On the intake hose for a 2001 Honda Prelude SH there is this U shaped tube with one closed end (sorry about blurry shot):

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(The tiny thing sticking up on the top left isn't a tube it's just a solid structural support piece.)

The part is only identified as "TUBE, SIDE BRANCH". It's also discontinued for some reason:

enter image description here

What does this tube do, exactly?

Some clarification from comments; here is where the throttle / MAP sensor / intake manifold is in relation to this:

enter image description here

  • 1
    Its a silencer for intake noise. – Moab Aug 6 '16 at 0:56
  • @Moab Huh. How does it silence the noise? – Jason C Aug 6 '16 at 0:58
  • Ask the engineer that designed it, these are common on cars since the 1980's, they come in all shapes and sizes depending on what software or engineer designed it. The bigger the engine the bigger the silencer typically. – Moab Aug 6 '16 at 1:15
  • 1
    Related question – Zaid Aug 6 '16 at 18:08
  • 1
    A Helmholtz resonance related question – Zaid Aug 6 '16 at 18:11

It's a silencer. It's used on the intake tract to deaden the noise of the air as it goes through the intake. It usually isn't needed, but if taken off, you'll need to ensure the hole is completely plugged. If you don't, unfiltered air will enter your intake and cause issues.


For more information on the phenomena of how the silencer (resonator) does it's thing, this question was asked on Physics.SE.

  • I think the prelude is a speed density setup. – Ben Aug 6 '16 at 14:49
  • @Ben ... you could be right ... I'm not seeing a MAF in the diagram, I guess I'll update accordingly. Thanks! ... EDIT: Updated. – Pᴀᴜʟsᴛᴇʀ2 Aug 6 '16 at 14:51
  • I've been doing some research on this and, it's a little unclear to me, but it seems to be referred to i general physics discussions as a type of Helmholdtz resonator called a "side branch resonator". Also it looks like it serves both as a silencer and also has something to do with preventing back pressure from harmonics when the intake valves close. So some descriptions suggest it helps maintain good intake pressure and is part of maintaining engine performance. Do you know anything about this? I'm still researching. – Jason C Aug 6 '16 at 15:05
  • As for the prelude, if it means anything, it has a MAP sensor, near the throttle body, it's the next thing on the downstream side of the pictured intake tube, it's immediately adjacent to the right side of the tube. It's not in that parts diagram, its in a different intake manifold parts diagram. Hose clamp 13 connects to the throttle body, sensor, and manifold. – Jason C Aug 6 '16 at 15:07
  • @JasonC - It sounds at least reasonable about it being a resonator. I think I am using "silencer" and "resonator" interchangeably, though that could be a wrong notion. And as far as the MAP, are you suggesting #25 in the diagram? Or #4? If the MAP is upstream of the resonator, it would cause fueling issues to not seal the hole, as the computer would not be getting the correct pressure readings. – Pᴀᴜʟsᴛᴇʀ2 Aug 6 '16 at 15:11

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