PCV Question

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mnmopar

mnmopar

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Hi All,

So I got new valve covers and had a stupid question. The engine numbers comes back as an 85 318... Is there a negative imapct on not using the PCV and just plugging the holed in the carb?

Thanks in advance!
 
Not as long as the engine is otherwise vented.
They seem to like to be vented on both covers or they tend to pressurize the case and push oil out of little places they normally would not.
(like the dipstick tube)
 
The ideal setup is just what Ma Mopar designed-a pcv valve in one valve cover and a breather that goes into the air cleaner in the other valve cover.

I learned the hard way if either is stopped up or defective (my new pcv valve was bad AND you couldn't blow thru my new chrome valve cover breather! :wack: ) you will blow oil out the dipstick and all over the engine compartment.

The crazy thing about this was you could rip the car down the road and back and get no oil, but you could drive it easy for 5 miles and get oil everywhere.

This drove me crazy. I had a leakdown test done, compression test, everything I could think of trying to find the problem. I finally remembered it didn't blow oil until AFTER I had installed the new parts. I changed them out and everything was fine.

Dallas
 
I would use the PCV valve in one cover and a breather in the other. Not only does it help with crankcase pressure it helps to evacuate moisture as well.
 
And if you get enough pressure in the crankcase, you can push out the intake end gaskets. Ask me how I know that :D A buddy brought his newly modified small block Demon out to the track one night and made a pass shifting at 6200 and not only did it push the dipstick up, it blew oil everywhere and pushed the end gaskets out too.
 
I had kinda a different experience, I had a bad gromet for the PCV valve. The PCV basically just barely laid in the hole, but it looked like it was fine.. The gromet was so worn and old it was like sponge material. After I had the engine rebuilt it was a natural assumption all those little details were taken care of.. Wrong... "assume" means "***" out of "U" and "Me", which it did. I had a hesitation everytime I did a hard acceleration. It wasn't until I was cleaning on the engine and the PVC valve fell out of the gromet, that I found my reason for hesitation because of engine vacuum. Replaced the gromet, took the car out warmed it up, then promptly stood on it.. Needless to say I was plastered in my seat and no hesitation!(with a huge grin on my face).. So you can go from one extreme to another with engine vacuum.. Just an extra tid-bit for someone in case they too have the same problem..

19..
 
Thanks all,

If I just used a beather in both sides? I just find it weird that there is a PVC in one side and not the other. And yes, I did by two cool breather caps that match the valve covers <sigh>
 
mnmopar said:
Thanks all,

If I just used a beather in both sides? I just find it weird that there is a PVC in one side and not the other. And yes, I did by two cool breather caps that match the valve covers <sigh>
Click to expand...

The PCV valve acts as a vacuum to evacuate crankcase pressure the vent allows a source of air to be sucked in.
 
You need to use a PCV valve! This place is full of posters asking the same question & complaints about chronic oil leaks from their engines. A breather may look cool but it is NOT a way to correctly evacuate combustion gasses from the crankcase. I know everyone thinks their engine's rings are good enough that they don't have any blow by, but they're wrong! Every engine has some amount of blow by & the gasses need to be removed by a negative pressure source. By manifold vacuum or otherwise. The breather is designed to allow air INTO the crankcase at a fixed rate. It cannot adequately vent the crankcase on its own even if you run 2 breathers. Failure to install a PCV valve or other form of crankcase evacuation system will result in seals & gaskets leaking, poor ring seal & condensation buiild up in the engine in places you dont want.
Do yourself a favor & install a PCV valve.
 
<looks for straw>

I get it... At least I'll have and extra breather cap!
 
I have to say I'm not in favor of "open breathers." These will ALWAYS tend (especially if you like to "play" on the on ramps!!!) put a film of oil on the engine, firewall, and may work it's way up onto the windshield as well as causing smell in the car.

I did things a little different. I DO use a PVC valve, but I also got some "twist in" Ferd style breathers with hose fittings for each side, and ran lengths of 5/8 hose down below the engine, "road draft" style. I consider this temporary, when I think of it (on a warm day) I'll put a fitting on my air filter base (Edelbrock) to fit up to the hose.
 
Lonewolf3165 said:
You need to use a PCV valve! This place is full of posters asking the same question & complaints about chronic oil leaks from their engines. A breather may look cool but it is NOT a way to correctly evacuate combustion gasses from the crankcase. I know everyone thinks their engine's rings are good enough that they don't have any blow by, but they're wrong! Every engine has some amount of blow by & the gasses need to be removed by a negative pressure source. By manifold vacuum or otherwise. The breather is designed to allow air INTO the crankcase at a fixed rate. It cannot adequately vent the crankcase on its own even if you run 2 breathers. Failure to install a PCV valve or other form of crankcase evacuation system will result in seals & gaskets leaking, poor ring seal & condensation buiild up in the engine in places you dont want.
Do yourself a favor & install a PCV valve.
Click to expand...
What did we do BEFORE PCV systems? Before the mid 60's, not that many cars were using the PCV system and the engines were just vented to atmosphere via a down tube (draft tube) at the rear of the engine. Diesels were still done that way until recent times. My 97 diesel is vented to atmosphere with a draft tube. However, the PCV system is by far better than the draft tube method and still much better than using two breathers on the valve covers.
 
Cranky said:
What did we do BEFORE PCV systems? Before the mid 60's, not that many cars were using the PCV system and the engines were just vented to atmosphere via a down tube (draft tube).
Click to expand...

Yeh....BUT a draft tube is much different than open breathers throwing oil all over the firewall, and THEY DID ANYWAY!!

