Nuhaus, I hope Tomtom will respond with his thoughts. I've tried these mods on smaller bikes and really they make little difference except for the sound. A motorcycle engine is in many ways like an air pump there's not much point in having a fast exit for exhaust gases if the way in is as slow as ever, I've tried just putting on a straight-thru muffler, but I think it was a mistake. I've tried removing the air-box and putting on a clip-on fliter which helps the bike suck air in but really if the EFI or carb do not allow a better fuel mix you'll just end up making the bike more lean, sometimes if you have a cheapo Chinese carb bike you can fairly easily raise the needle height or put in a bigger jet and then get a tad more horses maybe half a one, but I don't know if I'd bother trying to second guess Italian or Japanese EFI tech design without a dyno. Obviously with some racing bikes they have open-mouthed after market mufflers, however these are generally tailored to each bike specifically and have been tested usually giving extra power at the sacrifice of some torque. IMHO, and I'm no expert but those baffles, spacers and the cat is in the muffler because it is a street bike to give you back-pressure to keep the torque which makes the bike more usable for a real world non-racing situation and obviously more environmentally friendly too. I for one wouldn't want an inline 600 on the road that was sluggish in the mid range torque band but was marginally more powerful around the red-line.