Hot Rod Forum banner

1 - 20 of 26 Posts

·
Registered
Joined
·
35 Posts
Discussion Starter #1
I have a SBC 383 in a '66 Nova SS that should make right around 425-450 HP so I'll no doubt put my foot into it now and again. So given that info, what are the pros and cons of the different types of valve cover breathers? I've heard that some that "push in" tend to pop out and leak oil under hard acceleration etc etc. I have the cast aluminum Bowtie valve covers that have no holes in them right now. So I don't want to screw them up with the wrong application. Your help and comments are appreciated.
 

·
Member# 3287
Joined
·
2,625 Posts
I've run the push-in style breathers on both my 383 and 406 without a problem. The air should be going in not out. If the breather is pushed out, I'd say that is some other problem.
 

·
Buick Hybrid Guy.
Joined
·
255 Posts
onovakind67 Use a PCV valve on one side and a baffled breather on the other.
Exactly what I was going to say...

With no PCV your going to leave all that blow-by inside the engine. Alot of guys get in trouble by not using that. 1/4mi at a time... proably not a big deal but if your going to street drive I'd put in a PCV on one side and vent on the other.

On the PCV side.. make sure it's not going to be sucking oil vapors. Baffle it inside the cover so it's not exposed to splashing oil. I like to put it on the back side of the valve cover faceing the fire wall and on the inside of the cover epoxy a allum. peice to seperate the pcv from oil splash. Plus your not having to look at it back there since it normaly go's to the back of the carb for vaccume anyway.
The vent should be ok with out a baffle inside but it never hurts!
Hope that helps,
Scott!
 

·
Registered
Joined
·
35 Posts
Discussion Starter #6
valve cover breathers

Thanks for all the comments. Never knew that air flowed "into" instead of out the breather. I always thought the breather was a vent of sorts. Just shows to go ya. Thanks to all esp. Mustang Sally.
 

·
Buick Hybrid Guy.
Joined
·
255 Posts
The PCV should attatch to the intake or the carb and get constant vaccume. That pulls fresh air from the other valve cover along with the gases that get past the rings called blow-by. With out a PCV system your oil will become diluted with contaminates quickly. Moisture has a hard time getting out with no fresh air clearing out the inside of the engine.
~Scott
 

·
Race it, Don't rice it!
Joined
·
7,634 Posts
PCv won't pull vapors out of the engine at WOT because there is no vacuum. The increased combustion pressures force more than normal gasses into the crank case. It's been to be enough to push them out and even create oil leaks. If your rings are in good shape this shall not be an issue.
 

·
Buick Hybrid Guy.
Joined
·
255 Posts
johnsongrass1 PCv won't pull vapors out of the engine at WOT because there is no vacuum.
I agree the PCV has little effect at WOT. Since we are only at WOT for seconds at a time... 11 or less.. it's realy working to the advantage of the engine most of the time.
On serious HP engines they use a vaccume pump which puts a negitive pressure in the crank case that helps the rings keep seated.
There is still no piston driven engine that does not have some blow-by.
Good point about keeping oil leaks from happening.. PCV helps with that too. I'd forgotten about that~
Scott
 

·
Registered
Joined
·
229 Posts
Can someone explain how a vented engine can produce enough crank case pressure to overcome the checkball/spring in the PVC valve? It just seems the one open breather will let the pressure out disallowing the PVC from opening.
 

·
Buick Hybrid Guy.
Joined
·
255 Posts
Elevinpointsixtoone Can someone explain how a vented engine can produce enough crank case pressure to overcome the checkball/spring in the PVC valve? It just seems the one open breather will let the pressure out disallowing the PVC from opening.
The PCV valve should be hooked up to a source that has vaccume at idle. The Carb should have a port for that, if not then you'll need a spacer that has one built into it. (or drill and tap the spacer for it)

That way, there is air being pulled through the vaccume line opening the PCV valve and pulling fresh air into the crankcase all the time except for WOT.
At WOT there is little vaccume to help.

Most of the stuff I deal with is turbo charged. The PCV also is a one way valve that won't let boost back into the valve cover when boost is applied to it... only vaccume can allow it to operate.

