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Does anyone know what throttle opening is possible in neutral and mode 2?

I just did a very quick differential pressure measurement when I got back from a ride and got a reading of -0.003psi in neutral and hitting the rev limiter. I guess that the ecu is not allowing full throttle in neutral + mode 2 but nonetheless, that reading seems far too small. The meter’s minimum step is 0.001psi and max reading is +/-1.5psi.

I was expecting a fluctuation between -0.1psi and 0 (atmospheric), maybe even +1 to -1 at resonance if that theory is correct.
 

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Thanks. Do you know if these throttle maps have been shared anywhere?

80% suggests my quick n easy test was flawed, or my thinking is, or both.

I had figured I'd need to rig up measurement tubing in fixed positions in the airbox,and go for a 3am rides at full throttle in 4th or 5th gear... this would be the only way to get accurate real-world readings.... but I didn't think the static test would be a bust, so now I'm wondering if I'm going to be able to get useful or even reliable data.
 

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Hi,

I think I'll have to give up trying to measure resonance pressure - I checked my manometer with a simple Boyle's law test using a syringe - decrease the volume by 10% and the pressure went up 10%, so it works; however, it has significant lag between the change in pressure and the change in reading so I think it is heavily smoothing. It's a Benetch GM510. That means it won't be able to display the rapid pressure fluctuations at resonance - they are expected to fluctuate equally above and below the prevalent pressure at very roughly 70Hz or so, so the reading will just show the average, not the fluctuation, effectively ignoring the excitation at resonance. As a result, I won't know if it has changed due to modifying the box. The meter will only be useful for measuring non-resonant pressure for an opened box with no resonance. Meh.

However, the three airbox intake pipes are the equivalent of three round pipes of diameters 40mm, 45mm and 50mm and their lengths and airbox volume set their resonant frequencies within a narrow range (+/-10% of the combined fundamental) and, as such, they'll be interacting with each other to spread the boost over that range. Back of a beer mat calculations suggest they boost flow around 2,500 to 3,000rpm, not the 4,000 or 5,000rpm I expected. And here's the kicker - if the resonance is set at such a low frequency/rpm, then the engine isn't producing much vacuum pressure, so the resonance hasn't got much energy to amplify.

This means cutting the tubes down in length would lose only a little torque at the bottom but could add much more higher up where the engine is creating much more vacuum pressure. Robbing Peter but Paul gets paid twice :)
 

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Hi,

I think I'll have to give up trying to measure resonance pressure - I checked my manometer with a simple Boyle's law test using a syringe - decrease the volume by 10% and the pressure went up 10%, so it works; however, it has significant lag between the change in pressure and the change in reading so I think it is heavily smoothing. It's a Benetch GM510. That means it won't be able to display the rapid pressure fluctuations at resonance - they are expected to fluctuate equally above and below the prevalent pressure at very roughly 70Hz or so, so the reading will just show the average, not the fluctuation, effectively ignoring the excitation at resonance. As a result, I won't know if it has changed due to modifying the box. The meter will only be useful for measuring non-resonant pressure for an opened box with no resonance. Meh.

However, the three airbox intake pipes are the equivalent of three round pipes of diameters 40mm, 45mm and 50mm and their lengths and airbox volume set their resonant frequencies within a narrow range (+/-10% of the combined fundamental) and, as such, they'll be interacting with each other to spread the boost over that range. Back of a beer mat calculations suggest they boost flow around 2,500 to 3,000rpm, not the 4,000 or 5,000rpm I expected. And here's the kicker - if the resonance is set at such a low frequency/rpm, then the engine isn't producing much vacuum pressure, so the resonance hasn't got much energy to amplify.

This means cutting the tubes down in length would lose only a little torque at the bottom but could add much more higher up where the engine is creating much more vacuum pressure. Robbing Peter but Paul gets paid twice :)
You should read some of the early promotional materials about the design of gen3 air box ,yamaha was bragging about bringing the engineers over from the music side of the company ,to make the air intake noise sound better
 

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Yes! There was a video that I particularly enjoyed.... (1) 2021 Yamaha MT-09 – Sound enhancement - YouTube but I am cynical enough to think that such stuff is part of the marketing because Managing Noise to Please the Man is a major part of the development.

What the video doesn't say is that the cam chain is noisier than ever because the reduced overlap (to reduce emissions) required steeper cam ramps to maintain volumetric efficiency, and that resulted in a wider stronger cam chain and an oil-pressure driven tightener. I'm sure I'm not the only one who's noticed how much chain noise this bike makes. I tried 85W-140 GL5 gear oil on the drive chain rollers and sprocket teeth and that killed the drive chain noise for 50kms until it had come off.

Still, fascinating airbox design eh?

EDIT - I looked up EURO 5 noise but couldn't find the latest - perhaps that part has not been legislated yet. However, I did find that EURO 4 was 80 dBA and the recent proposal is to reduce that to 77 dBA for large capacity motorcycles (L3E-A3 category).

Because of the nature of air mass in a pipe, a longer pipe does a better job of suppressing frequencies above its resonance - the higher the frequency, the more it is suppressed. IDK which, but the suppression is either 6 or 12dB per octave, not that this matters. So, the longer the pipe, the lower the pipe's tuned resonance becomes, and the less high rpm induction noise comes through. Longer is quieter basically.

I also calculated if one pipe could replace the three - it's very rough because I haven't measured airbox volume yet, but it would be a pipe with a diameter of 7.7cm and 60cm long. Quite impractical. I think this shows why multiple pipes might become increasingly common.
 

