Are there any reasons you wouldn't install an oil catch can on a carburettor'd 3.5?

Oldskoolrob

Active Member
Hi gurus,
One of my rocker covers vents into the base of my air filter (holley carb), the other has a breather on it. This is how the mechanic set the car up for it's roadworthy cerificate. Yesterday I found a small amount of clean engine oil under the filter element. I may have overfilled the oil last time I checked it so I'm not hugely concerned (but I am a little bit) but it got me to thinking I should install a catch can. Is there a 'best' way to do it? Should I install a separator instead? The car doesn't get driven often and is usually a cruiser with the occasional 'spiritied' jaunt.
Cheers,
Rob.
 
Did your mechanic fit a PCV valve between the carb base and the rocker cover?
 
No he didn't, but the original set up I had with the SU's didn't have one so I didn't think to put one in. I may have an old PCV valve lurking (I used to be deep into Holdens which had them). Does have a flame trap. I think the catch can/separator might still be a good idea, I don't like the idea of feeding the engine oil....
 
Are all the breathers free , I know there was another one on the back of the V8 on the early Range Rover & if blocked would pressurise the engine and blow oil out of the rocker cover breathers.
 
There is a small one on the back which the mechanic (a Rover specialist) has crimped to block it. Should I open it up, and if so to ambient or air-filter vacuum? On the holdens I used to play with we'd always have a breather on one rocker cover and vacuum on the other, to create a single path,
 
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Riiiight. So to confirm (remembering this is a Holley/downdraft set up and the carby has no vacuum port at the base)- one rocker to atmosphere, one and the rear vent to air filter vacuum?
 
You could fit pipes and flame traps to both rocker covers, then "T" those together and run them to inside the filter housing, on the engine side of the air filter element. Then open up the pipe at the rear of the engine, fit a hose, then a fuel filter, then another hose to run to the filter housing but this time on the outside of the filter element. That will be as close as you can get to the OE setup.
 
If you wanted to get closer still to the OE setup you could fit a carb spacer with a vac port, similar to this:

M153711163.jpg
 
Thanks Harvey, as always I appreciate your advice. That spacer is interesting - I was considering a small phenolic one...
 
You might need a spacer under the Holley to get a PCV system working.
This is a 1" alloy one from an Autolite 4100.
IMG_2480.JPG
I used a Phenolic one, and tapped in a vac stub in the rear. The vacuum is ducted underneath to come from the primaries only.
I had to do a lot of work to make it right, for a start it was warped and I had to sand it flat on a sheet of glass, then fit the stub and create passages to the primaries.
I did all that as I could not find an Autolite one, then of course managed to locate one, which is why I have the above one as a desk ornament :rolleyes:
 
Izzat for laughing gas?
Oldskoolrob, what intake manifold is your Holley attached to? The Offenhauser is a bit lower than the Edelbrock Performer. I once had the latter with a 390 on it and there wasn't a lot of room left under the bonnet, with only a thin phenolic spacer in place, and a low profile air cleaner on top. I had to trim down the stud for the air filter, a lot! Just a thought. Measure what space you have available before hitting that 'Buy it NOW!' button.
What bad things are happening inside my engine without an upside down plastic fuel filter on a bit of hose attached to the stubby pipe on the back of the OS cylinder head? I just have an open pipe there at the moment. Any comments, wise elders?
 
What bad things are happening inside my engine without an upside down plastic fuel filter on a bit of hose attached to the stubby pipe on the back of the OS cylinder head? I just have an open pipe there at the moment. Any comments, wise elders?

As long as the hose/pipe isn't blocked then it's not a problem.
 
As far as I can remember, and it's been a while, the original emission control on a P6B is fairly basic. Air goes into the air box, then is fed down into a tube in the rear of the engine via a short hose and filter (crimped off in Oldskoolrob's car). This air then goes down into the crankcase and winds its way up to the rocker covers, picking up fumes, oil mist etc as it goes. It then goes through the breather pipes, flame traps and into the carb (I believe) behind the butterflies. When the butterflies open, these fumes get sucked into the combustion chambers and are burnt.

The filter on the back is to stop dusty dirty air from entering the crankcase. You don't want any grit in there :)

The four barrel carbs have a PCV port which is open to full engine vacuum. You do need a PCV valve which allows low flow under high vacuum (i.e. tickover/overrun), and opens up for higher flow under low vacuum (WOT).
 
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