PCV reloaded

O.K. I know what a PCV system does and how.

In the crankcase we have blowby gas, other gases and maybe pressure that needs too be vented right?

The ole draft tube does the job but having unburned gas routed back to the engine may give me some extra miles right? (letting air pollution aspects on the side for now)

My questions:

1. Setup: No pcv/draft tube at all
The blowby generates pressure in the crank case if the engine is sealed well. The weaklest link would be the dip stick - would it pop out first at too much pressure build up?

2. Setup: PCV connected to intake
The valve relases the pressure at low engine vacuum and maybe ****s some unburned hydrocarbon. The air/gases are comming in by the carb and get blowed by the pistons in the crank case. Why would I need an other air intake like a vented cap or breather?

3. Would a extra intake not **** fresh/filtered air throu the whole engine (regardless how much pressure/unburned gases are in the crank case) and would my mixture not lean out because of this extra air?

In "How to build horsepower" the autor says "a PCV system with an Air intake would be useless" but every one I saw is build just that way.

Thanks, Frank

 

I used to say that there is no place on a hot rod for a pcv, and in actuallity this is true, it is merely an emissions device. If the motor is near stock, maybe it's not a big deal, but with an aftermarket intake, hot cam, headers, decent heads, making the motor docile enough to drive on the street is #1. I've always been able to get my rods to idle real nice(stick shift helps a lot) and run clean without a pcv, but my old Monte Carlo/300 horse 350 had one and I left it, did a curve kit and an APO vapor injector and was able, after a lot of tweaking, to run regular pump gas, but that was a factory cam/10:1 compression.

 

On my daily 235 I experimented for a couple of years with variations on a PCV setup, different flow direction, various valves and filters, etc.
In the end, I went back to a road draft tube with the valve cover sealed and a sealed hose connected to a carb air cleaner.

If you go with or without PCV, the crankcase needs venting, as in outlet and filtered inlet.


I found that most of the crankcase vapors are NOT unburnt gases and don't help at all keeping the combustion chambers clean.
The PCV valve spring has to be a certain tension, tuned to your particular engine and manifold vacuum, as PCV is basically a controlled vacuum leak. A condensation filter is a must and needs to be drained a lot, especially in the winter.

The biggest reason for me to NOT go with PCV is that it's useless at high rpm.
Manifold vacuum is almost zero - no PCV suction and the small hose after the PCV valve and the filter restriction just can't keep up with the extra blow-by pressure. Piston travel is harder and oil vapor starts to come out of any opening it can find, as in dip stick tube, dizzy shaft, etc. making a mess.

On the other hand the large diameter original draft tube easily relieves the crankcase pressure and leaves the engine happy and clean inside and out.

High rpm V8s use a different crankcase evacuation system via the exhaust pipe using a regular one-way valve. The exhaust pulls out the crankcase vapors as the rpm increase.


Some say PCV was introduced in the 60s mostly to make law makers look like they care about the environment, but it doesn't really reduce air polution in a measurable way.
At least on the 216/235/261 I found it to not have any advantages at all.

 

A PCV system moves air through the engine taking acid forming gases and moisture with it out of the crank case.

Put a straw in your mouth with your finger over the end and ****. Nothing happens. No air movement. Take your finger off the end and all of a sudden you get air movement. You put a breather element over the end to keep dirt from being ****ed in just like the air filter. To work right, you need air movement through the engine. Anything else is not a PCV system. It's just a pressure relief valve. They are not the same thing.

 

Postive Crankcase Ventilation

means to let clean air into the crankcase, and pull the dirty air out

A big part of blowby is exhaust gas, and a big part of exhaust gas is water vapor. Sounds to me like a good reason to run PCV

 

Lots of water from the burning gas plus various partially burned impurities that can form into acids...the water is a key ingredient in sludge, the acids in bearing damage and general corrosion. I suspect PCV is as important to the oil as your filter. Ineffective at full throttle, but you can only spend a few seconds at full throttle anyway, unless your car is too underpowered to get you into trouble.

