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Message: <blockquote data-quote="garrittpwl" data-source="post: 1542564" data-attributes="member: 21560">Thought I'd share a discovery that I've had recently for those that don't really think about it or just don't know. Its obvious now that I've learned it but no one comes out directly and says "hey, make sure of this because of this" so lets get to it.Why is a a catch can important specifically when using running a turbo?If you're unfamiliar with turbo setups, they require oil (well most, some new fancy ones dont). That oil has to be pumped into the turbo via a feed line, then regulated to a pressure that the turbo can handle and then evacuated via a drain line to the oil pan.Turbos lower than the oil pan require a scavenger pump to pull the oil from the turbo to the oil pan. Turbos higher than the oil pan can gravity feed back to the pan provided its a steep, smooth straight line.Now lets get to the point. Since I slapped an on3 kit on my car last summer, I've always had a little smoke at the stop lights here and there. Nothing that a few blips of the throttle couldnt clean up. I equated this to a cheap chinese turbo seal. What I discovered was that in actuality my turbo was not draining efficiently. But wait?! I did everything correct, ran a nice -10 AN line from the turbo with a smooth turn right into the top of the oil pan right?WRONG!!!! I used an amazon catch can with a vent that was only 3/8 in diameter! So my vent system from the crank case had TWO -8AN lines running to the can and then a single 3/8 vent to atmosphere.I found that since the crank had such a small vent. I was creating a positive pressure inside the engine, very small but still positive. That pressure would slow the oil in the turbo's drain just enough that it would enventually (long cruises for example) not allow the turbo to drain properly and oil would seep around the seal on the exhaust turbine side. This in turn caused it to smoke!I watched a video about diesel guys having the same issue, though now it seems common sense. Basically like trying to empty or fill a gas can that doesnt vent properly.Seems silly but I thought I'd put some info out there in case someone in the future was trying to diag their turbo smoking.Below I attached a picture of my newly acquired motion raceworks catch can vs the amazon one I was attempting to use. Now I know why they're 200 bucks instead of 30.....[ATTACH=full]34381[/ATTACH]</blockquote>