Hope that explains it well enough for ya.
Scott~
 

·
Registered
Joined
·
229 Posts
It does explain it if the PCV valve is installed so that the the check ball can be sucked open...I was under impression that the check ball had to be pushed open from crank case pressue and it would "burp" so to speak into the waiting vacume supplied by the carb. If the carb is allowed to pull the valve open with vac all the time (othe than WFO) then is it not a vacume leak that will throw your jetting off blah, blah, blah? I may have to go down to one of my stock vehicles and suck on the hose just to see which way the installed the PCV valve...I swear it is oposite and the check ball has to be overcome by pressure to vent. I hope I'm wrong as now I may be able to jetison the air pump I was gonna use as a vac pump....I toss my valve cover breather every time I rev passed 5k.
 

·
Buick Hybrid Guy.
Joined
·
255 Posts
All OEM vehicles there is vaccume to that line at all times and if you have it started and pull the pcv off the valve cover and put your finger under it it'll suck it to it prity hard :)
With out a vaccume pump or pcv you'll have alot of crank case pressure.. oil leaks ect... Once again... on a street vehicle.. .
~Scott
 

·
Certified Lead Foot
Joined
·
518 Posts
Even though there is no or little measureable vacuum at WOT, there will still be air drawn thru the PCV valve. The engine is pulling max air into the cylinders. Why would an opening into the carb/manifold suddenly NOT flow air.

The amount of combustion pressure excaping into the crank case depends on how well the rings seal.
 

·
Registered
Joined
·
229 Posts
UR50SLO said:
That way, there is air being pulled through the vaccume line opening the PCV valve and pulling fresh air into the crankcase all the time except for WOT.
So am I wrong and it is generally agreed that a pcv valve is installed directionaly so that it can be pulled open by vacume rather than pushed open from crank case pressure overcoming the ball/spring? That's where I'm stuck....and if so, why have a valve at all? Why not leave it open right to the carb since it will be pulling air through the engine all the time.....? Someone is now going to tell me under certain conditions it could flow the oposite direction but without supercharging when would that happen?
 

·
Buick Hybrid Guy.
Joined
·
255 Posts
Someone is now going to tell me under certain conditions it could flow the oposite direction but without supercharging when would that happen?
With out boost... never.. .unless there's a back fire or somthing. The PCV valve does limit how much vaccume is pulled on most of them you can kinda hear it rattling or bouncing the spring and plunger inside. A wide open vaccume leak with 3/8 hose would be alot. I think they use it to limit how much air go's through the passage.
That's my take on the design.. anyone else have another view of why?
~Scott
 

·
Registered
Joined
·
276 Posts
Breather

Question:
If your engine is drawing air from the outside into one valve cover and out the other valve cover into your intake system is it a good idea to install one of those small air filters\breathers on the side where the air is drawn in? I have always done this but I see most engines don't filter this incoming air. What do you think is it important to filter this incoming air?

Bob
 

·
Buick Hybrid Guy.
Joined
·
255 Posts
Yes... exactly how it is.
In the old days when they used carbs they had that little filter there inside the air cleaner that filtered the incoming air.. now days the inlet pipe/hose to the crank case is in the inlet pipe going to the throttle body (after the air cleaner)
~Scottt
 

·
Buick Hybrid Guy.
Joined
·
255 Posts
The incoming air is usually drawn from INSIDE the air cleaner housing, so it's already filtered. Injected cars usually pull the air between the filter and inlet into the engine, again, already filtered.

The older chevies had the little filter because it was on the OUTSIDE of the air filter, but still inside the aircleaner housing...dirty air!
Boy are we on the same page or what :thumbup:
~scott
 

·
Registered
Joined
·
276 Posts
Breather

I guess I shouldn't ask stupid questions. I asked because 6 out of 10 cars at the drags and at local car shows have a breather with nothing but a metal screen filtering incoming air. It seems one of the first things to go on a hot rod here is the stock air cleaner. I realize the aftermarket air cleaners have accommodations to reinstall filtered air but few are installed. My intent was not to disrupt the thread. [ ]

Bob
 
1 - 20 of 26 Posts
Top