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The mkiv Supra Owners Club

Thoughts surrounding crankcase ventilation


SteveR

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At the moment, my breather pipe vents to atmostphere via a little filter like a baby K&N or something (ahh bless).

 

Anyway, I was planning on getting a nipple welded onto the air intake, between the air intake filter and the turbo - then the crankcase would see negative pressure almost all the time the engine was running and all the nastyness within it would be sucked into the turbo and burned up in the engine - winner.

 

Or so I thought. A friend of mine (Sevenman on here - and an avid SAAB fan) emailed me his thoughts;

Have been pondering the location of the Saab’s crankcase ventilation and reading up on the topic.

 

Saab vents right to the inlet manifold, after the throttle body.

 

This is an area which :

1) Has positive pressure under boost

 

2) Has negative pressure on overrun and gentle driving.

 

Fumes will be drawn in during case 2) and burnt

 

During case 1) the valve stops the crankcase from being over-pressured.

 

 

Historically the valve has been there to stop the crankcase vapour igniting if the engine backfires, but in a turbo car it serves 2 purposes, and a failed valve is bad.

 

Also historically, the crankcase vapous have been vented to atmosphere using pipe under the car. This was stopped in the 60s when it was found that this account for 50% of the car’s hydrocarbon emissions, and was also leaving an oily film on the road…

 

Piping it to the area between your air filter and turbo may be bad. This could coat turbo, intercooler, and all pipes inbetween with oily stuff. I believe quite a lot of stuff can come through that way and it may not be ideal.

That is why I think the saab has gone for the option of introducing it right before it goes into the cylinders.

 

I would research what lots of other cars do before you plumb it in that way…

 

http://en.wikipedia.org/wiki/PCV_valve

 

Reading that link and considering the options, I'm inclined to have a rethink, but I'm no expert so I'll take advice form the floor...

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If you run a catch tank in between, then only vapour goes into the intake and not oil mist, whats being refereed to in that piece is just the PCV that the Supra has on the intake side anyway, i removed this and vent both sides to a catch tank and then into the intake before the turbo, it doesn't produce any oil.

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