Do you really need PCV?

[70-500-SE-EXPORT]

Just wondering everyone's opinion on running a PCV valve over a breather. I swapped out the breather for a PCV valve on my 383 and my engine started making a horrible can of marbles noise from the top end I thought was the valvetrain. After going nuts trying to track down the noise I realized it was the PCV valve. The PCV is also technically a small vacuum leak making the engine run a tad leaner right? When I installed it the idle raised and had to be re-adjusted. So I decided to re-install the breather and ditch the PCV. Doesn't a breather serve the same purpose as a PCV but just isn't as environmentally friendly?

[JB400]

An air breather just allows air pressure and oil out of the engine from the blow by, and coats your engine.  The PCV valve just redirects the air and oil back into the engine to be burnt again.  Personally, I'd install a catch can.  You just have to drain the oil out of it every so often.  You get the benefit of an air breather, but without the mess in the engine bay.

[ACUDANUT]

You need a PCV

[70-500-SE-EXPORT]

I thought catch cans were for forced induction cars? My breather isn't really coating my engine with oil.. Im using the stock unsilenced air cleaner that has a 5/8 vent hose from the oil filler...So the breather is technically recirculating the crankcase vapors back into the air cleaner.. I don't see the reason I need to use manifold vacuum to suck even more vapors and feed them through the carb base and gunking it up. Also since the PCV takes vacuum it seems it could reduce its effectiveness of the brake booster.

[A383Wing]

yes, you need a PCV system.....it sucks the vapors and fumes from inside the engine to burn in the combustion chamber. If you didn't have one, all that vapor would turn into gunk and stay inside engine and form sludge. It's there for a reason, leave it alone

[HPP]

Your breather system you have is allowing crank vapors into the air cleaner to be sucked up by the carb. But it produces much less vacuum than a pcv system, so it is dependent upon crank case pressure to push the process.  The purpose of the PCV valve is to allow the idle suction under the throttle plates to forcefully pull those vapors, but will lock its self off if pressure builds enough to create reversion into the crank case.

Many modern cars use catch cans so it isn't exclusive to blow applications.

I don't have a pcv system, but I do have an evacuation system. It isn't emission compliant though. I have a one way valve installed in the header collector that runs a tube up to the valve cover and it pulls the vapors directly into the exhaust, thus preventing them re-entering the combustion process. Its a hold over from its race car days

[Dino]

Sorry to hijack but what's the best way, economically and ecologically, to run this?  I have a 71 dual snorkel setup I'd like to use and I thought the attached hose would run to the pcv with the other valve cover having a breather.  Is that wrong?

[A383Wing]

PCV hose goes to intake vacuum nipple on the front or side of carb (3/8" hose nipple), then to PCV valve in top of valve cover. The other side valve cover must have a way to let air back into engine that PCV is sucking out

[PlainfieldCharger]

  Some form of PCV is a must...or the sludge will be coming...

[AirborneSilva]

I recently put aluminum heads and cam in my small block, I left the PCV off and was just using a breather which was blowing oil out of it that I could smell in the cockpit, after putting the PCV back on problem went away.  I have also thought of putting a catch can on it, I know that the Ram guys (which I'm one), put them on their Hemi's so I will probably do that too...

[firefighter3931]

A PCV is a controlled vacuum leak and emissions thing....nothing more. Oil vapor is rerouted back into the combustion process when using a PCV valve. In the early 60's and before, the breathers were vented to the atmosphere with downdraft hoses aimed at the ground. Obviously not very environmentally friendly 

Personally, I don't use them because sucking oil into the intake tract is not something I want to do to my engine. As long as the engine is tight with good ring seal there should not be excessive crankcase pressure. Breather design comes into play as well. Bottom vented breathers with poor valvecover baffleing are the primary cause for oil misting. A properly designed venting system will not put oil mist all over the engine bay. 



Ron

[MSRacing89]

I run a combo evac and breather system with no PCV.  Makes plenty of vacuum at normal driving rpms. It equalizes above 3500rpm so that crossover's do their work at that point.  I spend some time at higher rev's and lot's of on and off the throttle....works great for me.

[Mebsuta]

Have run with PCV and without in a street driven 383 Road Runner.  I couldn't tell any difference except I noticed condensation in the valve covers without the PCV, so I hooked it back up. 

[Chargen69]

i have a pretty high compression motor in my truck, without the pcv i blew out the oil pan gasket, dont understand that, but with the pcv it didnt do it again

[68X426]

Ron - what's your opinion on using a catch can? (on older Mopar BBs)

Anyone using a can?  How are the connections and routing set up?

[fy469rtse]

Yes Ron answered he like catch cans,
Look for a set that I was looking at , for modern hemi engines and self draining back to engine ?

[terrible one]

Ron - what's your opinion on using a catch can? (on older Mopar BBs)

Anyone using a can?  How are the connections and routing set up?

I'm using the small Moroso catch can. I modified the internal baffling a bit but other than that it's a good product. The bottom knurled part just unscrews so you can dump the nasty froth out (I do it when I change the oil) Nothing special as far as routing goes. I need to make a permanent bracket for it.

[Challenger340]

On a Street Vehicle, a PCV system is a nicety for many reasons, all of which have covered already.

just performance trivia but;
One other thing the PCV System assists, NOT mentioned yet, is 2nd compression ring seal ?
Top Compression Rings are "Positive twist"..... 2nd Rings are "Negative Twist", and any pressure buildup between the 2 rings from leakage through the Top Ring Endgap..... invariably causes the 2nd ring to un-seat and lose seal.
The PCV system helps by maintaining NEGATIVE Crankcase Pressure against the 2nd Ring Endgap slowing the pressure buildup between the ringpacks from the Top ring leakage.

Ever wonder why many Performance Pistons today have that larger "space" machined between the Top and 2nd Ring ? KB ? Wiseco ? an Option on many others ?
That's called an Accumulator Chamber, the idea being the larger "Volume" between the Top and 2nd Rings, takes longer to build pressure between the rings from Top Ring leakage, and thereby assist maintaining 2nd ring seal.

[firefighter3931]

Ron - what's your opinion on using a catch can? (on older Mopar BBs)

Anyone using a can?  How are the connections and routing set up?

I'm using the small Moroso catch can. I modified the internal baffling a bit but other than that it's a good product. The bottom knurled part just unscrews so you can dump the nasty froth out (I do it when I change the oil) Nothing special as far as routing goes. I need to make a permanent bracket for it.

If I were to use a PCV the setup Jackson is using is what I would be using as well. 

On mine, I use a breather stack welded to the valvecover with open element breathers clamped on....works perfectly with zero oil mist anywhere. 



Ron

[68X426]

Thank you for the input. 

[70-500-SE-EXPORT]

Thanks everyone for all the great suggestions and info. While a catch can is great for some applications I agree with Ron and think a better breather system is all I need.

[A383Wing]

and a PCV valve hooked up correctly 

[c00nhunterjoe]

Creating a vaccum in the engine will add horsepower. Seen it on the dyno. Running the 572 supergas motor with open breathers netted 15 hp less then when we ran the belt driven vaccum pump and evac system. Granted a pcv system wont pull those kinds of numbers, it does prove the point that a vaccum is better then pressure.