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breather can or catch can?
Posted by: Unsafe140 ()
Date: March 01, 2022 08:47PM

This has been covered in other posts of the past to some degree.
It seems like there is not really a consensus on which way is the best
with corvair crank case pressure.

Lets assume for argument that one of these two is going to be put into service so we dont need to discuss ring problems etc etc.

Many of us could learn from the set ups and experiences out there...

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Re: breather can or catch can?
Posted by: vairmech ()
Date: March 02, 2022 04:17AM

I made my own! I didn't like the small size of the ones offered nor the really huge ones offered.

I plumbed mine so it will self drain. I did a post a while back explaining the construction.



Ken Hand
Handy Car Care
248 613 8586

Vairmech@aol.com

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Re: breather can or catch can?
Posted by: Phil Dally ()
Date: March 02, 2022 06:09AM

I use three Jegs one quart breathers with -12 fittings.

From both valve covers and the former fuel pump boss.

We figured more is better at 7K+ rpm and 148.253 mph.

Fuel pump boss is almost perfect for 3/4"-16 pipe thread.

The breathers are mounted in the former battery location.


Attachments:


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Re: breather can or catch can?
Posted by: Unsafe140 ()
Date: March 02, 2022 07:07AM

Yes Phil I think you may need the extra volume in your case!
So we have one for catch can and one for breather.
Ken I did see that pic in the other post when i was searching nice work.
Did you road draft the top tube?

I would like to decrease crankcase pressure especially when in low or no
vacuum situations. That leads me to a breather type set up, yes? Although there is
the argument for creating a large vacuum leak if its set up to return to intake and air cleaner. Is this a valid argument?

Or maybe the extra overall volume created by a catch can is enough to reduce cc pressure? Then we can still run a closed system.

Love getting in the weeds on this stuff.

Thoughts

And thanks for the pics always helpful!

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Re: breather can or catch can?
Posted by: Phil Dally ()
Date: March 02, 2022 07:15AM

I do drain oil from the breathers occasionally so they also work as catch cans.

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Re: breather can or catch can?
Posted by: Timothy Shortle ()
Date: March 02, 2022 07:49AM

Seems like back in the olden days of cheap Corvairs some had some type of homemade contraptions
but it always seemed to be related to worn out engines and cheap owners. Ken and Phil are all
about high stress engines in their race cars.

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Re: breather can or catch can?
Posted by: 66vairman ()
Date: March 02, 2022 08:29AM

Unsafe140 Wrote:
-------------------------------------------------------
> Yes Phil I think you may need the extra volume in your case!
> So we have one for catch can and one for breather.
> Ken I did see that pic in the other post when i was searching nice work.
> Did you road draft the top tube?
>
> I would like to decrease crankcase pressure especially when in low or no
> vacuum situations. That leads me to a breather type set up, yes? Although there is
> the argument for creating a large vacuum leak if its set up to return to intake and air cleaner. Is this a valid argument?
>
> Or maybe the extra overall volume created by a catch can is enough to reduce cc pressure? Then we can still run a closed system.
>
> Love getting in the weeds on this stuff.
>
> Thoughts
>
> And thanks for the pics always helpful!

When racing, or with an engine that has worn out piston rings, the crankcase ventilation system can be overwhelmed with oil vapor. Outside of those conditions the Corvair Positive Crankcase Ventilation (PCV) system works well. It's a PASSIVE system. No magic. It's set up so the crankcase AND inlet to the manifold vacuum balance pipe, via a PCV valve or fixed orifice, IS ALWAYS AT ATMOSPHERIC PRESSURE. This is done by facilitating consumption of crankcase vapors via the manifold vacuum balance tube, or at greater throttle openings excess vapors go into the carburetor air cleaner and are ingested down the carburetor(s). If the crankcase doesn't produce enough gasses then air is drawn from the air cleaner so a vacuum is NOT created in the crankcase. Think of the tube to the air cleaner as a two way path to keep the crankcase (and input to the PCV valve or fixed orifice) at atmospheric pressure.

An elegantly simple design that works well and doesn't cause vacuum variations at idle that would upset the air fuel ratio.

NOTE: This system was developed by GM during WWII so military vehicles could run partially submerged in water without letting water into the engine crankcase. There was a lot of research done to make sure it wasn't detrimental to the engines operation. After the war it was first used on luxury cars to reduce the "stink" from the engine compartment into the passenger compartment via the windows in summer or heater in winter.

During the start of the emissions era it was found the PCV system reduced engine emissions considerable without any detrimental effects on engine performance. What about oil vapor ingestion? Does anyone recall when folks put "Marvel Mystery Oil" systems on cars to let them ingest the oil to prolong valve and ring life?

BTW - all this information is online.

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Re: breather can or catch can?
Posted by: vairmech ()
Date: March 02, 2022 05:22PM

Unsafe140 Wrote:
-------------------------------------------------------
Snip-
> Ken I did see that pic in the other post when i was searching nice work.
> Did you road draft the top tube?
>
> I would like to decrease crankcase pressure especially when in low or no
> vacuum situations. That leads me to a breather type set up, yes? Although there is
> the argument for creating a large vacuum leak if its set up to return to intake and air cleaner. Is this a valid argument?
>
> Or maybe the extra overall volume created by a catch can is enough to reduce cc pressure? Then we can still run a closed system.
>
> Love getting in the weeds on this stuff.
>
> Thoughts
>
> And thanks for the pics always helpful!
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

The top is open vent of course. But with what I have posted the down and dirty way on the race car is a catch can. What was used? How about a windshield washer plastic container with just a hose into it!
If you really look at my picture there still is the vacuum PCV tube.

Ken Hand
Handy Car Care
248 613 8586

Vairmech@aol.com

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Re: breather can or catch can?
Posted by: v8vair ()
Date: March 02, 2022 06:31PM

With a good tight ring seal and a proper baffle in the oil pan and top cover you shouldn’t see any oil in a catch can ,I do get a little mist out of the added drivers side vent in the top cover. The only thing I’ve gotten out of my breather tank is water !!! Go figure smiling smiley

1964 Bill Thomas Monza Replica Racer
1964 Spyder Street Car
1998 Honda Prelude Dirt track car
1967 Crown V8 under construction
Mike Levine

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Re: breather can or catch can?
Posted by: Phil Dally ()
Date: March 03, 2022 05:25AM

Yes, what drains out is more like water with oily residue.

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Re: breather can or catch can?
Posted by: Unsafe140 ()
Date: March 03, 2022 08:24PM

Thanks for the responses. I went ahead and bought a breather can that i can choose to use the top filter vent or not.
If you are pulling out oily water from the system that should mean better
oil and decreased friction, no?
I imagine a cleaner intake as well thumbs up

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