When I went to the races sunday, I met a guy that had just bought a z-400 the day before...he wasn't racing it...not broken in yet. But he also has the DRZ-400S. The same engine that's in a Z. He said that he took the end-cap of the DRZ and removed the spark arrestor. He told me that it opened it up a bit and makes it sound like a Yz426. He put the end-cap from the DRZ on his Z-400 and it really does make a difference in the sound. He let me use it in one of the races, but I didn't notice any difference in power. I was wondering if any of you have thoughts or ideas on this.