Wow, some answers have some shaky science behind them. A properly setup PCV system uses engine vacuum to draw fresh air into the cranckase allowing the PCV valve to draw the crankcase vapors into the intake. As Squirrel said, it can either be an open system, drawing air from an external breather, or a closed system where it draws air from the air cleaner. Most manufacturers went to the closed system in the late 60's and it was a nod to emission control not allowing crankcase vapors to vent to the atmosphere. If you have excessive blow-by (more than the PCV valve can handle) the excess would end up being drawn into the carburetor at the air cleaner. Adding extra breathers to the valve covers can negate the scavenging effect of the PCV. You want one inlet far away from the PCV valve to get the system to work most effectively. An air inlet at the front of one valve cover with the PCV and the rear of the other valve cover is a really good setup. Chrysler products of the 70's - 80's had a closed system with the formerly open breater in the valve cover converted to a sealed can with a hose to the air cleaner. These would eventually plug up with time and mileage. The result was an engine with oil seaping out everywhere and probably milky oil on the dipstick, even rust on the dipstick. The fix was replacing the sealed can. These were kept in quantity just under the parts counter along with the dual ballast resistors and the plastic distributor gear for the slant 6.
Jaracer , guess I'm good with (2) breathers & a PCV .One at the front( intake oil fill tube ) , one at the rear (valve cover) & one PCV on other rear side (valve cover like a triangle pattern ) .Should breathe nice.Have a great Day Hambers!
This topic should have it's own "sticky", count the HAMB threads!!! Text version Here: https://www.google.com/search?q=the...UKEwi4pbjl6JmEAxXWGDQIHU8CBP4Q0pQJKAB6BAgAEAc Image version Here: https://www.google.com/search?clien...HYIMDJAQ0pQJegQIDBAB&biw=1280&bih=800&dpr=1.5
you might want to consider that there's more than one purpose for breathers...one is to let out combustion gas that gets past the rings, the other is to remove the "nasty" stuff in this gas, to keep things clean. Having more breathers helps the first, having only one, located opposite the PCV valve, helps the second. Do you care more about how much power you make, controlling oil leaks, or engine longevity? There might be different answers depending on the car and what it's used for.
Every hotrod I own or have owned has had a breather cap on one valve cover, and a PCV valve on the opposite side. I've always been told to never have a breather on the same side as the PCV valve, but always have one on opposite side. Can't imagine where anyone would use 3 breathers mentioned at the beginning of this thread? It's going to cause the PCV valve to not work properly I'd think with 3 breathers.
If the engine has enough blowby that one breather can't handle it, then you probably need another breather. High performance engines might fit this category. Most mild street engines (that are in good condition) don't.
It's NOT 3 breathers .As stated (1) breather on one valve cover & the other valve cover has a PCV valve that ( looks ) like the other breather . Then there is the Oil fill/ breather cap on the oil fill tube on the front on the intake manifold (old school oil fill) . So it's (2) breathers one front ,one pass side & PCV on drivers side ( like a triangle ) Shit I didn't think discussion would go far ,cause I was just being asked " why 3 breathers & like I told em ,its only 2 but I was just throwing it out to you guys for thoughts on is having 2 too many ? Again ,I THANK all for the learning I got from the discussion . I think I'm OK, it's a fresh engine & so far so good ,but I was thinking of getting a more radical set up with different valve covers ( and breathers ) and whether what I had now was correct or not . GRAB A BEER FELLAS ! Weather's getting warmer , time to start pounding the payment, puttin miles on & dealing with problems as the show themselves .
^^^^ I put a used, unknown condition 305 in my truck several years ago set up as you describe. PCV on pass side vc, breather on ds vc and a breather on the oil fill tube. No issues in over 30K miles. It's been a good engine for me. Gary
YEAH IM LEAVING IT & IF I GET ANOTHER ENGINE , GOING SAME WAY.SEAMS GOOD SO FAR . TAKE IT EASY BROTHER & THANKS!
