a 3.25" tube will provide more than enough air for this engine.So I just cut my 90 degree elbow that was in the fender off so it's a straight shot into the intake. The pipe that goes into the fender is only 3.25" or 83mm so it's definitely still too small, I ordered a 101mm maf adaptor for my air filter to attach to in the fender. With the 3.25" pipe on it, I am now pegging my lightning maf...