spacer between airbox and velocity stacks necessary?

discussions specific to the 906 Paso
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Fulvia-hf
Posts: 18
Joined: Sun Jun 06, 2021 1:19 pm
model: 906 Paso
year: 1989
Location: Netherlands

spacer between airbox and velocity stacks necessary?

Post by Fulvia-hf »

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
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Mc tool
paso grand pooh-bah
Posts: 1794
Joined: Wed Dec 05, 2007 12:35 am
model: 906 Paso
year: 1990
Location: Newzealand

Re: spacer between airbox and velocity stacks necessary?

Post by Mc tool »

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.
I wish I was young again............Id be heaps smarter than last time
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paso750
paso grand pooh-bah
Posts: 5505
Joined: Sun Jul 18, 2004 12:00 am
model: 750 Paso
year: 1987
Location: southern Germany

Re: spacer between airbox and velocity stacks necessary?

Post by paso750 »

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.
Fulvia-hf
Posts: 18
Joined: Sun Jun 06, 2021 1:19 pm
model: 906 Paso
year: 1989
Location: Netherlands

Re: spacer between airbox and velocity stacks necessary?

Post by Fulvia-hf »

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?
Stepaso
Posts: 14
Joined: Sun Dec 29, 2019 11:30 pm
model: 750 Paso
year: 1988
Location: New Zealand

Re: spacer between airbox and velocity stacks necessary?

Post by Stepaso »

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
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