This video was an inspiration for my bike.
http://www.youtube.com/watch?v=ST4jjH4rPGcSupposedly he was getting less than 10 second 1/4 miles but the internet is full of braggarts. There are lots of comments following the video. One thing I noticed was he really cranked up the sprocket ratios.
Here is a great video of a CR500 with the timing verified. 10.5 at 120mph
http://www.youtube.com/watch?v=RJTuQrSbAfwI started this project wanting a 500cc or a 490 air cooled two stroke. I ended up using an IT400 because I got it for $160. I have only had to add steel for the frame and tires ( and a few others odds & sods) The rest of it was hanging around my shop. I still think there is a latent sub 13 seconder waiting to blossom from this pile of vintage dirt bike.
Peace & performance, Dennis