Im gettin ready to purchase a set of slip-ons for the r1. I know alot of people knock out the cat. out of the y-pipe. My question is how much will it affect the sound of the slip ons or does it really matter.

For me the CAT is a major source of heat and a restriction in the exhaust, but my bike had the Arrows on when I bought it so I can't say if it affected the noise.

I can say that I would have replaced the CAT with a Y-Piece if I was doing it myself.

BTW the noise is just amazing.

I knocked out the cat after I put on aftermarket pipes. The sound is better, but it doesn't seem to get louder until the rpms exceed about 4,000. It's worth getting rid of the cat, whether you knock it out or get a Y pipe.

how hard is it to take out.

Not hard at all. Just remove the "Y" pipe and you will see what looks like a honeycomb of aluminum. I put my pipe in a wooden work bench vise and chiped it out with a hammer and screwdriver. (I first drilled out a 1 1/2 " hole through the middle). Just take your time and it comes out quite easily...it's really brittle. I then took a 2" round wire brush on the drill and "honed" it out after I chipped the cat out. That's it.

Its just a big honeycomb web inside your mid pipe. Just take a screw driver to it !! I bought a grave system so I never did take out the old cat but It looks pretty easy to bang out.

if ur not going to get a full system... then get an akra y pipe, or bang out your mesh in the stocker...