I added a 2nd breather to my 355 recently. I had an issue with it building up too much crankcase pressure forcing oil past the pan and valve cover gaskets. I have to get some miles on it before I can say if it has worked or not.
GOOD LUCK ! Like I said mine is old school intake so I got the PCV & breather towards firewall & front oil fill tube / breather at front of engine so far so good .Have a great day brother!!
Thanks. I've had oil seepage for a while with the car and we were very careful with all the gasket installs. I had some Dart stamped valve covers on it for a while and the gaskets were sucked in at the short ends of the covers. Now I have cast covers with tracks to hold the gaskets. From there I'll revisit my PCV valve placement.
GOOD LUCK ! , Yeah that's why I thought about getting edelbrock finned covers ( because I have aluminum edelbrock heads) .thought the fit would be better , but they only come with one breather on one valve cover & one oil fill on the other valve cover .that would give me (2) oil fills .I don't need that so I'm just painting what I got & letting the breather set up stay as is . Hope it works out for ya , it's a pain chasing oil leaks . Have a good one Bud!
All this talk of " breathers" , if they're on the suction side of the pcv its really an inlet filter . Take a look at what you're using because many don't have adequate filter media to keep the air clean that's entering the engine , some aren't made to filter the air at all , so you're sucking dust , dirt , whatever in to the engine . Most factory setups got their air from inside the air filter housing through a filter media .
We had the one breather problem with my buddy's chevy wagon, sometimes he pulls a vintage camper so he swapped the tired 283 long block with a fresh 400 long block retaining the 283 no hole valve covers and intake to keep the original look, it worked well at slow speeds but when highway cruising the oil fill tube in front breather would mist the engine with oil. Pulled the intake and push rods to install a lifter valley tray to keep most oil off the bottom of intake then drilled and tapped the rear of the intake near the distributor for a heater hose nipple to add a 2nd vent. I did the similar setup on a 400 sbc with 3x2 intake by using a lifter valley tray and adding two nipples on the passenger side front and rear of the manifold, vented both into a header evacuation system, worked very well.
Most factory setups before the late 60s got their air from a breather that was stuffed with metal wool mesh of some kind. But by the late 60s they went to the air cleaner filter on some, or kept the mesh filter in the valve cover, with a hose to the air cleaner housing, but outside of the filter. Good point...sucking dirty air through the crankcase isn't the best thing for an engine, otoh that's how it was done for a long time.
I remember the inline 6 my '49 Chevy pickup had a louver punched in the valve cover. I don't know if it was baffled or filtered. Gary
Well, the HAMB strikes again. Clean air in, suck out the dirty vapes. The end. Draft tubes, the case air going in created by the vacuum from the draft tube was usually filtered thru the oil fill cap. Old days. Later they stuck a fkn Brillo pad gig in the air cleaner housing on the outside of the air filter element and a PCV to suck out the vapes. Racers ran evac tubes in their headers or in extreme cases ran a vacuum pump to maintain case negative atmosphere. It isn't really complicated, props for asking, but we wanna see the NASA spacecraft you're building that needs all this scientific input once it's done.
...along with a host of other things, compared to modern engines. But we won't go there. The fun part is actually driving your car enough to wear out a set of cast iron rings, today
I copied the PCV system from a '66 or '67 Vette 327. The PCV valve screws into the oil filler tube, and the cap on it is sealed. Note: Chevy changed the air flow direction on this, depending on the year. The one I have pulls from the oil tube, and it goes to the base plate on the back carb.. You also need a breather to allow air into the engine. I cut a hole on the bottom rear of the tunnel ram base. I plan to put a vintage air-oil separator on the firewall that feeds into the manifold "intake" port I added. You can see the red tube & small breather here
Mine? I was looking for a good high nickel 4-bolt, which are hard to find nowadays. The date code on my block is 1969. It's got a forged lg journal 327 crank, TRW flat tops. The icing on the cake are the rods. Crower The engine is way too radical for my '59 pickup. It would be better in a T bucket. I think I want to build a 292 or GMC 302 inline to replace it.
Sure there are. I've owned several. But, you seem like some type of armchair expert with your comment
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