Chevy 250 - Breather or Cap

[Mthumphrey]

OK guys. I currently have a stock 250 until I get the headers and intake installed. It has one of those air cleaner looking breathers on the stock valve cover and a PCV valve on the back side. I am getting a lot of blow back. I found that the PCV valve connector is all cracked and leaky which might explain a little oil leak I have been trying to fix. The question is... Once I fix the PCV valve connector, should I replace the air cleaner breather with a chrome breather or a cap? Cap or no cap is the question?

I searched a bit and have seen engines both ways. It would seem a cap would be best to close of the unit get a better vacuum in the system, but is there a reason a breather should be used in this instance?

Thanks!

[geezer#99]

You need a breather to supply air into the motor, to mix with the fumes and be pulled out with the pcv.
If you use a sealed cap the pcv deadheads and draws nothing. Crankcase pressure builds up and finds a nice gasket to blow out.

[TJ's Chevy]

Like geezer said...your sucking air with the PCV you need something to help out with ventilation. New breather "air cleaner" style breathers are readily available. I got a fancy set for my 292. It REALLY doesn't matter which on you use. I have both styles on my 292's and each ventilates fine. The blow by you may want to look into. My 305 v6 has Alot of blow by. lol Literally I went to shut the engine off and I could see steam going from under the hood! lol! Runs fine though! So I ain't fixing something that's tryin to act broken.

[Mthumphrey]

Thanks guys! I am not a engine expert and that makes sense, but isn't the engine getting air from the air filter? Why do we see so many caps on them? Just trying to learn here... I appreciate the feedback!!!

[geezer#99]

Air from the air filter is for the carb. You need air to mix with the fuel to make the vapor that burns in the combustion cylinder.

People that just use a solid cap likely aren't aware of the problem they're creating.
Maybe they like a 'leaky messy' motor.

[Mthumphrey]

Got it! Thanks! I appreciate the help! I am not down with a leaky motor... Trying to fix that now.

[Lugnutz65]

Originally Posted by Mthumphrey

OK guys. I currently have a stock 250 until I get the headers and intake installed. It has one of those air cleaner looking breathers on the stock valve cover and a PCV valve on the back side. I am getting a lot of blow back. I found that the PCV valve connector is all cracked and leaky which might explain a little oil leak I have been trying to fix. The question is... Once I fix the PCV valve connector, should I replace the air cleaner breather with a chrome breather or a cap? Cap or no cap is the question?

I searched a bit and have seen engines both ways. It would seem a cap would be best to close of the unit get a better vacuum in the system, but is there a reason a breather should be used in this instance?

Thanks!

Here's a pic of the 250 (1971) that's in my 1965 C10. I swapped a 1965 rocker cover for the 1971 cover. The 71 cover had an emissions vent that fed into the carb so the rocker cover may not look like yours. The 250 likes the breather. I will say that my 230ci had a cap instead of a breather, but everyone agrees that the breather is better.

Also notice the PCV hose has a 90 degree bend already molded into it where it connects. These are available from Truck and Car Shop. Works nice and I like the lower profile.

[vince1]

I think the breather may have been originally put on to vent excessive blow by out. Probably the cap came in with better emissions standards whereby they wanted all the blow by to go through the combustion process again.

[geezer#99]

Originally Posted by vince1

I think the breather may have been originally put on to vent excessive blow by out. Probably the cap came in with better emissions standards whereby they wanted all the blow by to go through the combustion process again.

The mid fifties and later motors had breathers to allow air in, even before the pcv was introduced. The old road draft tubes needed air into the motor too work.
Older 235's and the 216's before that had baffle slots in the top of the valve cover to let air in.
And fwiw the tube off the side of some valve covers was so a tube could hook from it to the air cleaner. It wasn't a true emissions thing.
Fresh air in, crap air out.
We'd still be running those old systems if we didn't have the government emissions requirements and if people didn't complain about that smell from their motor.

[vince1]

The more they wear out, the more blow by past the rings and into the crankcase. It has to go somewhere, in the old days out the side tube, so bad in some cases, it looked like an exhaust pipe.

[TJ's Chevy]

My 305 v6 had a cap style breather with a tube to hook a hose onto that went to the air cleaner. All the blow by went right to the combustion chamber.