 

Than´s for the reply guys, but what I want to know is, if the crankcase pressure comes from blowby the "intake" for the PCV would be the carb.

So why do I need an additional air inlet - just to **** more air in the motor that I have to vent?

 

I am going to make an ***umption that you are talking about your 235. If that is the case, the road draft tube vents the crankcase. that air is replaced through the vented rocker cover cap.

 

If you don't have a clean air inlet to your crankcase, you don't get true ventilation. Only the small positive pressure is relieved but the harmful vapors are always inside your crankcase at all times.

A good crankcase ventilation system will always **** out more vapors than the engine can generate with blowby alone.

The original simple crankcase ventilation draft system (not positive) works regardless of rpm, as the angled cut tip ****s out more vapors with increasing driving speed.

POSITIVE crankcase ventilation - PCV describes a ventilation system that uses manifold vacuum and a flow regulator valve for evacuation - hence the 'positive' designation.


Whatever you end up using, the crankcase outlet needs to get vapors out as fast and easy as possible and the inlet needs to be filtered and allow as much fresh air in as nasty vapors go out.

 

also don't confuse what the race car guys are doing, with what you need to do on a street engine. The race car guys like to run a vacuum in the pan, to improve ring sealing I suppose, possibly some other reasons...anyways, they also change the oil after each race date...so they don't need to worry about what happens when the nasty chemicals formed by the vapors sit in the oil for months at a time

 

O.K. so I go and set it up with an valcover inlet/breather a catch can and a pcv valve.

Any idea what valve to buy for a warmed up 261 inline six?

Thanks, Frank

 

I ended up buying two PCV valves with the weakest springs inside.
With a vacuum gauge you can see which one will drop the least vacuum at idle (max. vacuum).
This will push the plunger inside the valve to it's maximum restriction setting.
As vacuum in the manifold drops, the plunger in the valve also drops and allows more flow.
If you drive with the vacuum gauge connected and inside your cab, you can see exactly when the PCV valve kicks in and how much flow it allows.
Try stronger spring valves to find the setting that gives most PCV flow with least manifold vacuum drop.

It's always fun to experiment like that.
I spent so many hours dialing in the perfect PCV system.
I was pretty happy in the end and the filter took so much **** out of the system it was hard to believe.

After all that I went back to the simple road draft system - it just works better for my 235 and leaves it clean inside and out.
The crusty build up inside the combustion chambers after 2 years of PCV are another reason why I never use it again.

 

For many years, 6 cylinder GMC trucks used a "Donaldson Valve" on the rocker cover piped to the center of the intake manifold, closed system with fresh air drawn thru a filtered intake at the oil fill. It worked well.

 

Some old Model A guys run a pcv, and the oil seep at the rear main seal stops. Think about it.

 

Breather on a PCV system actually breathes both directions depending on the moment.

There's times when the PCV valve is closed, but the engine is still pressurizing the crankcase with blowby, it's a fact of life even with a well sealed engine. During this time, the breather is allowing the crankcase to vent, and blowing air out like a road draft tube would.

When the PCV valve is open, the breather is a reverse function, it's an air filter on the incoming air to the crankcase.

 

That's why you can connect the valve cover to the carb air filter, to prevent oily mess all around a typical valve cover breather.

 

Your carb is ****ing air and fuel mixture into combustion chamber not crankcase or surrounding areas. The PCV vent is ****ing air into the valve cover, head, lifter valley, crankcase areas.

The blowby from wear in various compents such as seals and rings allows that mixture blowbuy to enter the surrounding areas. This is what is being ****ed out with that PVC system fresh air intake which is then ****ed into the baseplate of your carb under certain va*** conditions.


I just had a condition where a 454 with high miles which ran perfect but had too much blow by which was causing a rough idle. It was pulling too much blowby junk into baseplate clogging up the idle screw area. Old timer advised to put a simple $3 fuel filter in the PVC to carb line. Worked great as it collects all the junk but allows the system to work. ****s as it has to be changed every other month. Cheaper than a rebuild.

