Cappuccino in autocross grid

Project Cappuccino: Installing an AOS

Catch cans and air/oil separators are needed for any performance car, but especially turbocharged cars.  We were seeing so much oil in our intercooler piping we thought our turbocharger seals were failing!  Mike already has a great video on how they work and why you need one, so let’s just skip to which AOS we chose for our Project Cappuccino, and how we installed it in the car. 

Suzuki Cappuccino engine bay emphasizing the PCV system layout and the factory AOS
The Cappuccino already has an AOS as part of its PCV system. Unfortunately, it is not a well designed AOS and lets a lot of oil into the intake tract. The big tower on the left side of the cam cover is the factory AOS. Blow by is vented through both valve covers into the box. This is then vented back into the intake just before the turbo.
Screenshot of the Cappuccino service manual showing and describing the PCV system
This snip from the Cappuccino FSM shows how the box captures blow by gasses and vents them into the intake tract. AOS systems work by slowing the speed of the air to the point that the oil droplets literally fall out the vapor. A well designed AOS will slow the airspeed, gather the slowed oil, and return it to the oil pan. I had the privilege of working on Eaton’s aerospace AOS systems that could not only remove the oil, but also any metallic debris picked up from an aircraft engine, turbine, or gearbox. They used basic physics applied in a clever way to do all of this.
Interior of the Cappuccino's AOS box
Suzuki did not. The PCV feeds from the big port on the right and exits through the small port on the left. There is no baffling or any divider to slow the air/oil mist. Mist enters the box and gets sucked right into the intake (which is under vacuum). Our original plan was to try and add baffles to the tower to slow the oil and get it to drop out. However modifying this part without over pressurizing the crankcase or creating leaks was a bit too risky.
Cappuccino AOS gasket and crankcase vent
It doesn’t help that there is additional upward venting coming from the valve cover itself. Basically all of the vented air in the PCV system is forced upwards towards the intake vent and nothing slows or redirects it so the oil can separate and drop back into the head. This system is cumbersome and most racing Cappuccinos remove the AOS and just vent the system into a catch can. Fun fact, if you install this particular gasket backwards, it screws up the PCV system so much oil will literally blow out your exhaust. Ask me how I know!
TakeOff headlight mounted catch can
The quick solution is to buy this kit from TakeOff that adds a basic catch can to the PCV system. It replaces the 5” long 90° hose with a custom made can that sits behind the driver’s side headlight. It’s 100% bolt in and can be installed in a matter of minutes at a very reasonable price. However I didn’t go this route. First, this is just a catch can and not an AOS. Notice how the intake and vent ports are side by side. There is no baffling or divider in the catch can so it’s going to have the same problem as the stock AOS. This can will also capture condensation and be unable to vent it, making a nasty oil and water slurry. This can also has to be completely removed from the car to drain it and adds a bunch of unnecessary weight and clutter to the engine bay. I wanted something simpler, more compact, and better suited to higher boost and performance driving.
J&L Air Oil Separator Packaging
We picked J&L’s universal Air Oil Separator 3.0 for the Cappuccino. The primary reason is that it is very compact. Engine bay space is at a premium in the Cappuccino so finding a small can is necessary. J&L makes bolt-in AOS kits for dozens of vehicles but adapting their universal AOS for the Cappuccino is pretty easy. The universal kit includes a couple of premade brackets and some assorted fittings to plumb it. Final mounting and sourcing of the hoses will need to be done by the owner.  All J&L kits are made in the USA too which is a nice touch.
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1 comment

  1. Hi Dave,
    Fellow Cap owner here, enjoying your articles! Thank you.
    A clarification please, in your latest article about installing an AOS, you mention a gasket in the factory AOS which, if installed backwards, blows oil out of the exhaust.
    In your photo above this mention, is that gasket the correct way around (small square hole to the front), in your opinion?
    I ask because in the Cap service manual and Megazip parts diagrams, the gasket is drawn with the square hole to the rear (although the diagrams aren’t very clear!). When I checked my own car, the hole in the gasket was towards the rear, as per the diagrams.
    Best regards
    William McDougall

    Reply

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