OutLaw305

I was wondering


WHy do some cars run dual breathers and some have one breather and one tube coming off the other valve cover?
What are the reasons for either?



EDIT: did a search and see that it is for crankcase ventilation. I still dont understand why or whynot to use duals or single breathers though.


duals:

OutLaw305

tube:

OutLaw305

If it helps, I am going to run a carbed 350, not my stock tbi 305.



these are my valve covers.

"Manufactured to GM specs, these premium valve covers are equipped with internal oil drippers and OEM-style baffles."

Air_Adam

Thats a PCV valve.

People with two breather caps (one in each valve cover) don't have a PCV system. Thats not necessarily such a bad thing, as cars worked fine for many years without them, but IMO, you should use a PCV valve on any street engine. An engine with two breather caps is just vented, so its still very easy for crud to build up inside the engine, and the breather caps can make a hideous mess of your engine on the outside.

I say use PCV because it will keep the inside of your engine and the oil cleaner, and it will also keep the outside of your engine cleaner too, espeically around the breather cap, because it sucks up all the fumes inside the engine and puts them into the intake to be burned.
The way I have mine set up is a PCV valve in the pass side valve cover, and a breather cap in the driver side valve cover. The hose on the PCV valve (on mine anyway) was just hooked up to a vacuum port on the intake manifold.

Air_Adam

Heres a pic of the pass side... you can kinda make out the PCV valve between the 2 back plug wires:

Air_Adam

Heres the drivers side, with the breather cap:

Matt87GTA

Run a PCV system. Your engine oil and thus the engine itself will thank you by living longer.

OutLaw305

On my engine now, i have the one tube ( i belive this is the pcv tube) that goes from my drivers side valve cover into my manifold. On the passenger side i have the tube pictured below. This is the one i would swtich over to a breather correct?

OutLaw305

i should prob put the pic in..



(yea its dirty, its also an old pic. Just using it as refrence.)

Matt87GTA

Yes, that is the one that brings filtered fresh air into the crankcase either via that foam element in the air cleaner assembly or from behind the filter element in the air intake stream or through a breather element (filtered as well). It is important that this intake of air to the crankcase be filtered so the fresh air is clean. Keep in mind that baffles are often necessary to keep oil from splashing up into the filter element and being forced out under high RPM conditions where the crankcase needs to vent out through the breather. This will make the big mess of oil spattering around under the hood that people refer to when running breathers that are open element ones. A good baffling setup will stop this on most engines. If you have excessive blow-by it will tend to generate so much crankcase pressure even under normal operation that the PCV system will not operate properly and the breathers will become soaked in oil and make a mess even with good baffling.

I have always run an open element on one side and a PCV valve on the other side on my engines. Either that or leave the factory system in place.

Air_Adam

Yes, the tube in your pass side valve cover is the one you replace with a breather cap. All that tube does it act like a breather, but it pull in air from your factory air cleaner.