About $2.00 worth of dremel cutting wheels is what it took to cut the spark arrestor and the rest of that little pipe out of my stock exhaust canister on my 450R. Loud as hell but it made a huge difference. Throttle response is FAR crisper now and it seems to rev a lot further out.

 

You should hear my stock exhaust, theres nothing left in it. It seems to pull alot harder.