Somehow I stumbled onto some U-tube videos of a guy who hacked up his CRF muffler. Based on what he did, he appears not to have seen what RamZ did to take out the catalyst http://rickramsey.net/CRF250Lcccmods.htm His videos are http://www.youtube.com/watch?v=tXOmGjSlpTw and http://www.youtube.com/watch?v=AWkCGxiYLfc It at least explains the insane flow path thru the CRF muffler which has the built in catalyst. Having seen the cylinder of catalyst from my friends WR250R, and a description by this guy and Ram Z, the CRF catalyst is about twice the length, and based on 36 years of experience dealing with automotive catalyst system, that double length CRF catalyst has somewhere between 2 and 4 times the backpressure that the WR250R has. Based on my friends performance improvement on his non-catalyst WR250R...which was REAL significant, I would expect the CRF to run EXTREMELY well without a catalyst, as long as the EJK is tuned to compensate for the A/F ratio changes....most likely leanness....that would result from such backpressure changes. Also, based on RamZ sound data, the sound level of his bike, with only the catalyst excised, did NOT change (87dB). That surprised me. Personally, I don't advocate removal of the catalyst, but if you are good with a die grinder, and can weld or have access to a good welder, study up on the pictures, do up your muffler, and have a quiet 100% stock appearing muffler, and save many hundreds of dollars. Now that I know the flow diagram of the CRF muffler, I am going to modify the spare spark arrestor I bought to reduce backpressure, while keeping 100% within the letter of the law regarding sparkarrestor functionality.