To vent or not to vent crankcase

[ThunderKart79]

Without a pvc valve there is no venting. To properly vent a crankcase there needs to be a one way valve otherwise you will suck almost just as much back in as you are pushing out. Yes with low compression it does not much mater the higher your compression is the greater your benefits are from properly releasing the pressure from your internals.

 

[Bansil]

They were only used to keep fluids in from leaking out for fire hazards and epa stuff.

 

[Bansil]

Without a pvc valve there is no venting. To properly vent a crankcase there needs to be a one way valve otherwise you will suck almost just as much back in as you are pushing out. Yes with low compression it does not much mater the higher your compression is the greater your benefits are from properly releasing the pressure from your internals.

When I built an 11:1 434ci SB, it was 100% vented to atmosphere...simple filter to control any blow by from making a mess.

 

[OPmini]

Without a pvc valve there is no venting. To properly vent a crankcase there needs to be a one way valve otherwise you will suck almost just as much back in as you are pushing out. Yes with low compression it does not much mater the higher your compression is the greater your benefits are from properly releasing the pressure from your internals.

pvcs are only there to stop oil from leaking and for EPA regulations. Look at early cars before the EPA no pvc valves, open flow no problems

 

[Snaker]

Without a pvc valve there is no venting. To properly vent a crankcase there needs to be a one way valve otherwise you will suck almost just as much back in as you are pushing out. Yes with low compression it does not much mater the higher your compression is the greater your benefits are from properly releasing the pressure from your internals.

Can't agree.
99% of small engines have no PVC. It's open plumbing from the crankcase to the airbox.

The vent is always necessary.
Its due to the changing crankcase cubic area due to the piston going top to bottom.
Maybe a higher compression engine has a bit more due to possible increased blow by, I'm guessing the increase would small if comparing healthy engines.

Different engine designs will have the biggest difference.
A single cyl will have a huge difference due to no balancing.
A parallel twin with 180 placement will have almost nill, just blow by, due to one cyl balancing out the other.
Same with 4,6t,8,etc.
Engines also have a certain amount of reverse flow, air pulsating back in to the crankcase as the effective area gets larger.
Opposing and v's get weird, a engineer could calculate it.

 

[ThunderKart79]

All true valid points so to be a little more specific there is a new train of thought that there is noticeable gains on small engines, if the block can only expel air then it triggers a vacuum like process that allows more force on the crankshaft that is the best I can explain it and yes you have install a good quality one way valve with an engine that 2 grams off of a lifter is a performance gain my point begin every upgrade is noticeable

 

[ThunderKart79]

I wish I could explain it better but from what I have been able to gather up information wise a check valve “ that I call a PVC” helps in the efficiency “ thermal and mechanical “ department I have also been told the biggest gains are seen in high compression single cylinder engines truth be told like the light weight lifters that I previously mentioned it is probably one of the many tricks engine builders use to maximize HP

 

[Bansil]

All good valid points, depending on application...thanks folks,keep info ideas flowing, if we keep it civil as it has been....lots of folks can benefit.

Biggest issue can be terminology......

 

[ThunderKart79]

Amen the more info I gain the faster my boys go I just need to not be lazy when it comes to typing typically I am lucky if I a small fraction of my thoughts end up in my comments

 

[madprofessor]

All good valid points, depending on application...thanks folks,keep info ideas flowing, if we keep it civil as it has been....lots of folks can benefit.

Biggest issue can be terminology......

The terminology is probably only an issue for weird OCD folks like me, and here's what keeps bugging OCD me.............
That "PVC" valve everybody keeps talking about would melt on the engine, because "PVC" is "polyvinyl chloride", like those drain pipes underneath your kitchen sink.
Engines prefer "PCV" valves, because it stands for "positive crankcase ventilation". Steel ball inside them always got stuck with old caked-up oil, and the test for them was just to blow through it both ways. Repairs on them only consisted of a big squirt of "PB Blaster".