 

I have to dig out this ole thread again.

Is there any reason, not to skip the whole PCV valve and route the crankcase fumes direct to ported vacuum?

Would make pretty much sense in my book. The more RPM, the more vapors are produced, the more it ****s em out.

It would be perfect related to RPMs, you never had to worry about a sticking valve again and it does not produce a "controlled" vacuum leak.

Anyone did that bevore? Did I miss something?

Thanks, Frank

 

Here's a kit for you:

http://www.wixski.com/index.php?page=shop.browse&category_id=1&option=com_virtuemart&Itemid=1

 

Thank´s for the link, but I already got a tube like that (vintage).
My idea was, not to use a PCV valve at all, cause it thends to stick and does barely work at high RMP, but routing the fumes directly to the ported vacuum.

Frank

 

O.K. I know what a PCV system does and how.

In the crankcase we have blowby gas, other gases and maybe pressure that needs too be vented right?
Right.
In some - if not most - there can be very small oil droplets floating around in the valley.
Part of this is due to the drainback holes, size etc.
My 455 series Buick engine has three really big cast holes and you're looking through the valley at the crank . . . which means controlling the air/oil mix in the big Buicks can be problematic at times.


The ole draft tube does the job but having unburned gas routed back to the engine may give me some extra miles right? (letting air pollution aspects on the side for now)
A guess would be that you'll not see any additional MPG and in fact a tightly controlled dyno run would probably show a very small drop.


My questions:

1. Setup: No pcv/draft tube at all
The blowby generates pressure in the crank case if the engine is sealed well. The weaklest link would be the dip stick - would it pop out first at too much pressure build up?
The dipstick can pop up, but usually happens on the high widning SBCs.
Street running usually has the leaks out of the seals and or pan & rocker gaskets.
A weakest link deal.



2. Setup: PCV connected to intake
The valve relases the pressure at low engine vacuum and maybe ****s some unburned hydrocarbon. The air/gases are comming in by the carb and get blowed by the pistons in the crank case. Why would I need an other air intake like a vented cap or breather?
You need "make-up" air to replace the air pulled out of the crankcase.
Make sure it's well filtered.
Imo, the oil filler/breather caps with horse-hair and the like don't cut it for a filtered air inlet.
You can always find grit and dust inside the filler tube with one of these.
Best to use a sealed cap with bib and run a line/hose for make-up air from sealed cap to an inside the carb air filter area.



3. Would a extra intake not **** fresh/filtered air throu the whole engine (regardless how much pressure/unburned gases are in the crank case) and would my mixture not lean out because of this extra air?
It would be like a vacuum leak if you're running a parallel PCV valve.



In "How to build horsepower" the autor says "a PCV system with an Air intake would be useless" but every one I saw is build just that way.
PCV systems were considered to be a "speed secret" in the 30's, perhaps before that and on into the 40's.

They don't hurt anything and in fact - discounting pollution etc. - they help keep the engine clean as well as keep the oil inside the engine.

Street runners should always use one, done right they impinge very little on the 'clean' engine look and with a little extra thought can be another good looking underhood accessory.



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Ok, here's part of a timing article I wrote:

"I got curious about a comment I heard about manifold and ported vacuum going to zero at WOT (Wide Open Throttle) and ran a little experiment.

The car - 32 roadster - weighs 2400#, engine is an overbored 455 with 462 cid, 9/1 compression ratio, Edelbrock Performer intake, Carter 750 cfm compe***ion carb with electric choke added later and a Crower Compu-Pro #1 cam which has about 262 & 266 degrees advertised duration intake and exhaust with 112 degree lobe centers. It’s a smooth cam and the car when warm idles @ 19" vacuum.
The dash carries a large (2 5/8") S-W vacuum gauge which indicates the same as my vacuum/pressure test gauge.

Advance is 8 degrees initial and all in at about 2600 rpm with a total of 32 degrees. Vacuum advance is about 16 degrees and sourced from Manifold Vacuum (MV).
The car runs very well on 87 octane in summer and winter and does not overheat in traffic.

