Here are some runs on the new '06 Yamaha YZ250F. Yamaha made a few changes to the cylinder head for '06, resulting in 1 more hp in box-stock condition. (run 003, not the same bike as the rest of the report but it works for comparitive purposes) A customer had me build his with a Wiseco +2mm overbore kit utilizing their "new" piston, and a little bit of head porting. (run 004) There wasn't time to deal with camshafts, those were installed at a later date. (run 010) Finally, a FMF full exhaust was tested, which really uncorked it. (run 016) The secret to a really fast YZ-F isn't in the individual parts, it's the combination of parts and the tuning.