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Interesting Configuration

The Yamaha R1 has a very strange intake design. Notice the intake horns in the image below. They sit above the throttle bodies and are not attached directly to them leaving an air gap between the throttle bodies and these horns.

If the full assembly were visible this would all be shrouded in an airbox.

My Questions

Why are they doing this?

What are the benefits of the intake horns sitting above the throttle bodies with a gap between them?

Could this be a method to reduce resonance within the airbox at high RPM running?

enter image description here

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2 Answers 2

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This is a variable-length intake

Variable-length intakes increase the pressure of the air entering the intake manifold thanks to a physical phenomenon called Helmholtz resonance.

It's also known as dynamic supercharging since it avoids the use of a mechanical device (compressor/blower) to boost intake air pressure, which means the air enters the cylinders at a higher pressure. Needless to say:

▲ Air Pressure → ▲ Bang → ▲ Torque → ▲ Power

How does it increase air pressure?

Any air intake geometry has a certain Helmholtz frequency associated with it, just like how blowing over the neck of an open bottle produces a certain note or pitch.

At this frequency, the air molecules vibrate more, resulting in higher pressure.

So why does varying the effective intake geometry help?

Engine RPM will govern how often the intake valves open and shut. These valves generate pulses that translate to a frequency signature.

The idea behind varying the effective geometry is to get the Helmholtz frequency of the air intake to sync up with the frequency demanded by the engine over a range of RPMs.

This setup alters intake runner length

Much like how the Le Mans-winning Mazda 787B did.

The neat thing about this setup is its relative simplicity and robustness. Consider the 787B's trombone-like intake runners. The sliding motion between the two concentric pipes might be good in the short term, but I struggle to see how any mass-produced vehicle would feature this design; the interference between the two parts would require something special to last for an acceptable amount of time.

Which is why the setup in this Yamaha is sheer genius; it does away with the interference altogether while maintaining the benefits of the variable-length setup.

It's like an invisible, flexible wall. Awesome engineering!

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  • so this is designed to create resonance rather than suppress it in order to get a better intake charge and increase the volumetric efficiency?
    – DucatiKiller
    Commented Jan 27, 2016 at 19:37
  • @DucatiKiller It's taking advantage of the resonance that exists at any given RPM and lines up the intake to match that resonance frequency.
    – Zaid
    Commented Jan 27, 2016 at 19:38
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    That's beautiful. Using the resonance in your favor and looking at it as a tool rather than a pain point.
    – DucatiKiller
    Commented Jan 27, 2016 at 19:39
  • Yup, that pretty much sums it up
    – Zaid
    Commented Jan 27, 2016 at 19:40
  • I'm going to edit your answer so it goes back in the feed. It deserves as many votes as my question, actually more.
    – DucatiKiller
    Commented Apr 1, 2016 at 21:47
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The 'floating' intake runners are moved by a mechanism, coupling and decoupling them from the main intake runners to increase the overall length for better low RPM performance. This process was recently discussed here:

mech.SE on inlet runner length

I don't see that having the extension pieces in the decoupled position would have any effect of the resonant properties of the air box, particularly as they have open ends.

Here's a couple of pictures of another, very similar, Yamaha system shown in both states: enter image description here enter image description here

This is an article from Yamaha that explains the system and the purpose of it.

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  • Interesting. nice simple answer. thank you. Do have anything that shows the actuation or a citation perhaps?
    – DucatiKiller
    Commented Jan 27, 2016 at 9:17
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    @DucatiKiller I've tried to explain the how in my answer to this question.
    – Zaid
    Commented Jan 27, 2016 at 9:40
  • @DucatiKiller Photos and link to Yamaha article provided.
    – Sam
    Commented Jan 27, 2016 at 15:03
  • Yes, short but sweet article. Read that last night before I asked the question. From the sounds of it this is to prevent high RPM resonance waves from interfering with the intake charge. Interesting technology.
    – DucatiKiller
    Commented Jan 27, 2016 at 17:58

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