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I also calculated if one pipe could replace the three - it's very rough because I haven't measured airbox volume yet, but it would be a pipe with a diameter of 7.7cm and 60cm long. Quite impractical. I think this shows why multiple pipes might become increasingly common.
I am getting old... I forgot that using multiple ports on a subwoofer means the ports need to be longer for the same frequency than if using one port ... so 60cm is incorrect - it can be about half that. The exact dimensions needs a Fourier analysis, which I am not smart enough to do, so I use online calculators.
 

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I got a reply from DNA -
The number you are looking for is completely theoretical and can not be achieved on the stock half airbox (bottom part) in place "
So I've been doing more reading on how resonance is used to boost flow into the engine, and the main factor is the inlet tract of the engine - from the intake valve, up the intake tract, through the throttle body and then the intake stack that draws air from the airbox - resonance here is key. So it has finally dawned on me what DNA meant by saying that "the bottom of the airbox" is the limiting factor - they meant those intake stacks at the rear of the airbox. And from what I've read, these are definitely the leave well alone parts - major changes (cams etc) would be required if these were altered in any way. This article is an example - dunno if you guys can access it - you might need a university library account to read it. Combined Effects of Variable Intake Manifold Length, Variable Valve Timing and Duration on the Performance of an Internal Combustion Engine (silverchair.com) This is also good. https://julac-cuhk.primo.exlibrisgr...07&institutionId=3407&customerId=3405&VE=true and so is this [PDF] Effects of variable-volume Helmholtz resonator on air mass flow rate of intake manifold | Semantic Scholar


So, I have one more number to add to the collection of data - max flow is limited to about 150CFM - and that means about 50% more intake area is needed - about ~7,300mm2 in total - a 10cm or 4" diameter entry point. If I next measure volume of the airbox, I can calculate port length to tune the intake of box to a particular resonant frequency/rpm.
 

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Thanks for the offer, and also thanks for posting your dyno results on your site. I've got a lot of useful info from them :) I wish I had access to a dyno here but the only one closed down last year. It means I wont be able to prove any mod is successful, or use a dyno to develop a mod. I'm stuck with less reliable, less detailed and more difficult ways - basically reverse-engineering the box and seeing if there's way to maintain resonances but increase intake area and find a way to get cooler air into them. .
 

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I found the closest equivalent research that I think I'm ever going to find - it's a study on changing the airbox parameters such as inlet diameter and length, Helmholtz resonators, etc. with the intention of optimising noise but while also measuring power and torque to find a compromise. They did simulation and real-world and found the sim to be accurate to within 2% of the real engine. The test engine is 1.6L 6,000rpm normally aspirated 16 valve 4-cylinder - that's theoretically only 10% more CFM than an 890cc 10k rpm, - and 4-cylinder instead of 3 only means a proportionate shift in resonant frequencies.

tldr - larger diameter tubes will flow more and produce more power but also more noise, and the resonant effect of the airbox intake snorkel is not that significant in boosting power because they are long in order to suppress noise. It's the inlet tract design that creates the biggest resonant boost.

MohdFaridSaid2019_AcousticStudyofanAirIntakeSystem.pdf (utm.my)

Here's airbox pressures - it's close to atmospheric (1 bar) at idle and drops to 0.985 and 0.98 bar at 6k rpm. The vacuum effect is larger on the engine side of the air filter due to the restriction of the filter.
Rectangle Slope Font Line Parallel

Longer airbox intake snorkels primarily function to lower noise (and the 890cc airbox has some of the longest intakes I've seen on a larger capacity bike) but they also affect power/torque - longer produces slightly lower top end power and shifts the resonance boost to a lower rpm. This is also confirmed by Vcyclenut's dynos.

Rectangle Slope Plot Font Line

Here's David's dyno run of the stock versus cut down tubes and removed top with DNA air filter. Note the loss at 2,800rpm - the original resonance - and the boost at 4,200 - the new resonance of the shorter tubes. Slight increase in top end but the lower resistance of the DNA air filter is helping the modification show gains at the top end.
Rectangle Slope Plot Font Line

This is the length of tubes that created the 4,200rpm boost - without the top section, they are all quite similar length.
Wood Floor Flooring Gas Hardwood


Finally, here is the effect of larger intake diameter on power and torque. The research paper also shows that a larger intake diameter is also noisier, so the authors of the report recommended the 50mm pipe not the better performing 60mm because noise was significantly better.
Slope Rectangle Plot Font Line

So what does this mean for modifying the airbox?

That depends on the project's objectives, and tools available. For me, I'm going to look into enlarging the intake area and leaving myself with two options - 1. standard resonant frequencies but with 50% or more extra flow and 2. also 50% more flow but move the resonant frequencies to about 6,000rpm so the boost enables a broader peak torque plateau. The latter option will require a dyno. Not sure how I can do that since there isn't one here, but I'll look into some way to solve that.

For option 1, the three OEM airbox intake pipes are roughly equivalent to 40mm, 45mm and 50mm diameter pipes.

If DNA’s numbers are correct, then the box needs 50% more flow. This means the 40mm becomes 48mm, the 45mm becomes 55mm and the 50mm becomes 60mm. Other sizes/combos are possible too of course. But let's say it means keeping the largest pipe (but it becomes the smallest), removing the two smallest pipes, and fitting 55mm and 60mm pipes in their place. 55mm is not common, so if the pipes all became 50mm in diameter, the increase in intake area would be only 25%. If one replacement is 50mm and the other is 60mm, the increase is 41%. Using two 60mm replacements and the smallest pipe will result in a 50% increase, .... if the larger sizes can both fit. Then the questions are what length, and can they fit in the box and area around it.

Length is determined by airbox volume, so measuring that is the next step.
 
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