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A lot of people run Oil Catch Cans on the PCV circuit, but very few run them on the Valve Cover Breather circuit as well. It seems like the main reasoning for this is that there isn't nearly as much oil blowby present in the Valve Cover Breather circuit.

I'm wondering if (in addition to a catch can on the PCV circuit) it would be beneficial to install a catch can into the Valve Cover Breather circuit as well.

I'm thinking that it may not only help with reducing blowby vapors into the engine, but also help with the smoking @ idle that is so prevalent.

I've read through these threads:

http://forum.mazda6club.com/mazdaspeed6/228611-mazda-admits-smoking-problem-11.html
How to install PT performance Oil Burning Fix - Mazdaspeed Forums
Official 'Smoking Turbo' response from Mazda - Page 24 - Mazda Forums

The threads talk about a fix for smoking @ idle that a lot of people seem to notice especially after a DP or TP install.

Here is the fix that is discussed - PT-Performance.com

This fix is based on the idea that the smoking issue is fixed by reducing air flow that is going into the crankcase via the valve cover breather and therefore increasing the amount of vacuum created by the PCV system. Apparently, during low loads the vacuum is needed to allow oil to drain back from the turbo into the pan instead of slipping past the turbo seals.

This fix seems to work for a lot of people. Also, people who have installed this are reporting lower Knock Retard numbers, which makes sense because during WOT the flow is reversed (when PCV is closed) and air is flowing from the crankcase through the valve cover breather into the intake, along with oil vapor. So the reduction in flow is resulting in less oil vapor and lower KR numbers.

I'm wondering if adding a catch can to the valve cover breather circuit would accomplish the same thing; adding restriction to the valve cover breather hose to increase the vacuum in the crank case while the PCV system is active and thereby fixing the idle smoke issues just as the PT-Performance restrictor pill does; Also, it should do even more in regards to reducing Knock Retard since not only is the flow being reduced, but oil vapor should be further reduced because of the catch can.

Thoughts?
 

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It HAS been done. But, I couldn't possibly comment on the results.
Personally, if I had the cash lying around, I would do it myself. I know there's plenty of vapor introduced here, just from visiting my intake tract from time to time...
 

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Another thing that helps with smoking at idle, is bumping your idle up to 950. We were rolling around today, and had some very noticable vibs at idle because of the mounts w/ the A/C on... it doesn't really bother me, but I know some people raise their idle to reduce the vibs. So, I just raised the idle on my maps to 950 and I'll see if that helps with smoke. It probably won't be sufficient alone to stop the smoking, but I may try that restrictor pill or bolt thing when I get around to reading up and them and seeing what I think. In the meantime, I'll see how the higher idle works by itself.
 
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