On my Thruxton, have a krankvent with a 2" X 1 1/2" rubber topped K&N breather that butts up against the bottom of my fuel tank, between the right carb manifold and rear cyl head frame brace. Harley site says krankvents do not make hp; http://www.nightrider.com/biketech/crankvent_test.htm

Cheers..............Agro