Cannot remember where I got them but some foam filters that fix to inside of airbox gave me 4 bhp more than bell mouth 'bathsponge' and kept the intake growl too!!
I have he JHP filters that fit on the airtubes as they enter the airbox. These are said (!) to be much more effectuive than the sponge over the bell mouth filters. They are also very free flowing. They resemble a conical gauze K&N type filter. Induction roar good and none of the 998R's ponies seem hesitant.............
Sounds very similar but mine are made of foam, definitely better than the 'bath sponge' arrangement, but still cannot remember where I bought them.....doh!!!