Shakey said:
Also, the VFR folks have actually found cases where the BHP DROPS when a K&N is fitted. I don't pretend to understand why though.
According to every honest motorcycle tuner I've talked to... the air boxes on Jap bikes are so perfectly ported and balanced, all a K&N filter will do is damage that balance.
Ivan of Ivan's Performance Products in New York has tried everything to offer some air box improvements to FZ1s and Hyabusas, because it would be very profitable for him... but he has yet to improve on stock. (He did get some improvement with venting a Bandit intake.)
Ivan will you, in that thick Long Island drawl, he can strap an FZ1 to a dyno... run it, then drop in a K&N filter and show a 2 - 3 horsepower drop. Even with corrected jetting, it doesn't come back.
He gets big gains by altering compression with a different head gasket and exhaust - all with the stock air box. He's quite popular with the 'busa crowd, as he can get them 200 rear wheel horsepower with a simple head gasket and exhaust.