 

[Snaker]

The terminology is probably only an issue for weird OCD folks like me, and here's what keeps bugging OCD me.............
That "PVC" valve everybody keeps talking about would melt on the engine, because "PVC" is "polyvinyl chloride", like those drain pipes underneath your kitchen sink.
Engines prefer "PCV" valves, because it stands for "positive crankcase ventilation". Steel ball inside them always got stuck with old caked-up oil, and the test for them was just to blow through it both ways. Repairs on them only consisted of a big squirt of "PB Blaster".

That's funny, I hadn't even noticed the typo and got caught in myself.
I think all commenting are on the same page with automotive and not bathroom products, lol

 

[Bansil]

I never caught it either, those 3 letters have been an auto term since 1984 for me, so brain autocorrected spelling

 

[Denny]

The proper way to check a pcv valve is to shake it and make sure it rattles. You should never put something carcinogenic in you mouth and suck or blow.
How are you going to baffle the inside of the engine to keep the oil out of the vent line is the point I have been trying to make. There is not a lot of room in the crankcase. Not to mention the oil and windage forces.

 

[Bansil]

Well...I'm old, smoked for years(quit 21 years ago), 16 years on tanks in army, 2 tours overseas in sandbox...remember the burning oil wells for 1st tour? Been a machinist for way too many years....putting a pcv in my mouth is least of worries.

Disclaimer YOUNG PEOPLE ON SITE IGNORE EVERYTHING I SAID.....DRUGS ARE BAD...MMMKKAY

 

[Denny]

Bansil, you are around my age. I started to change oil in cars at age 7 ( by my self). At age 10 started doing body work and learning paint. At age 13 I was body working and painting by my self at age 17 I shifted gears and got an apprenticeship at a Buick dealership.
I ate a lot of lead paint and washed it down with alcohol and enjoyed pharmaceuticals. Been clean since 1992, except for the lead in oil that I absorb. Yup, drugs, alcohol and lead are bad. MmmKkaayy!!
A mind is a terrible thing! Oh yea, to waste!

 

[madprofessor]

You remember the late 60's and early 70's ? If you do you weren't really there. I was a genius as a young teenager, tested 160 IQ. After the 70's I've only been just smarter than the average bear, Booboo!
We didn't use acid just to remove chain rust only, and no herbal tea companies would patent our mushroom tea. Headbands, CPO shirts, elephant bell bottoms, water buffalo sandals. Oh, goodness did we have style! BTW: Went 4 years without a haircut. I could tuck my hair into the back of my jeans.
KIDS, don't try this at home. Or at anybody else's home. Or anywhere. Please learn from my mistakes.

 

[madprofessor]

To properly vent a crankcase there needs to be a one way valve otherwise you will suck almost just as much back in as you are pushing out.

On the Predators (the hemi at least) and similar they all already have a PCV built in from the factory. As ThunderKart said, the air moves both out and in, that's what powers pulse pumps.
The factory PCV is on the underside of the valve cover. It's a reed-type valve in a flat brass body, and it opens and closes with every up/down stroke of the piston, exhausting out the fat (3/8" ID ?) black tube right into the airbox. Even a governed one can flap that reed 3,600 times per minute. Or would that be 7,200 times?
So if using that tube's outlet to run a pulse pump, it doesn't work worth spit because it's all one-way exhausted air. On the hemi, facing the valve cover so OHV is right side up, the reed valve occupies about 2/3 of the right hand underside of the valve cover. Any tap you make for more relief must be in the left hand 1/3 space. OP was concerned about getting a NPT fitting into the valve cover, he must have a non-hemi with the very thin stamped steel cover, too thin for NPT. The hemi cover is cast, plenty of metal, so NPT seals perfectly.
A regular V8 motor's good-ole-days PCV valve with the ball bearing in it would never open up on a small engine, there's not enough crankcase air displacement to push that heavy steel ball.