An intersting article in Jan. DIRT BIKE. They take a CRF450 and with White Bros. help turn the thing into a dirt tracker. Rules state the 40mm Keihin must be restricted to 37mm with a restrictor plate. They researched and spoke with dirt track and stock car guys for tips on restrictor plates and found that the airflow and turbulence factor is critical . They were told that cutting a small groove on intake mainfold side of restrictor can produce a tiny vortex effect to breathe better. The trick is to make the groove the right width and depth. Then they added a custom W Bros. exhaust. The CRF put out 51 HP... 3 more than the unrestricted CRF. The bike was said to "hang with a KTM520 in every way." It placed #5 in its debut race. Anyone with dirttrack experience want to comment? Anyone want to try it out, and report back? Hey... I'll pitch in 5 bucks. If it dont work, fill the groove back in with JB Weld.