TMU

I have a PCV valve to the carb on one side and a breather tube to the air cleaner on the other side. Is there any reason to keep the breather tube to the air cleaner instead of just using a mini breather right at the valve cover? Will it not vent enough of the fumes?

toobroketoretire

The G.M. engineers designed it that way to prevent dirt from getting into the crank case as well as preventing the acid-laden fumes from contaminating the air we breathe. The same reason the "road draft" tube at the rear of the block was eliminated back in the early '60's.

TMU

Thanks. I need new grommets and though to maybe just replace the tube system and go with a filter.

JC68

TMU

It doesn't really matter where you get the clean air from on a PCV system.

If you get it from the air cleaner it is called a "closed" PCV system, if it is gotten from a breather on the valve cover it is called an "open".

In the late 60's Chevrolet used both types on their cars. For most engines the open system was standard. Option K24 would let you add the closed system. The closed system was required on all cars delivered in California.

I believe all Corvettes that used a PCV system received the closed type as standard.

John

Big2Bird

It will work. Just remember under hard WOT, the PCV does nothing, and the high crankcase pressure can make the fumes come out the breather.
A closed system vents these back to the air filter where they are burned. An open system, the oil vapor goes in the engine compartment.

TMU

Sounds like a grommet hunt is a better idea.

Thanks!

TMU

I've got an after market air cleaner, but the base has the hole for the breather tube and it looks like someone used a 73 breather tube setup on my '68.

Thanks!

vetteus

I prefer the aftermarket push in breathers only because the original setup with the small diamond shaped filter tends to fall out of the holder attached to the air cleaner. I also think the aftermarket ones breath better.

stumpshot

I've used variations on both a 350 and the present 383. I like the connection to the air cleaner and the pcv to the carb combo on my '75.
Reason? I don't like the smell that blows out of the intake filter on the valve cover on let-off.
Try any combo you like----it's your car and you will get no performance increase out of any combo. If you don't like one, try another. Grommets and filters are cheap and you need a spare box of "Once tried" parts anyhow!
Stumpshot

cardo0

PCV is a flow regulating vlv controlled by vac in one direction and a check vlv in the other. The higher the vac press or the higher the crankcase press (from blowby) the higher the restriction to flow. As the throttle opens and vacuum goes down the spring inside the PCV moves to open the vlv more (moves the restriction plug to allow more flow). Same thing for increased crankcase press. But when vac increases the little plug moves to a position with greater restriction and reduces flow. This prevents creating a large vacuum leak at idle and closed throttle. Same thing when crankcase press reduces. And if the the motor backfires the little plug inside the PCV seats in the opposite direction and prevents reverse flow - like a check vlv.

Moving the filtered air from the air cleaner to a filter on the vlv cover changes nothing, absolutely nothing. But u will want to plug the hole in the A/C if source moved to the vlv cover. The key component is the PCV and that is sized for your engine.

Franks73

Maybe it's just my imagination, but I think the fumes were noticeably reduced when I went back to the stock GM design of routing PCV through the air filter assembly.

'75

Less smell and mess when a closed system like factory is used. Excess fumes that the pcv doesn't handle are ingested and re-burnt. Most of the aftermarket air cleaners will have an area to be cut out for the vent tube from the valve cover to be attached.