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Discussion Starter #1 (Edited)
I know has been discussed various times with filters etc.

My connector got broken so I attempted to hook up a system of my own but I think it was too restrictive.

Since then I have just placed a 0.5 litre bottle (with an open hole on 1 side) that is fed directly from the side oil filler tube. Few drops of oil have filled it up already.

At idle it puffs away nicely, you can feel the air coming out.

Now what happens at fast revs? Is a negative pressure created within the crankcase? or is it still safe just to have the filler open into a bottle - free to the air basically with no restriction.

No emission tests here btw.

Do I need a filter on this to prevent dust from being sucked back in? This is another doubt I have or is it always under positive pressure?

-alfsud 1981 just has a pipe pointed down to the ground - no ill effects at all
 

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I drove 2 years with KN filters on my 33ti. I just let it vent in to free air. No problems what so ever. My Sprint just vent into free air as well. No problems what so ever.
 

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Most if not all modern cars run positive crankcase ventilation, where the crankcase is connected to the intake system. 2 reasons - to collect emissions of oil fumes from the hot crankcase and feed them back into the engine to be burnt, and secondarily to provide a partial vacuum in the crankcase (caused by the vacuum in the intake between throttle/s and cylinders) to reduce windage - the drag on crank and pistons caused by having to move air out of the way as they rotate/move up and down.

So if you don't have this system on a sud/33 carb motor you will get some fuming and eventually some liquid(ish) oil hence why people fit a small catch tank. Of course you should block off the 4 little tubes that go to each intake or your engine will suck in extra air after the carbs and so run lean, mainly at idle and low revs. In theory you will have a small power loss also due to more air resistance in crankcase, but of course at wide open throttle there is virtually no vacuum so it will have no effect at max attack - why many race cars have the system disconnected. Serious race engines use dry sump with scavenging pump to evacuate the air and oil at all revs to reduce windage.
 

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Discussion Starter #4
Great good to know.
Yes the small 4 inlets are blocked off.

It will just breath feely into the air form now on.:)
 
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