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post #1 of 3 (permalink) Old 01-18-05, 07:15 PM Thread Starter
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Recirculation Breather

Hey guys with the tube ontop of the rocker cover to the right (EB i6) a friend of mine told me to piss it off as it recirculated some unburnt petrol/air mixure into the throttle body and put on a mini pod filter, but he is not sure on how illegal/legal it is, and also tells me it will let the engine have cleaner cooler air inturn......any information provided will be highly appreciated


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post #2 of 3 (permalink) Old 01-19-05, 04:59 AM
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Re: Recirculation Breather

I assume you are talking about the PCV (Positive Crankcase Ventilation) system. If so, it's removal is both very illegal and a really stupid idea. The PCV removes blow by gases from the crankcase (partially unburnt gases that get by the rings..and there is always some). If these are left in the crankcase they will cause accelerated engine wear as a)they are on there own very accidic and b) when they mix with the oil they will also significantly reduce the oils lubricating properties.

They are not just an ADR anti pollution thing. Pre 1960"s cars used to use a draft tube to vent them to the atmosphere; this was a downward facing tube that pointed at the road and used the flow of air past the mouth of the tube to suck these gas out (with air coming inthrough a rocker cover bretaher cap). Unfortunately these old systems were not very effective at normal suburban road speeds (and they were also a major contributor to pollution). Using the engine vacuum as modern system do to suck the air back through the air systems is much more effective.

If you have a tired engine with excess blowby you can build an oil seperator into this system so the partially used fuel air mix is recirculated but any heavier oily redidues are collected.

Regards Blue
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post #3 of 3 (permalink) Old 01-19-05, 03:24 PM
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Re: Recirculation Breather

The other thing here is that the idle mixture volume set for the engine, in other words the idle mixture, includes a calibrated amount of bleed air drawn into the engine via the PCV valve. This air is initially drawn from the air claener side of the throttle body, passing into the back of the rocker cover via a rubbber hose. It is then drawn by engine suction (via the PCV valve) across the rocker gear chamber, collecting engine fumes to be burnt along the way. The PCV valve regulates the amount of bleed by a combination of a orifice and the tension of the plunger spring. On overrun, it shuts fully to ensure max. vacuum for brake servo assistance.

To see the PCV's effect on idling particularly, remove it from the grommet while the engine is running. The idle may change a bit, especially if your engine is a bit old and fumey. If you then put your thumb over the opening on the valve (that should be sucking) and stop the air bleed, the engine idle will certainly change, as you have dramatically upset the idle air/fuel ratio. So the best advice is to leave it as it is - working.
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