The Stovebolt Site Forums The Shop Area Engine Shop 261 pcv system

I have a chevy 261 six... The pcv valve is off the road draft tube and has number ac 1544935... Upon disassembly it looks like it is more of a specific sized orifice as you can get flow in both direction and it doesnt look like there are any moving parts inside.. Is this a true pcv valve system?

In relation it had a rochester carb 7015013 which is specific to chevy 261

Is carb designed/jetted to be used with this specific pcv valve (control vacuum leak)

This came off a running motor so everything worked in present configuration.. Im asking question as ive swapped out a zenith 270 gmc carb (runs great) but am just adding pcv system ... Compatible with zenith carb?

An non-valved connection would go to the air cleaner. Not to a vacuum source. If it is connected to the carb, or the intake you will get a vacuum leak. You will not be able to tune for that.

This is a factory setup for chevy 261..was in 2 ton grain truck.. Ran in present configuration with present pcv valve.. I ordered another pcv valve (same part number) and it is identical with small orifice and nothing else.

At idle with high vacuum you would have a given flow through orifice just like normal pcv valve.. As throttle is opened and vacuum drops.. The flow would also drop... No vacuum leak as.. No vacuum. Sound correct? Seems like a workable system considering grain trucks were full throttle most of time

Doesnt matter too much .. My original question of whether it would work with a zenith carb off gmc 270... After thinking about it it shouldnt matter.. Im putting system in this weekend so ill post results later

I have the same set-up,(Factory),on my T.F.'55 261. My draft tube/P.C.V. valve, is plumbed into the base of the intake manifold. I did have a crankcase pressure issue with this present configuration,though. Since then,I installed a vented oil breather cap,plumbed for a P.C.V.valve. This is now routed to the air breather. The engine's been running fine,since the up-grade,and it does not leak/burn a drop of oil. As far as your carb. swap is concerned,I'd think that your fuel/air adjustment,(with a vacuum gauge),will help you achieve peak performance. The 270's (that I've seen),have similar P.C.V. set-ups.

To give an example of the lack of a PCV valve on a modern engine, I had a 1990 Jeep with a 4.0 L engine which only had a tiny, hard plastic vacuum line coming from the valve cover. The diameter of this pipe served as the metering function similar to what a PCV valve would do. Once again, an example of "there's nothing new" in the world of automobiles.
Carl

My 261 came from a fuel delivery truck circa 1959 and rebuilt stock.

The PCV is the spring plunger type (also used on Mil. Jeeps and CCKW)and runs from the draft tube to the vacuum side of the intake just below the carb. The draft tube has no other openings. The valve cover only had a sealed screw on cap at the front for oil filling and the back nearest the carburator had a 1/2 tube/rubber line attached to the clean side of the air filter of the engine allowing make up air.

My 261 valve cover will be replaced by a 216 military cover with its own mini oil bath air filter in an attempt to disguise the engine.

Cheers
Bob C