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916 Early Air Intake Tubes

Discussion in '748 / 916 / 996 / 998' started by Chris 748SP, Jun 29, 2020.

  1. 1)Does anybody know the difference between the early Pre 97 ish air intake tubes on the 916/748 and the updated version. I’d it just a metal anti crush collet on the screws? There’s 2 different part numbers anyway.
    2)What was the purpose of putting the rubber air destructors found in some later models?
    I’m sure somebody will be familiar with it.
     
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  2. Pass, sorry! :)

    I think the blocks you mention might be the restrictors? These always ended up in the bin at the first opportunity
     
  3. Were these the Varese tubes?
     
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  4. I have some December 1994 Airtubes from a 916 lying around. If you want some pictures let me know.
     
  5. Ha ha. Not all Varese, some Bolognaise ones too. Yes tubes were different part numbers on the first 5 thousand or so. There’s something different for sure.
    Yes it’s the rubber air restrictors (auto spell mistake) on the later ones that I wondered why they went in.
     
  6. Can’t remember now but I think they were for noise dampening.
     
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  7. 1) The early bikes connect the two air tube halves by using bolts that screw into a brass nut encased in rubber. Part # 75040051A.
    It was a design flaw- they rip the rubber too easily (hence the change to screwing straight into the plastic on later bikes ).

    2) They reduced the intake roar to pass EPA noise restrictions.
     
    #8 TNR, Jun 29, 2020
    Last edited: Jun 29, 2020
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  8. The rubber restrictors were there to cancel out the Helmholtz effect of the intake tubes. Here's a brief description of what they were meant to do. I went to Neil Spalding when he used to run his Ducati business and he told me what they were for and that there was no problem removing them etc. and recommended that I do that. This was on my 998 when it was new.

    Helmholtz Resonance. A Helmholtz resonator or Helmholtz oscillator is a container of gas (usually air) with an open hole (or neck or port). A volume of air in and near the open hole vibrates because of the 'springiness' of the air inside.
     
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  9. £££££ :bucktooth:
     
  10. @Akorenika, thanks for the offer but I have an early set here. I would like to replace one outer cover but wonder why there are 2 part numbers as I can’t see the difference on photographs.

    @Red998 thanks for the Helmholtz info. Suppose with circa 22,000 litres of air travelling through the air box every minute at 12k revs there will be some resonance in the tubes but it must be for fuelling not noise...can’t say I’ve heard any resonance. Anyway, it’s all too complicated for me but thanks for the info.
     
  11. You should definitely hear the Helmholtz effect on acceleration. It's unmistakable.
    Sounds like a jet taking off to my ears.
    Here's some more info on what is and why it's important.

    "Another source of glorious racket, the intake roar of an early Superbike is truly awesome. Pre-996 models (916-748s) had unrestricted intake runners that generate a phenomenal roar from around 4500 rpm up. This is the airbox resonance effect, sometimes called Hermholz resonance; it’s the sound of the air alternately pounding into and getting pushed out of the airbox by the ram-air and intake effects. It’s a good noise, it means the intake is working properly. 996 and later models had rubber venturi blocks inserted into the intake runners after the air filters to dampen the noise – if you want the full noise effect open the runners and pull the restrictors out. Alternately if you don’t like the noise buy some restrictors and put them in."

    https://www.odd-bike.com/2013/01/ducati-desmoquattro-superbike-faq.html?m=1

    One day recently, the intake roar on my bike disappeared. Looking at the air tubes once I got home, I could see big cracks in the runners. The rammed air was going straight thru the cracks, and not pressurising the airbox as it should.

    The reason? The rubbish early air tubes!

    2020-06-30 20.31.13.jpg

    Seeing as it appears to be early 916 geek week, I just changed all of mine out so you can see the difference if you have a later (post '96) bike.

    Here's the bolt and new nut:

    20200630_173412.jpg

    And what happens to the old nuts over time... you turn the screw but no way for it to tighten.

    20200630_173107.jpg

    Pull them all out and push in the new ones, screw back together.

    Will go for a ride tomorrow and see if the 'glorious intake racket' is back!
     
    #12 TNR, Jul 1, 2020
    Last edited: Jul 1, 2020
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  12. Perfect TNR. I’ve never had a later bike with the rubbers in so never heard the difference. Your post also answers what the difference is on the early runners too. The rubber Wellnuts. Thanks
     
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