[T3] cylinder head breather ports on a 1972 Squareback

[Jim Adney]

On 5 Aug 2013 at 22:49, Dave Pallo wrote:

> [[[Without fresh air getting into the case, there will be a bit of a vacuum
> in his case, much of which will be alleviated by blowby and vapor from any
> gas in the oil. This should not cause any problems.]]]
>  
> My '72 with its PCV system intact draws what I would call a "fair" amount of
> air from the crankcase. If I were to plug the ports on the heads - the
> vacuum draw would pull air in from somewhere. I know blowby would make a
> contribution by adding air into the case, but I think there would still be a
> need for more air into the crankcase than that (especially on a new motor),
> and I would bet the easiest place for the crankcase to draw in air would be
> around the crankshaft behind the fan, where there is no seal, and this would
> be unfiltered air being drawn into the crankcase. When VW used the heads
> with breather ports made just for a PCV equipped motor - these are not small
> ports ( about .5" diameter X 2), and they made sure the air entering these
> ports was filtered air by running hoses up to the air cleaner. In my
> opinion, if anyone was running an intact pcv equipped system - they should
> have a way to allow filtered air into the crankcase, just as they did at the
> factory. Jacob mentioned valve covers with breather ports in them. I've
> never seen them myself, but if they have a way to allow air in - and filter
> it - I would consider using them since he doesn't have the heads with the
> ports. Just my 2 cents...

I agree that the best solution is the complete system. Not letting 
any air in the heads is only 2nd best.

Keep in mind that the air drawn in is no more than is drawn out via 
the vacuum in the IAD. That might seem like a lot. (It's max at 
idle.) But there's a pretty small orifice in that tube leading into 
the IAD. The amount of air that can get in there is pretty limited; 
it's not nearly as large as the hose leading to it might make you 
suspect.

Also, the passage for air to get into the case at the rear is pretty 
small, and mostly blocked by oil from the #4 main bearing.

And, yes, any air getting in at the rear would be unfiltered air. 
Certainly not the best solution.

-- 
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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