Quit letting these fools feed you lines of bullshit. Anyone worth their knowledge will know that muffler bearings are bullshit as well. The way to go is spiral flow muffler gaskets. They stick into the airstream just slightly and create a spiral vortex effect with the exhaust gasses. Spiraling air moves through a pipe much faster than air being pushed in a "lump" so to speak. For the best flow on those yoshis you need two of them, one on each side. A bonus is that they will increase peak torque, the V-twin guys love them. Plus since you are removing so much backpressure from the engine it's going to go lean. I'd suggest a "green" filter. They really are green. Put one in and you'll cancel out the loss of backpressure and flow way more air which will bring you back to a slightly rich condition. This is good. The spiral flows can be had from Indysuperbikes.com or DucRX on here. You gotta call both places and ask. They are kind of an "illegal" off-road only part so they aren't readily advertised. As for the green filter, you can find that anywhere. Quit listening to these wannabe yahoos and listen to the engineers. I've been in and out of these inline 4s for years and I know what I'm talking about at least.