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MG MGA - Engine ventilation with a Judson

I am just about to pull off my twin SU set up and replace with the Judson supercharger. For the former I had a breather hose connection from the cover to one of the filters. The Judson cover has a breather valve fitted . I believe a hose connection to the new single filter would be a better arrangement than the breather valve to allow more forced ventilation . All advice welcomed......
Neil Ferguson

Neil, note that the air flow should be from filter (clean air) to rocker cover, not the other way round. The draft tube under the car should be the crank case gas exhaust (the angle at the end will draw air out on forward motion).

Not sure how effective this is when stationary, but in any case I suspect is not in line with a forced ventilation.
N McGurk

Neil, I always thought that the "breather" on the rocker cover is just that, a breather out, and not an intake? I often get oil dripping into the front carb filter from condensed oil fumes coming through from the breather, and this is why I have some fine mesh under the rocker cover to reduce this.
Gary Lock

Air normally goes from air filter to valve cover, through the crankcase, and out the draft tuba when the car is moving. When stationary the crankcase fumes can escape both directions, which can occasionally leave a bit of oil in the air filter.

Valve covers are supposed to have a metal shield below the breather port to prevent direct splash of oil from rocker arms getting up the pipe, but vapor fumes can certainly carry a little mist when escaping in that direction.
Barney Gaylord

Two comments..
..the pressure inside the filter housing is slightly vacuum ( approx 1in wc) so I would consider that the fumes would preferentially move upwards through the cover or ,at least the flow must be hindered in the opposite direction.
...The recommendations on this site generally have been to hook a hose between the cover and the filter .

Why should the recommendation be different for a Judson equipped engine ?
Neil Ferguson


Your comments are slightly confusing.
Are you measuring the vacuum inside the filter itself?
Is the car stationary?
Is the engine running?
It is difficult to understand how you would be getting vacuum anywhere in the cover if the car is stationary. This is normally when you get some positive pressure in the crankcase with the engine running.
If the car is moving you would expect a slight vacuum at the filter but the air movement would be downwards through the valve cover.

M F Anderson

Venturi action of the draft tube is very effective pulling air at road speed,producing substantially more vacuum than you find inside the air filter element (which isn't much).
Barney Gaylord

Mick...Engine is running..whether the car is stationary or moving is not relevant . It is the engine speed and therefore the engine pump effect that creates the air flow and hence the small press loss through the filter into the container. If there is a hose connecting the filter housing to the cover then air will flow to filter until car moves and the pull due to forward speed referenced by Barney below becomes greater than the filter effect.

Barney..Thanks for comment and on that basis I see no need to tube up the Judson cover to the filter ..just have the correct breather valve...which is the one that came with the restored unit fron George Folchi.
I also recollect seeing a valve that can be mounted on the crankcase to vent via a hose to ...???
Neil Ferguson

Original Judson supercharger kit did not include any kind of valve. What kind of "valve" did George supply with the supercharger? Some sort of a PCV valve, maybe? How about a picture of the valve, and where it mounts?
Barney Gaylord

Barney....possibly my last post was confusing. George supplied a cap that fits into the cover. You can see the same on the pics on your site of Judson installations. I don't think there is much is just a vented oil filler cap.
The second sentence refers to a special crankcase ventilation valve I had seen somewhere ...turns out it is on your site and was used on mgb's and it is hooked up to the intake manifold by a hose..this was not fitted on cars of our vintage .
Neil Ferguson

Okay, got it. The tall cylindrical oil filler cap has ventilation holes around the bottom skirt, and horsehair or steel wool filter inside. It serves same purpose as hose from valve cover to air filter housing, to filter air going into the crankcase, so no hose is required. Under the circumstances when this breaths out rather than in, it can leave a few drops of oil on top of the valve cover rather than in the air cleaner. It only depends on where you prefer to deposit the little dribble.

The PCV valve shown on my web page is from MGB, late 1964 thru 1969 models. It is to be plumbed from front tappet cover to the intake manifold, and in conjunction with sealed crankcase with filtered and restricted air inlet (usually at the valve cover). Air inlet changed a couple of times, detailed here:
Barney Gaylord

Dribble is a terrible a few years it might refer to my mouth and chin...
Neil Ferguson

Barney...just read your CV102 and I am about to install the Judson over the coming weeks with a non standard inlet manifold made to accommodate a SU HIF 44 with a K&N conical filter ( instead of the Holley). I note your comment that from 1970 onwards the MGB used the SU venturi tapping to get ventilation sucked through the crankcase whenever the engine was running and it should help reduce/eliminate the 'drip' we all love . I am keen to do this as it seems reliable with no additional moving parts to be necessary ..just a hose. What size hose is needed and do I just plumb up the draft tube to the venturi connection with hose clips .
Neil Ferguson

The pipe on the front tappet cover is always 1/2-inch. With normal dual carbs there is a "T" fitting with 1/2 inch inlet, and the two outlet branches are smaller, maybe 3/8 inch going to the carbs. With a single carb you may have to settle for a 1/2 to 3/8 reducer and single 3/8 hose for the final connection at the carb.
Barney Gaylord

This thread was discussed between 17/03/2012 and 20/03/2012

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