PCV Nipple placement

[turbosax2]

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Can anyone tell me why Mitsubishi places the PCV nipple where they do on the intake manifold?

I'm installing a vacuum block onto my Evo III intake manifold that is fed from the plenum. This leaves me with the option of plumbing the PCV line to the vacuum block, or leaving it in its current location. The green line above shows the "hump" where the PCV inlet connects to each of the four runners internally, so I'm not sure how moving it the plenum/vacuum block would really be that different. I've been trying to think of pros and cons to each location, but the only one I've been able to come up with is that if I leave it in the stock position, any oil that gets through my catch can will only contaminate the runners in the intake manifold rather than contaminating everything fed by the vacuum block.

Opinions and ideas welcomed!

 

[romeen]

Personally, I would recommend leaving it hooked up to the stock location. I say this because of the way the small ports (connecting PCV "hump" to runner) that are located in the top of each runner (looking in from cylinder head side) are pointed directly at the intake ports of the head. It's like that on the 1G and Cyclone IM's I have here as well. The way that they are deliberately pointed the way they are suggests to me that Mitsubishi has a good reason for the way it is.

This is just speculation but it may have something to do with minimizing turbulence where the two streams of air from main flow path and PCV merge. I wonder if it might also help to regulate the amount of positive pressure directed toward the PCV valve when under boost. Lastly, it might work to more evenly distribute the crankcase gases so that no one cylinder is more contaminated than the others.

Just my opinion.

 

[turbosax2]

Your reasoning sounds sensible. Thanks for the input!

 

[Ceddy]

I think the placement and angle helps create a siphon effect. The fast moving air pulls the pcv gasses in.

The muscle cars guys do something similar with an angled nipple attached to the exhaust. Even though the exhaust is always at positive pressure, the siphon effect causes a vacuum at the nipple.