[SlowToady]

Not really sure, except to say that it was done (an option?) on 993s. From what I understand it doesn't increase HP so much as just makes it sound "meaner."

IIRC, these engines don't have much trouble breathing, and a K&N would be basically a waste of money. There is also a lot of debate about whether or not they are dangerous for engines.

I'd suggest reading a lot about them before putting one in.