I still remember some of those days, and the "local oil burners." You could always tell "Smittys" 50 Chiv wobbling down the road because it had a blue trail enshrouding "the rest of us." And you could "goose" the engine with the hood up and see a puff of oil smoke coming out the breather, adding to the dusty, oily, greasy "stuff' all over everything.
 
Cranky said:
Diesels were still done that way until recent times.
Click to expand...
Diesels have very minimal intake vacuum since no throttle plate. My Mercedes 300D's have a tube from valve cover top to inside the air filter, with no PCV valve. They have a complicated oil recovery "bottle" w/ drain tube to the oil pan. I expect the crankcase runs slighly pressurized since diesels have more blow-by than a gas engine, especially when worn. I have never seen a Mercedes diesel engine that wasn't gunky around the front seal and air cleaner, and nothing is blacker than diesel oil.
 
A PCV, affectionately known as a "Pollution Control Valve", LOL, was designed as a way to recirculate unburned gases. Does it or may it have some benefits in other ways, yes.

A breather works in BOTH directions. Just like your body breathing, it's an in and out operation. You think this engine needs a PCV.

carb001Small.jpg


How many cup cars, sprint/wing cars, pro stock, super stock or stock eliminator cars run PCV's? Don't see many of those pushing out gaskets... They don't run them because it fouls up the intake charge with second hand unburned garbage.

If you don't run a PCV, make sure you have plenty of breather area to sufficiently vent the crankcase.
 
Cup cars get torn down more regularly than my street cars though...

I have run with and without Positive Crankcase Ventilation, breathers throw oil everywhere, eventually clog up with **** and then push the dipstick up and throw more oilmaround. Justuse a PCV.
 
Race engines don't need or want a PCV, typically. Of course, they're rebuilt more often, have better ring seal, and have different operating conditions than street cars. I did see an article in a now-defunct mopar mag where a Super Stock racer with a 340 demon ran two PCVs. LOL

Street cars can use a PCV to reduce stink in the car, help control condensation, and make life easier on the people behind them. LOL

If you've got a lot of blow by, it'll keep everything in the engine compartment from getting a film of oil on it also.

On mine, I run a breather with a filter on it on the driver valve cover instead of screwing with running a hose back to the air cleaner.
 
And how many race cars run pan evac pumps these days? They actually free up some power too.
 
Cranky said:
And how many race cars run pan evac pumps these days? They actually free up some power too.
Click to expand...

Yes, simply stated, that is a sophisticated pcv The pcv don't go a way with a race eng, it just get better!
 
crackedback said:
A PCV, affectionately known as a "Pollution Control Valve", LOL, was designed as a way to recirculate unburned gases. Does it or may it have some benefits in other ways, yes.

.
Click to expand...

P C V stands for positive crankcase ventilation
if you are running the engine on the street its a good piece of smog there in no power loss from this devise because the light spring closes the valve when you go wide open throttle and no air flows. its good for the environment because it helps with hydro carbons but i like cause unburnt fuel in the oil becomes acetic and can etch the bearings especially with modern fuel with alcohol. but it is not needed for your engine to run right or strong. also with a bigger cam it helps with a lean idle circuit if you dont use it. improves idle quality without modifing the carb. it can gunk up intake some if the engine is old with a lot of blow-by.
 
crackedback said:
A PCV, affectionately known as a "Pollution Control Valve", LOL, was designed as a way to recirculate unburned gases. Does it or may it have some benefits in other ways, yes.

A breather works in BOTH directions. Just like your body breathing, it's an in and out operation. You think this engine needs a PCV.

carb001Small.jpg


How many cup cars, sprint/wing cars, pro stock, super stock or stock eliminator cars run PCV's? Don't see many of those pushing out gaskets... They don't run them because it fouls up the intake charge with second hand unburned garbage.

If you don't run a PCV, make sure you have plenty of breather area to sufficiently vent the crankcase.
Click to expand...

No they don't run a pcv valve. But they DO run dry sump oil systems that maintain a negative pressure in the crankcase that help with ring seal (which reduces blow-by) & that helps to evacuate the crankcase gases.
Ordinary breathers don't work in 2 directions, at least not very well because they can't regulate pressure, only vent it after the pressure builds up in the crankcase since there is nothing to create a negative pressure flow. They are designed to allow air to flow inward to the engine.
Even the engine shown needs some sort of evacuation system on it to perform at its best. It doesn't have to be a "PCV valve" system, but some sort of system. A lot of racers use an air pump or check valves on the headers connected to the cranckcase to rid the gases.
 
I guess the sarcasm of the PCV definition and LOL in my post got lost somewhere.

I'll stick with a cleaner intake tract, thank you...

I'm not the one that said you NEED a pcv. People build stuff with different desires and end results. Lots of ways to skin a cat.

The OP should absolutely run a pcv on his engine.
 
Well my assumtion was that it was a street engine w/o elaborate oiling systems. But I did mention there were other methods of evacuation in my 1st post. The op's question referred to any negative affect of just running breathers on the engine. I suggested the PCV valve for simplicity sake.
 
crackedback said:
I guess the sarcasm of the PCV definition and LOL in my post got lost somewhere.

I'll stick with a cleaner intake tract, thank you...

I'm not the one that said you NEED a pcv. People build stuff with different desires and end results. Lots of ways to skin a cat.

The OP should absolutely run a pcv on his engine.
Click to expand...

I looked for the theory of Sarcasm of the PCV and couldn't find any reference to it in my SAE "Theory and Formula" manual. Could you elaborate on it's parameters and how it relates to the reverse velocity of piston speed?

Oh, and to the OP. Run the PCV on one valve cover and a breather on the other.
 
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