I want to put an oil catch can on my car for the blow byand I want to get a nice one so not only will it look good but perform good. I was looking at the Greddy that I found here http://www.optionimports.com/oilcatchcan.htmlbut I don't know which size to get 9mm or 15mm. Which one do you think will work best.

 

SHould be 15mm since i think when i did mine i used 1/2" hose. I use a air compressor filter setup you can get at Home Depot/Lowes and all the fittings for $35 and works better than those setups. If you want something like that, just get a ebay look a like and fill it with steel wool and your set.