I hate to say it, but if you can already beat 400's, there's something wrong with them. (either rider, or quad) Not saying that it can't happen, but with no more mods than you have, the 400's have to be sick, or the riders can't ride, OR your not telling us the whole story. With all of our mods on our Blaster, it would keep up with my stock 400, but I could still out run him. Just not by much, and thats with my son only weighing 80 lbs. Now that I cam'd my 400 with the pipe and rejetted, its no race.
As far as mods go, If your going to port it, do that first then buy a carb and reeds to feed it. Probably have to get a new air box to fit the carb.

 

i have only beat those machines on the track. i would not be able to beat those machines a a drag. unless they were bone stock. if its long enough drag once i topped out thats were they would pass me.

 

i know u said u dont want a bore but if you r thinkin of getting one get a 240 but amke sure you got a really good carb and port job or it ownt make as big an effect, with a good carb and port job the 240 kits make the blaster littl speedy monsters and if you get a small swingarm extension liek 3 or 4 inches it will keep the front end down