The Honda spark arrestor hasn't changed much since the early 80's. The "arrestor" is the fine mesh screen that you can see in Dirt699's second picture. The exhaust flows thru the screen, thru "windows" cut in the tube, then out the end. The version of Honda spark arrestor I am most familiar with is the Honda XR400R. The earliest model...like my '96 had a tube similar to the CRF, with very large windows (much bigger than the CRF). Then to quiet it more, there was a "pea shooter" stuffed into the tube after the "windows". Later models had smaller windows, and more restrictive "pea shooters" to meet stricter (lower dB) sound ratings. The size of the windows, the restriction of the mesh size, and the peashooter restriction can make the exhaust louder or quieter, and power is inversely proportional to restriction. The point I am getting to is, theoretically, redesigning the spark arrestor insert with bigger windows, and increasing the inside diameter of the tube may be a cheaper alternative to a whole new muffler to improve power. I redesigned the spark arrestor and peashooter on my XR400, and the power increase was very impressive, and inexpensive. Of course, there are other reasons to eliminate the ENTIRE CRF muffler because it is HEAVY, and there is the additional restriction of the catalyst buried in the muffler. Folks who cut a window in the Yamaha WR250R muffler to remove the catalyst report very significant increase in power. Finally, Rocky Mt ATV sells their Lexx slip on mufflers for many models, and is comparatively inexpensive ($199). It is a very popular exhaust for the cost conscious KLR650 owners. Unfortunately, there is nothing for the CRF...yet. So, bottom line is there may be alternatives to spending nearly $1K on an obnoxiously loud CRF aftermarket muffler.