Hello,
I'm in the middle of a slight recommission of my recently acquired 906. I noticed there is a 18mm thick plastic spacer between the filterbox and the velocity stacks. All parts combined make a stack height of over 70mm which seems tall. The space between the top of the stack and the ceiling of the air box is 25mm which seems small.

Are there any downsides to just delete this plastic spacer? Stack height will be just over 50mm and the room between the box and the inlet will be well over 40mm.

Cheers,
william

William, the length of the inlet tract , which is from the back of the inlet valve to the end of the tract ie the top of the stack , is taken into account when tuning ,20mm doesnt sound like much but it would make a difference . There is a formula that gives minimum distance between end of bellmouth and the proximity to inside of plenum, cant remember what it was but its closer than youd think . Also any tuning should be done with the airbox lid and snorkles in place, they help to get cool air and taking them off only makes more noise.

The spacer was certainly added to optimize the power output curve. You'd have to put your bike on the dyno to see the difference w/ and w/o. I can imagine that the shorter distance between intake and airbox increases air flow velocity.

I decided to keep the spacer as I'm not smarter than Ducati. If leaving out a part would make it better than why fit it?

Think of the air going into your engine as balls of air that stimulate the carb to integrate the correct amount of fuel into the manifold, a smooth suck across the jet. What the spacer does is manage that ball of air so it's compact and even, if you take the spacers out, the ball of air will be created inside the filter which is jaggy on the inside this will create lots of turbulence inside your air ball. It will effect the air so it isn't smooth, this turbulent air will create an irregular "suck" on the jet making the fuel integration less smooth. The end result will be less power.

I hope this helps