Testing Radium Engineering's Advanced Self-Draining Catch Can!

by Mike Kojima

Having proper crankcase ventilation is critical on a performance engine, especially forced induction ones that have more blowby past the rings by nature. The pressure needs to be relieved. Excessive crankcase pressure can blow seals, cause severe smoking from the turbo and affect piston ring seal causing smoking and losing power. 

Good crankcase venting is more than just having an open vent line to the atmosphere or back into the intake. In the vent gasses, oil vapor from crankcase windage and drain back from the top end of the engine is expelled with the blowby gasses. Sometimes the amount of oil expelled can be considerable, especially with forced induction with track driving where you are at wide open throttle.  

Because of this most race sanctioning bodies and track day organizers require that catch cans be used on all breathers.  Another issue is that sometimes so much oil is expelled to the catch can that it can have a negative impact on sump levels during the course of a race. Low oil pressure and blown engines have resulted from this.

Boxter engines like the ones found in Subarus are particularly susceptible to poor crankcase venting issues, especially boosted boxers. This is because they do not have the benefit of gravity to help return oil and heavy oil laden vapor to the pan. Our own Project STI had some issues with turbine seal smoking because of excessive crankcase pressure and due to the high volume of oil expelled from the breathers, we felt that a self-draining crankcase return catch can was a must for our car. 


Radium Engineering had a self-draining catch can solution we felt was a great choice for our STI which sees track duty and also serves as a daily driver. The Radium can is a quality part, black anodized and made of drawn tubing and CNC-machined end caps for reasonable weight and good solid threaded areas for the hose fittings. 

The Radium catch can not only self-drains but has some really cool features that make it great for daily use, particularly in short haul driving with frequent stops and for use in cold climates. 


The Radium catch can comes with a Subaru specific bracket in our case but it can be had with universal brackets as well. The can has some nice quality banjo fittings for the vent lines and an atmospheric filter for the vent gasses although it can also be routed back into the intake to make a sealed closed loop system for emission friendly use. 

The cool stuff is what is inside. In the can which can be disassembled in case you want to thoroughly clean it out, is this green extruded heating element. Coolant from the throttle body or some other source is routed through here. When an engine is started, it expels quite a bit of water vapor from the blowby gasses, as water is a combustion byproduct. The vapor is like a heavy stream for the first few minutes of operation until the engine is completely warmed up. 


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Dan DeRosia
Dan DeRosialink
Friday, April 07, 2017 6:57 AM
Argh, more things to buy for the WRX. I'm continually annoyed at all the ways Subaru got things *almost* right, but I'm not really sure what I'd replace it with.
Friday, April 07, 2017 8:54 AM
Man.... tight fit with the aftermarket strut tower brace but it clears!
Friday, April 07, 2017 10:44 AM
If you have that much crankcase pressure a leak down test would be a good idea.

I like catch cans/ air oil separators, especially on Subarus, but it would be nice of someone to actually do some data-logging/dyno testing. I would expect keeping oil out of the intake tract should reduce IATs, knock, and increase power marginally but I haven't seen anyone actually do it. So there are a ton of forums guys going on an on about how they're dumb and useless. I suppose that is up to radium, crawford, iag, etc to do though.

Side note, we had a pooly baffled AOS on the time attack car back in the day and it turned out to be dumping a ton of oil back into the intake. After venting to a separate catch can we no longer were losing oil through the breather system and made 40 more hp next time on the dyno.
Mike Kojima
Mike Kojimalink
Friday, April 07, 2017 1:37 PM
That is interesting.
Friday, April 07, 2017 7:14 PM
Boxer mike, not boxter heh
Name User
Name Userlink
Friday, April 07, 2017 8:20 PM
wassup goony jamal, 5 years ago I asked you where to take my Evo to in LA. now 400whp later I'm losing 1/2 a quart of oil every 200 miles on a stroker

Compression is fine, but I would be filling up these Radium cans every week, I wish they made the jumbo one for the Evo 8/9 mounting kit

other than the insane blowby it's actually fine, even the blackstone lab results. I think the 9mpg city driving affects my situation too
Friday, April 07, 2017 10:39 PM
Hey Name User, I assume I said RRE, they are good guys. Speaking of evos and time attack, we had issues with the pcv system on a high powered one and had big fittings and a big can and it still pushed a lot of oil out. We even had to zip-tie the dipstick down because the blowby would pop it out, and this was a cosworth 2.2 long block.

I would have to guess your problem is still excessive blowby, and that probably means a ring sealing issue. But talk to the road race guys, they know evos way better than I do.
Mike Kojima
Mike Kojimalink
Saturday, April 08, 2017 1:13 AM
This can has a drain to the crankcase so it won't be filling up. Evo's have really poor crankcase venting so the can blow a lot out of what breathing they have.
Name User
Name Userlink
Saturday, April 08, 2017 4:41 AM
Jamal, yup, thanks for getting me started, didn't know where to begin back then. And yes the dipstick ziptie budget is part of the weekly oil level check ritual.

Thanks Mike, I'll contact Radium about mounting options, this is probably the way to go for me. Don't want to rebuild yet
Mike Kojima
Mike Kojimalink
Saturday, April 08, 2017 9:09 AM
I would mod the valvecover and have a dash 10 coming out of it.
Monday, April 10, 2017 9:05 AM
As a BWM E46 owner in cold weather I have been tempted to buy a catch can. I like that this one is self draining and heated, as one problem with the E46's CCV is that the oily goo freezes in the winter and plugs the CCV, leading to some potentially catastrophic results.
After a few CCV replacements and an oil pan heater, I've settled on opening my oil filler cap every day when I get home to let the oily goo evaporate. This seems to work pretty well but it's a pain.
I wonder if this catch can would be even better with an electrically heated element to cook off the goo?
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