Learn me oil catch cans

Thinking about installing an oil catch can on the Mazdaspeed3. The car is stock aside from an intake. The goal is primarily to avoid carbon buildup on the back of the valves, direct injection and all that. 

It seems pretty fool proof to me with a caveat.

One of the vendors on a different forum posted their findings comparing different configurations. The one I would like to do has the crankcase at ambient pressure to slightly positive pressure under most conditions. Under full boost the pressure is comparable to other configurations. The stock configuration has the crankcase under slight vacuum but runs straight into the intake manifold through a PCV valve. The configuration I’m looking to do pulls everything through the intake (pre turbo) eliminating the need for the PCV valve. That’s appealing to me since the valves have a reputation for leaking. 

Anyway, is having the crankcase at ambient pressure as opposed to slight vacuum going to be an issue? Keeping oil off of the valves is really appealing but I can’t shake off the idea that Mazda made the system they way they did for a reason and I shouldn’t go messing with it. 

Am I over thinking this?

You're not overthinking it, there are a lot of different configurations to consider.

Connecting the system to the pre-turbo intake means that any traces of oil that do make it through the catch can will get oil into your compressor, charge piping and intercooler.

The slight positive pressure does have some downsides, like faster oil soiling and engine seal wear. Ideally you want the crankcase to be under a vacuum for oil cleanliness and seal life.

I think the best setup for you would be to put the catch can between where your engine and PCV valve are on the stock setup. This will reduce the amount of oil ingested, maintain current crankcase pressures, and keep any traces of oil from getting into the compressor/IC/charge piping.

good thread with a lot of the same questions i've been pondering lately with my ms6.  catch can is probably going to be one of the next things i do to it, i just don't know which one i'll go with. at the moment i'm fairly sure i've narrowed it down between corksports & JBR's. We'll see

Recirculating oil back into a forced-induction engine effectively lowers the fuel's octane level, which is almost always a bad thing.

I assume we're talking about the CS OCC.

I installed the older JBR Stage II with a check valve rather than the open air one because there were some problems with the CS ones blowing up at the time. That said, the design has been redone by CS and appears to be functioning properly now.

I'm pretty sure the slight vacuum in stock configuration is done for emissions reasons but that's more a question for AlfaDriver.

I put one on my SHO last year, a JLT.  It essentially replaces the PCV valve.  This is what was in it after about 8k miles of driving: 

After it settled for an hour or so:

It seems to be mostly water with some other combustion leftovers mixed in.  I honestly don't know if it helps or not, but it can't hurt, I figure.

Thanks for the input guys. 

Basically I am comparing the JBR method to the CS method. I plan on building my own can and hooking it up in the best configuration. 

To anyone not familiar, the Mazdaspeed has two lines. One from the valve cover the intake, preturbo. The second goes from the crankcase to the intake manifold. 

Gameboy: If I install the can on the crankcase line, which seems to be where most get installed, should I consider one for valvecover like too? Last time I had the intake system apart I didn’t notice any oil residue or puddling and I was looking for it. 

Ideally, I would only install one can for cost/space/simplicity reasons. Maybe it’s back to the drawing board. 

I want my gaskets to be stopping air from getting into my oily spaces, not stopping pressurized oily stuff from getting out onto my garage floor. I also want to help stuff that might be in my oil but that could gas out to leave the oil and go somewhere else. I have also studied thermodynamics and the idea of raising the pressure on the non-working side of the pistons and introducing more air into the space where non-aerodynamic spinny wobbly bits are moving around makes me a little queezy.

Put me solidly in the crankcase at a vacuum camp.

I have also had to clean oil out of the inside of an intercooler before and can assure you that under no circumstances do you want to vent that stuff somewhere so it has to go through the cooler.

spandak said:

Thanks for the input guys. 

Basically I am comparing the JBR method to the CS method. I plan on building my own can and hooking it up in the best configuration. 

To anyone not familiar, the Mazdaspeed has two lines. One from the valve cover the intake, preturbo. The second goes from the crankcase to the intake manifold. 

Gameboy: If I install the can on the crankcase line, which seems to be where most get installed, should I consider one for valvecover like too? Last time I had the intake system apart I didn’t notice any oil residue or puddling and I was looking for it. 

Ideally, I would only install one can for cost/space/simplicity reasons. Maybe it’s back to the drawing board. 

On the 2.3L DISI platform the valve cover line is typically only routed to a secondary VTA can in big boost situations. My catch can is only installed on the crankcase line and I haven't had any nastiness in there with the exception of that time I blew up the turbo and blew a liter of oil into pretty much everything.

I made this up back when I was racing my SRT-4.  There were always debates on routing.