Firing the car from dead cold and on the elec choke, MV reads 18-19" and idle is around 900-1000 rpm.
Ported Vacuum (PV) read 12" on startup.

Once the engine warmed up, MV reads 18.5 - 19" and PV reads zero at about 500-600 rpm.

Cruise at 40 mph with a light throttle setting on a flat road gives you 18.5 - 19" MV and just about the same on PV.
Rolling the throttle in about half way shows 8 - 10" of vacuum on both MV and PV during light acceleration.

Once at 60 mph MV read 18 - 18.5" vacuum (keep in mind this is a very light car) and PV read
10".
Flooring the throttle at 40 mph or 60 mph brought the MV down to 1" or so and PV to zero.

At idle with a fully warm engine, MV reads 18.5 - 19" and PV reads zero.

The lack of additional timing at idle is what creates an overheating problem in the GM engines.
It takes time to burn the lean idle mixture and additional advance is required to get the process underway early and avoid overheating.
Exactly the same thing (overheating) would happen with the timing severely retarded in an engine under load at a higher rpm level.

There’s a lot of confusion out there about timing, both centrifugal (mechanical advance) and vacuum advance as well as the vacuum sources to use.

The key thing is to realize they are two different systems that work together to give optimum spark advance for a particular condition and key on rpm as well as load.

To my way of thinking perhaps there would be less confusion if the vacuum advance cannister was called the vacuum retard cannister.

I’ve been amazed at the lengths some go to, to cure an overheating problem that can be solved in most cases simply by selecting the correct vacuum source.
Granted, most of my experience has been in cars with small engine bays and many times not the biggest radiator in the world, but I note, the bigger cars have the same amount of timing and overheating problems as the small car guys do and for some reason many car owners avoid doing something as simple as swapping vacuum sources to cure overheating and prefer to throw money at the problem.

As far as spinning up a little experiment, I’m not trying to prove anyone wrong here, just got curious, had some free time and those are the results I came up with.




An additional note; for those of you who live at a higher al***ude than where these tests took place, you’ll find that your vacuum levels at no-load (idle) rpms will read lower.
To the tune of a 1" vacuum loss for every 1000' of al***ude.
The tests took place at 350' al***ude and manifold vacuum at idle read 18.5 - 19".
After moving to Sunny Arizona and ending up at 3300' al***ude the manifold vacuum now reads 15.5".
Highway figures and under load vacuum levels remain the same.




This combined article was written from research on timing figures and real world experience.

You can learn a lot by taking the time to set up some inexpensive instrumentation and taking the time to run a few simple tests.
What you’ll gain is a better understanding as to what’s going on with your engine and gain a small bit of education about the particular thing you’re researching.

Learning from books is one way to do it and there’s nothing quite like taking advantage of what smart, experienced and educated people have done and written down for your educational pleasure.

What I’m talking about is the stubbornness and unwillingness to learn from those who’ve been down the road before us.
It’s amazing sometimes to talk to an individual who thinks factory engineers don’t know much.
Thing to recognize is that factory engineers know a helluva lot more than we do and get into sophisticated areas that the great majority of us know nothing about.

Keep in mind too, factory engineers are constrained by the bean counters, the necessity to build a vehicle that is useful to the majority and seldom are let loose to pursue a dream or even an interesting idea.
When they do get the freedom to investigate particularly interesting areas, the results can be astounding.

The name, "Zora-Arkus Duntov" should ring a bell...."
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Some additional info in the next post....

 

Depending on your PCV setup and the vacuum level in the PCV valve proper along with how you're driving the car, - oil drainback as noted above - you'll have differing results from other cars as well as different results under specific operating conditions with your car.

A little background on my car and a few of the problems I've had.

32 roadster, 462" late Buick engine, T-400, 3.70 Ford nine inch and 30" tall rear tires.

I've been screwing around with the PCV system the last few years.
As well as have had the engine on a smog dyno and other smog check machines.
Every time it was noted how clean it ran according to the smog guys.

