Hi

What is the PCV valve for ? The one that dumps the crankshaft fumes back into the intake. It is a check valve, right. But what for ? The pressure in the crankcase is always higher than in the intake, isn't it ?
Is it realy required or can a hose be connected direclty between the valve cover and intake ?
What does PCV stand for ?

Thanks. Gunther

 

Concept of the valve is to keep any backfire ignition from entering the crankcase and igniting fumes...then you would really have a problem.

 

Positive Crankcase Pressure is what I have always thought it stood for.

 

It is Positive Crankcase Ventilation. Back in the good ol days they ran a tube out the back of the engine and crankcase vapors exited out in the atmosphere. The PCV uses manifold vacuum to suck the crankcase vapors back in the engine to foul up your plugs trying to burn it. Oops...I mean to be burnt by the combustion chamber.

A better idea is what Olivier is running on his car. An emission extraction system that burns the vapors in the header collector.
No crud being sucked back in your engine. But if you are using your car like a soccermom (on the street), it won't pass pollution tests with that system.

Dep

 

Hi

Thanks for the quick answeres.
Yes, the ignition story is also what I had in mind, but with having the crankcase ventilated to the intake/carb sucking in fresh air from the air filter would not realy leave a explosible gas mixture in the crankcase, or.
My BB does not have a PCV and this since 1992 at least, probably longer and it did have some bad backfires already. ( worst when I switched 2 ignition wires by mistake. ).
So , just for the health of mind , I should install a PCV, shouldn't I ?

Rgds. Gunther

 

An additional added value of the PVC valve is in keeping the Block cavity at a slight vaccumn when the PVC is connected the the manifold. Less pressure below the piston makes for better ring sealling against the cylinder bore. Better ring seal means increase of HP and Mileage.


Regards,
Heli

 

Isn't that PCP???

 

That would be PCP, very common drug of the 70's and 80's; may be still around today.

 

positive crankcase venilation-or P.C.V. VALVE

 

For a street car I feel a PVC is the best choice. The other choices for crankcase evacuation are really for race only type cars. I had a evacuation panic when I discovered the PVC is really just a controlled vacuum leak. But my Chevy shop manual says my carburetor is calibrated for this and I take it as gospel. The PVC has a tricky design that allows it to control partial open on high engine vacuum (idle) and high flow (full open) at low vacuum (WOT). And the PVC will then seat at no/zero vacuum. Also seats at backfire - like a check valve.
As Dep posted the early cars used just a breather and you could try 2 large filters per valve cover just like the circle track racers use.
The exhaust powered evacuation systems may be great for the race track but have little control/regulation for the street. And the dedicated vacuum pump type systems are expensive and can be complicated. But really the hi hp racers sometimes using only 2 piston rings may need a more effective system. You could run one on the street but your setup will probaly run just fine using only the PVC.
Make shure you have the correct PVC and choose a valve cover hole above a baffle in the valve cover. Connect this to the correct size fitting at the base of the carb - though an intake connection close to carburetor would probaly work.
Good luck. cardo0

 

"PVC" is plastic plumbing pipe sorry dude, I couldn't resist.

 

Im currently running breathers. Is this bad for the engine?

 

No, but you will have the clowns from CA yelling at you...

 

CLOWNS!!!! Hey! This is my real hair.

 

 

IMHO - it's better than running a PCV system... Well - it really depends on your application, but I wouldn't want hot and oily air to get sucked into the engine anyway... Hot air = less power... Oily Air = fouled plugs...
For more radical engines - a PCV system just cannot handle evacuation of pressure that builds up in the engine.. Breathers work fine.. but don't use those restrictive breathers with foam in them and a couple of small holes on the bottom.. Those breathers get soaked with oil and when they are completely soaked - they are very restrictive... The best type of breathers are open preathers with a large filter element...

 

 

Thanks for the advice, im currently running the foam kind that you were talking about, since the ones that have a filter element wouldnt fit the stock valve cover, but now that i got chrome tall style valve covers ill probably go out and buy some