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Catch Can with or without PCV? Which is best?
Side-Oilers:
My Kirkham 427, with a fresh aluminum 482 engine, is getting a bit of blow-by on the passenger side during deceleration, from approx 3000 rpm and up. The engine is great other than that.
I installed an M/E Wagner adjustable PCV, connected to passenger side valve cover, and to a vacuum port under the carb. I tuned it for the optimum vacuum, etc.
The other valve cover has a period-style Ford breather.
I'm now thinking I need a catch can. So, is it better to run a closed system that retains the PCV, or an open system with no PCV, and vent(s) on the catch can?
I've read that the vented can scenario is the race car type (not really necessary on my street driven Kirkham) and will emit a fuel or oil vapor when the car is idling, like at a traffic light.
I'd appreciate anyone's thoughts, opinions, best plumbing ideas, recommended hose sizes, and anything else. 8)
s2ms:
I'm using a Bob's Machine oil separator on my 66. Otherwise stock PCV valve and closed breather setup. Works great and fits with no modifications, the bracket is attached to one of the export brace bolts. Probably overkill at this point as I finally was able to fabricate a baffle that is working well, originals were removed to fit roller rockers/polylocks, but it still does catch some oil so keeping it installed for now. I used repop PCV hoses and cut to fit.
shelbydoug:
--- Quote from: Side-Oilers on April 20, 2021, 10:36:48 PM ---My Kirkham 427, with a fresh aluminum 482 engine, is getting a bit of blow-by on the passenger side during deceleration, from approx 3000 rpm and up. The engine is great other than that.
I installed an M/E Wagner adjustable PCV, connected to passenger side valve cover, and to a vacuum port under the carb. I tuned it for the optimum vacuum, etc.
The other valve cover has a period-style Ford breather.
I'm now thinking I need a catch can. So, is it better to run a closed system that retains the PCV, or an open system with no PCV, and vent(s) on the catch can?
I've read that the vented can scenario is the race car type (not really necessary on my street driven Kirkham) and will emit a fuel or oil vapor when the car is idling, like at a traffic light.
I'd appreciate anyone's thoughts, opinions, best plumbing ideas, recommended hose sizes, and anything else. 8)
--- End quote ---
I am running this setup and it's my opinion (sometimes I even argue with myself though) that it is more of a skimmer then anything and is only going to have a percentage of effectiveness.
I find very little oil in my "catch can", mostly an inch or two of water.
So really, it's anyones guess how well it really works?
Maybe look for a catch can from a current tight emissions car and see if there is internal switching on them.
Thinking about it, I think there is an electrical connection to the one on my Audi and I need to investigate why.
They are most likely on the car to protect the cat from further contamination from oil deposits?
Good question but I don't know the answer to your question. Just speculation since I'm only as far along as you are.
shelbydoug:
I found that the best setting on the Wagner is using the under 10 inch method. It completely shuts off the valve at idle and results in higher idle vacuum.
I went from 12 inches to 16-17 inches at idle on the same 236@.050 cam. That's all in the pcv system. I'm very happy about that.
That was basically just changing the spring in the Wagner valve.
I don't think that you need an open breather in the valve cover. The air cleaner is essentially functioning that way already. Take off the top of the aircleaner while the engine is idling. Look at the water vapor coming out of the connection. That thing is open already.
Try closing up the open valve cover. See what the results of that are? If you really want to be scientific, you could hook up a vacuum gauge somehow to the pcv system. You don't want more then about 12inches otherwise you'll suck in things like the crank seals which I would predict to be a bad thing.
The header scavaging system provides something like only 6 inches but most racers use it these days, but talk about sucking oil out of the covers and making a mess? That's it.
The suction point is too low and will encourage siphoning oil out of the valve covers.
pbf777:
--- Quote from: Side-Oilers on April 20, 2021, 10:36:48 PM ---.................... a bit of blow-by on the passenger side during deceleration, from approx 3000 rpm and up.
--- End quote ---
I gather with your concerns of valve cover attachments that your reference of "blow-by" is as observed from the valve cover breather? Not from the tail pipe? :-\
--- Quote ---
I installed an M/E Wagner adjustable PCV, .................................... I tuned it for the optimum vacuum, etc.
--- End quote ---
"Optimum vacuum"? A control setting for the implied "ideal" operation? Really! And how is this "ideal" actually going to be established "in-the-field" and with which parameters for observed function or result? ???
Now I'm aware of perhaps (depends on the application) an observed loss in the vacuum value (change in manifold pressure) within the induction system when a P.C.V. valve is instituted, and a at times real concern for this effect (particularly on a carburetor) but?
In my opinion this is a perfect example of creating an implied need, then with a product (gadget) to solve no real issue, but in the price range that will lead to many a "what-if' or "why-not" sale! But it is a cool billet gizmo anyway! ::)
Scott.
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