dyno, don't know what the 1/4 mile ET is, and don't care.  I will mash it when the coast is clear, but I'm not a street racer either and I don't cruise the burger stand.     

[Mebsuta]

If you get in your car and run some errands and go places, you will spend a lot of your time idling or at part throttle.

I can't drive to the post office or Walmart with the accelerator flat on the floor the whole time.