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to PCV or not??

8K views 8 replies 6 participants last post by  raj4851 
#1 ·
I have been running a PCV valve on my car since I got it running. I have plumbed a catch can into the system. It accumulates some oil & I'm wondering if I should just should run a couple of breathers on the valve covers & call it good. I don't race the car, street driven only. Thanks in advance, Rod
 
#2 ·
My 2 cents worth. Keeping your engine free of internal pressure build up is a good thing in many ways. I've never had a problem running a pcv valve but that option negates any breathers for the most part since a pcv valve is made to work with a closed system. One of the good things about a pcv valve is that if you have some blow by it gets sucked in and recirculated through the intake.
 
#3 ·
I hope you have a breather on the opposite side valve cover from the PCV valve! I always run PCV valves, and a breather on the opposite side. Don't want a breather on the same side as the PCV valve or it wont work right. Don't want just a PCV valve and not off side breather too.

PCV systems are indeed closed, but unless you have a tube going to your air cleaner on one side, and PCV on the other, it wont work. SO on most hotrods with open air cleaners it needs one breather.

 
#4 · (Edited)
Great advice guys. Street driven engines should always have a pcv valve. At low rpms the vacuum created is a healthy thing. Crankcase pressure can blow off an oil filler tube breather on a 68 and earlier small block even with a pcv valve. I had to screw it into the tube. My coupe has Moroso evac tubes running to headers but that is overkill for a street driven car.
Just think of crankcase pressure as resistance to the piston compression force downward. Relieving that pressure is always a good thing street and race.

Rod my question to you is why do you need a catch can for oil on the pcv system to the intake or carb? Do you have a baffle on the inside of the valve cover? Oil splashing rockers should not have an open suck tube in the line of fire. Baffles stop squirting oil and saturating the pcv setup you run.
 
#5 ·
i run moon breathers to evac pressure . engines dont leak oil they blow it out. relieve the pressure stop the leak . pcv valves were the first gen smog equipment .
i put the valve in the rear of the intake between the carb and dist . i like no hole valve covers . a pcv alone will not stop blow out leaks. my falcon will have no pcv valve on it.
 
#7 ·
The surprising thing is when OE found out that pcv actually made the engine run better.
 
#6 ·
Breathers will indeed allow the pressure to relieve itself, and without a PCV valve. But just breathers will cause oil list to exit those breathers and end up with an oily mess around the breathers. I recall pre PCV engines I owned and drove having oil film all around the breathers. Those old Chevy engines with the breather tube on the front of the intake always left an oily mess on the top of the engine from the fan blades swirling it around. A PCV valve is one emissions add that actually works and doesn't rob power.
When I put the BBC together in my Falcon I didn't want it to look weird with just one breather, so I installed them on both valve covers, but blocked off the non PCV side so it wont suck air in and defeat the PCV system.
 
#9 ·
Okay, you've convinced me. The oil catch can does catch some oil & I think that's better than for it to go back through the intake. I do have a baffle under my PCV valve and I think it's pretty efficient. I still may want to get my PCV away from the oil just to be sure. Anyway, question answered. Thanks very much, Rod
 
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