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PCV Catch-Can Part 1: The Problem

The Problem:
In trying to track down a mysterious loss of power, I'm now focussing on a serious oil sweat coming from the turbo compressor housing. The compressor housing is covered with baked-on oil, which seems to be dripping down from the joint between itself and the #2 air pipe (pipe that carries air from turbo to intercooler (IC)).

This oil could be coming from a worn-out turbo main bearing, but I don't think so. There's no oil in the exhaust, and the boost gauge says my turbo is healthy. I think the oil is coming from the PCV line, which feeds into the intake just a few inches ahead of the turbo.

I found this very interesting reference on the web:

Re: MR2 Turbo PCV catch can legal in SCCA Stock class?

From "Burns, James B."
Date Tue, 13 Oct 1998 08:34:44 -0400
Cc MR2-Interest List

Ricardo Martinez wrote:
Looking at the SCCA Solo2 Stock rules, it looks like pcv catch cans are legal provided that the pcv system is not altered. I've interpreted this to mean that I can run some kind of oil catch can as long as there is no "breather" out to atmosphere associated with it. Is this true? I'd like to clean all the oil residue out of the intake, but I don't want it to build up again if I can avoid it.

I interpret the rule the same way you do. You can put a catch can in middle of the PCV line as long as the line then continues to the stock location on the intake pipe. I have also considered doing this mod since on the track I sometimes get oil sucked through this line into the turbo during hard right hand corners. Oil builds up at the top of the head at high RPMs and during hard right handers it sloshes to the left side and goes into the PCV line. When MR2 Turbos used to race in IMSA they were required to make a PCV mod due to this problem, but I don't know exactly what this mod consisted of.

Have you found a good place to mount the catch can?

Brad Burns

Well that clinches it. "High RPMs" and "hard corners" describes 90% of the driving I do. I need a PCV Catch-Can.

Background: The PCV Circuit, and Catch-Cans
Pistons and piston rings do note make a perfect seal with the cylinder walls of the engine. Some air/fuel mixture and some combustion gases blow by the rings and enter the crankcase. These blow-by gases would build up and cause problems if they were not vented in some way. This is the job of the PCV (Positive Crankcase Valve). The PCV lets these gases out through the valve cover, and recirculates them back into the engine intake, to give them a second chance at being properly burned and disposed of through the exhaust system. Unfortunately it seems that some oil bubbles through the PCV line and gunks up the intake tract, including the turbo (compressor side), intercooler, throttle body, and all the piping in between.

I could just disconnect the PCV line from the intake, but that creates its own problems. First, it would not be emissions-legal. The crankcase gases contain a lot of gasoline and oil vapours, which would be a significant source of "hydrocarbon emissions" if not properly recycled. Second, even without considering the liquid oil in the line, the oil vapour would condense all over the inside of my engine bay and make a slimy mess. Third, some engines depend on the slight pull of the intake on the PCV line to keep the crankcase properly cleared of vapours.

A catch-can is a can that you introduce in the line between the PCV and the intake, to separate the oil from the vapours. The vapours are either vented to atmosphere through a filter on the top of the can, or continue through the line to the intake as before. The filter approach is used on racecars because they don't have to meet emissions laws, but in a road car it falls victim to the three problems mentioned above. I'll be making up an in-line catch-can which maintains emissions legality.

Part 2: Making and Installing the Catch-Can