For the 2001 S60, this is what Volvo says:
-Drew
[This message has been edited by InDy (edited 06-20-2002).]
For the 2002 S60, this is what Volvo says:
Not sure why things have changed a little, but if you want to change to K&N now, that should not be a problem at all, especially since it is something that is not really cost prohibitive (#33-2176 @ $62) IMHO. I have heard from import owners that it gives a little sportier intake noise.

-Drew
[This message has been edited by InDy (edited 06-20-2002).]