What's not reflected here is "real-world-use" . . . as in running down the highway at 65 mph + (legit here in Arizona with it's 75 mph speed limits on most highways).
75 per means 80-85 in the real world and keeping up with traffic is a definite necessity.
Along with that, trucks - as in big rigs - obey the same speed limits and it can be a little disconcerting when these guys p*** and you're looking out the window at spinning lug nuts.
Not a problem, they're pro's and have always treated me well.
And, like my pal says, the guy with the most lugnuts always wins.

Running the 3.70's at 80 mph equals 3300 rpm on the tach.
Not a bad deal, but the engine always showed some oil use on long highway runs.
Along with that, run 3300 rpm for a while and tromp the throttle it dumped out an oil cloud that would have made a crop duster proud.

Tried several things and right now I'm running pretty much the standard smog scheme - as I was before - but now it has a home-made oil/air separator and it helps quite a bit.

Even so, due to the drainback system and not-so-swift oil baffle setup in stock condition it'll still pump oil overboard via the PCV system, but not near as bad as before.

Another thing that helped was swapping to 3.00 diff gears and now the engine runs about 2500 rpm at 80 per.
As well as shows no oil loss in a couple of long distance 75 mph or so runs.


Next up is to incorporate some screens in the drainback system as well as a well baffled PCV source inside the intake.

In case you're wondering, the engine has good compression with the last test showing 155-160# in all cylinders.

This is a street runner as you can see and considerably different in the crank breathing dept from the 1/4 mile cars.

Most times life is easy for them, a couple two or three breathers, maybe a one-way header breather setup and they're in business.


A lot of guys run breathers on the street, but imo that's a mistake.
In almost all cases I've seen there are no provisions for controlling airborne dust and they're ingesting dust directly into the engine.

Along with that, these same engines are sporting a well done carb air filter setup, but if you're letting dust in via the breathers, why bother?

 

WOW! Thanks for the info C9. "Vacuum retard" was the magic word.

Duh! It´s pretty straight forward if you use the right word.

I´m also surprised by the fact, that PV and MV are not that much difference while driving. There goes my idea that PV rises with the RPMs.

I think I go back to the draft tube - keep it simple and have a view hoses less cluttering my engine bay.

Thanks, Frank

 

Would plumbing a road draft tube off the oil pan work on an engine with only a vented oil fill tube?

 

About this pcv valve operation, I've got a 1964 bel air 327 cid. it still has the draft tube, someone has installed a looks to be a inline pcv valve but the ends are threaded and it sits on p***. side half way to carb then connected to manifold vac. I installed a edelbrock alum. intake(performer) and did away with the cast oe intake that had the front oil fill. Then installed some old alum. valve covers one side a breather. I didn't think the valve was working as design and creating a vacuum leak so i took out the valve and ran it to the bottom of my air filter housing behind the air filter. now my breather pukes oil out now, it didn't before. With all this talk about pcv valves I would like to know how to properly setup a pcv valve system, or maybe I do have it right but I just need to put a baffle in the valve cover.

 

i should of stated my question a little better. i just wanted to learn a little more for an older more experienced person about how the draft tube worked and if it can work inconjuction with the pcv valve. I am sorry for bumping up this post and wasting your reading mr. rmt. I will hit the library and old manuals to find my advise

 

Your question was ok.

Maybe this will help to answer it.

 

One more question:

I understand how a PCV valve works, but it seems a bit strange to me.
Why not use ported vacuum, ditch the valve (wich often causes trouble)?

Anyone done that?


Frank

 

Ahhhhhhhhh.. road draft tubes.. The older city guys will remember the black oil stripe down the middle of the freeway lanes.. motorcycle guys hated that **** when the first rain of the season came..

 

Where did you read that?

PCV valves are like spark plugs and points. They have a life span and are usually replaced with a good tune up. The only problem that occurs is when they don't get replaced and gum up after many many thousands of miles which lets water vapor ac***ulate and produce sludge.