I'm no expert on this so someone please correct me if i'm wrong. There are two breather lines coming from the valve cover, one goes to the intake manifold (through the PCV vlave) and the other goes to your air intake pipe. An oil catch can can be installed in series with either or both of these lines. Its purpose is to extract the oil and other waste products from the blow by gasses and prevent them from being recirculated back into your engine. If the oil in the blow by gasses is not removed it will lower the octane rating of your fuel and line the insides of your intake piping and intercooler with oil and muck. I'm not sure about the installation as i have never attempted it before.
There is a few on ebay for about $65. Not sure if there is much difference between an ebay OCC and a brand name one.
You will still need the PCV valve as this stops boost pressure from the manifold entering the crank case.
The attached PDF is a bit long but has a lot of info.
Hope this helped
Last edited by Toddy22587; 28-02-2010 at 01:30 AM.
To fit an occ in the correct location, i.e from the PCV on the block, under the intake manifold is a pretty big task.
I had a crawl around under there some time ago, and it pretty much involves working blind with your hands contorted to some amazing angles, it can be done, and has been extensively documented on some of the US forums, some have even suggested that removing the entire intake manifold, although more time consuming, makes the job a lot easier.