just read thelink to the performance page on that products page. I think it explains everything. What the runners do are sort of channel the air, and when you remove them there is more space for more air, so it becomes more beneficial at high rpms.

Runner length (mm) =( (crank angle degrees)*(speed of sound(m/*)))/(.012*RPM)

I started a post on clubgp.com to see if any of them have had any success with this.