I was scrolling through this link... http://www.mototuneusa.com/the_need_for_speed.htm The author has an interesting take on porting...it seems to follow the Power/James/AvNow concept where less is more with regard to flow. He is essentially narrowing the flow passages rather than the conventional enlarging/polishing that is commonly performed. He makes quite a case for it. If you look to the bottom of this link, it is articles 16 and 17. 16 explains the theory and 17 shows you how to begin. I have not tried this at home, but thought it might make for interesting experimentation. He did not perform this on a dirt bike, but it looks like the theory could crossover. If you cannot get in, then try going to mototuneusa.com and register to receive the newsletter.