yeah 2" piping - with 2" turbo outlet, any bigger on that side is silly IMO, and 2" on the throttle body side fits through the stock hole and joins to the stock piping where the stock BOV bolts onto (although my BOV is blocked off anyway, you get the idea though).
i'm just having major dramas with the car though.........i'm 95% sure i have no leaks (i can pressurise the intake, block it, and release minutes later and the air rushes out - holes pressure fine), it cold starts + idles fine, cruises fine, but idle when hot is hunting terribly (think almost stalling to 1500rpm or so, back and forth on its own), and it sounds like it's making boost but makes very little and goes nowhere. i gotta go over and double check all the sensors and stuff, especially AFM, maybe i stuffed the plug from unplugging it so many times. will throw consult on it tomorrow.
anyway the new intercooler is so much better looking than the old trashy one, the piping is heaps shorter and with less bends too. i'd like to redo the piping from turbo->i/c at some point, but it'll do for now. the mounts i made are pretty hardcore - can hold the i/c and shake the car around it's so sturdy!