vetteguy75

Got these today from Edlebrock and noticed the driver's side has the set up for a PCV and the passenger side valve cover doesn't have a breather hole, but it does have a screw-in oil cap instead (the picture looks like both valve covers have breather holes, but one cover has a threaded hole).

Is this set up "bad" for the engine? Will it affect the engine's performance? Does it have the proper ventilation? I feel a company such as Edlebrock who makes quality products, wouldn't design these covers without the proper engineering...it other words...doing it right.

With this in mind, I called Edlebrock and expressed my concern about the "ventilation" and their tech dept told me that I needed to purchase this breather/PCV combo from Mr. Gasket and that would solve the problem.


...so I did....never heard of such a thing, but I figured they should know what they're talking about. Then I started to read past threads on the forum about having a PCV and no breather and got a range of answers...from "that set up will work" to "you need to have a breather".

Shouldn't there be only 1 answer? If the engine needs a PCV & breather, then why didn't Edlebrock design the valve covers accordingly and have a breather hole and not a screw on oil cap???? Or does it really matter????

SH-60B

I think some of the older motors had a breather that was not in the valve cover. Some had the oil filler in the front center of the block. Those valve covers could also be a "pre PCV" valve design. An old design was a hose exiting a valve cover and routed straight down to end in the "airstream" underneath the car. That was supposed to create a vacuum and draw vapors out of the crankcase.
Our engines do need a PCV and a breather. Just a PCV alone will lower pressure in the crankcase (and keep seals from blowing out) but it wont evacuate the blowby gasses from the crankcase. You need to get blowby gasses out because they contain the contaminates we are trying to keep out of the oil, like water vapor and unburnt gasoline. A vent in the other valve cover allows the PCV to draw clean air through the motor. At high enough engine loads (with enough accompanying blowby) the PCV "system" can get overwhelmed and you can get discharge from the breather. If the breather is in the air cleaner it won't spit crud on your motor, it'll do it in the air cleaner. Those are beautiful valve covers. I hope you can get the PCV set up with them.

BarryK

actually, the pre-'68 small-block motors had a vent hole in the back of the block (not a hose from the valve covers) that went into the aircleaner housing for air intake into the block and than used a vented cap on the oil fill tube to release the vapors and pressure. This usually made a messy engine compartment as the vapors, containing oil mist covered everything in the engine bay. Eventually, in '66, they went to a PCV valve plugged into the oil fill tube with a rubber hose to the carb and the oil fill tube had a sealed cap. The rear vent was used for intake and the PCV valve was the exhaust side of the system.

The newer generation of blocks starting in '68 did not have the rear vent hole machined in the block and the PCV system was designed differently via the valve covers. The PCV valve was put in the drivers side valve cover and connected to the carb via a rubber hose and the breather vent tube went on the passenger side valve cover and went to the air cleaner housing.

BarryK

Vetteguy75
you definitely want the PCV valve in your drivers side valve cover and a seperate breather in the passenger side valve cover. Having a unit that acts as both PCV valve and breather, both on the same valve cover is not as effective.

The PCV system is designed to allow air to travel thru the crankcase, pull the unwanted vapors out, and direct them to the carb to be burnt in the combustion chamber. With a stock set-up with the breather (with filter) or vent tube going to the air cleaner housing on the passenger side valve cover it sucks the fresh air into the block (via vacuum coming from the other side). That fresh air travels thru the crankcase pushing out the vapors thru the drivers side PVC valve and into the carb. It's the connection here at the carb that not only exhausts the vapors but also is where the vacuum comes from to draw the air in on the breather side of the system.

By having this combo breather/PCV valve unit on one valve cover only it's not allowing the fresh air to travel thru the crankcase to get the vapors out. Mostly all you are doing is relieving pressure and exhausting some vapors but it's not as effective as a correct system.

FB007

Just because it fits, does not mean it is correct for your application.

Fevre

You can buy screw in breathers

http://store.summitracing.com/egnsea...alse&N=700+115

SH-60B

Um...OK. So much for history. Vetteguy, I think we all agree you should have a source of clean air with the PCV valve to evacuate the crankcase.

...Roger...

Thats the ticket a filler cap and breather in ONE.

minxdog

is a tube to the breather/air filter really necessary or will something like this work?

http://www.jegs.com/i/Edelbrock/350/4405/10002/-1

BarryK

nothing to do with preference, it's the way it was designed to be done from GM because it's more effective that way.
The oil that's thrown off the crank and rods goes DOWN on the driver's side (away from the bottom of the oil drainback holes), but on the passenger side that oil is thrown UP (toward the bottom of the oil drainback holes). Putting the valve on the driver's side reduces the amount of oil "pullover" (liquid oil) the valve has to deal with (vs. just the hot oil vapors it's designed to meter).

Durango_Boy

That'll work just fine. All you want to do is have an open port on the passenger side, and filtering the incoming air. That's all it does. Now, if you don't have a separate oil fill cap, you must pull the breather out every time you want to add oil.

noonie

That is not correct.

The purpose of the pass side breather is two fold.

Under normal driving conditions, when blowby is low to medium, the breather sucks in filtered air to mix with the blowby gases inside the engine. This is when the pcv valve can handle all the glowby gases by itself.

Under high rpm, there is an increased amount of blowby gases, and a reduced amount of vacuum, and the pass side breather reverses and becomes a crankgase vent the same as a pcv. The excessive gases, that the pcv valve cannot handle completely at this stage, are expelled thru the pass side tube, into the air cleaner assembly and thru both filters and down the carb throat.
That is why on high mileage engines, you may find oil in the bottom of the air cleaner assembly. If you just put a vented cap there, you will end up with a dirty valve cover.

Auto makers have spent big bucks to design this system and everything has room for improvement, but in rare instances has a shadetree been able to improve on it for daily driving. In fact there are problems with the pcv system in the new Z06's, despite GM's high powered engineers.

BarryK

[QUOTE=jerrylee;1566690884]dumb engine builder..... he should have known better.
Anyway, again, look at the reason GM designed it the way they did and make that decision yourself....... but if it was MY motor I'd switch it so the system works as efficiently as possible.

Durango_Boy

That makes a lot of sense, I stand corrected. Thanks.