| Author | Message | ||
     Gunslinger |
Maybe there is someone out there who knows more about fluid dynamics than I do (i.e. more than nothing). If I understand correctly, the stock air-box on my M-2 is a Helmholtz resonator. It boosts power by creating a pressure wave into the carb right as the engine starts its intake stroke. I see two issues here. First, in a V-twin, the two cylinders are pulling their charges of air through the box out of phase. A intake stroke starts on one cylinder, then the next is 405 degrees away, then the next is 315 degrees. I imagine the bright boys might have been able to allow for this, but it must be more complicated than in a straight 4 where the firing sequence is 180-180-180-180. The second issue I see, is that the boost would only happen at a certain "sweet spot" in the RPM range. So, how wide is the sweet spot? Also, is there a point where the resonance causes a drop in pressure at intake? While on the subject, does the condition of the filter have any effect? In case you have not guessed yet, I am contemplating the replacement of the stock airbox, and want to make sure I am doing the right thing. | ||
| Fasted |
before you rip the breadbox off, stash it somewhere out of the way in your garage and have it turn into a rodent condo (damhik), try the buellistic approach and modify it.......... | ||
| Gunslinger |
My biggest problem with the stock box is the complexity. It is a rather clunky thing too. Taking it off requires removing no less than 8 bolts and screws, including one of the breathers. The snorkel is a pain to get in place when re-assembling. Exposure to engine oil from the breathers has destroyed the foam seal around the edge. And , a crack has started where the two screws attach it to the front engine bracket. | ||
| 5liter |
I thought the Helmholtz resonator was there just to quiet down the intake. | ||
| Gunslinger |
That is one of the purposes, but supposedly on some engines it boosts performance. As you can see from my earlier post, I am skeptical of its overall value. I suspect the problems I have had with the foam seal and the cracking near the front engine mount are uncommon, simply because few Buells have hit the 55,000 mile mark with the stock air-box still in place. | ||
| Court |
I'll buy it from you. It's "power" is the result of what it does to the sound. IT produces no power, simply controls engine noise to allow the motor to make more power before reaching 80dB . . . kinda. | ||
| Gunslinger |
Mine is in pretty bad shape. What happened to yours? | ||
| Sparky |
Some Buells, well, my S1 anyhow, have gone way over 55k miles with the stock airbox.  | ||
| Gunslinger |
I have added some washers to bridge the crack, and replaced the foam seal with "Camper tape". The oil puking into the box liquified the original seal a long time ago. My biggest complaint is how much work it is to remove if you need to get at the carb, like the other night when my float stuck and flooded the engine. That is when I began wondering why I had kept it for so long. Do the "velocity stacks" built into some of the high-end air boxes really help? | ||
| Kalali |
I have the same question about my X1. Looks like the engineers spent a good deal of time designing the intake; the snorkel, the placement of the holes, etc. I thought it was supposed to "simulate" a larger area allowing more air into the motor thus a little more power/torque. Seems like a lot of work for just controlling the noise. | ||
| Court |
It has nothing to do with power. It was an elegant solution to an age old problem. P.S> - Be mindful that Helmholtz, although a Doctor of Medicine, did not have a Docrate in the Physics he so enjoyed exploring. The Buell airbox is essentially a Bose speaker turned inside out and 180o out of phase . . . (Message edited by court on April 12, 2009) | ||
| 5liter |
I know my "ham can" speaks to me when I really get on it.  | ||
| Kalali |
"It was an elegant solution to an age old problem." So could you please elaborate as what this "old age problem" is? Thanks. | ||
| Sparky |
The age old problem of getting a motorcycle to pass the required EPA sound (dB) tests required by manufacturers of all motor vehicles sold in the USA. The test has specific requirements that, I believe, include all noise from the engine and drivetrain from certain sides, right and left at specific rpms or speed. I believe that is why, on the tubers, the exhaust exits on the left and the air intake on the Helmholtz airbox aims to the left in order to offset the mechanical noise that the cam drive gear, engine fins and exhaust plumbing makes on the right side of the engine. So the objective for the Helmholtz airbox was to reduce the intake honk while having no reduction in performance over whatever the alternative would have been if there were no required noise limits. | ||
| Gunslinger |
I have been planning on getting a Hurricane unit through American Sport Bike. The Tax Man has delayed it a bit, but next month. It is a pricey unit, but everyone seems happy with them. I have been watching how much my stock airbox vibrates at various RPMs. At around 3500 it looks like it is moving over 1/4". I am surprised it has held up this long. | ||
| Myclone2 |
From my research the Helmholtz resonator works like a air spring and helps the engine breath better by utilizing the pressure waves created by the air bouncing off the intake valve as it closes catching it and bouncing the waves back to provide positive pressure for the next time the valves open therefore increasing the volume of fuel air mixture for the "suck" stroke of each cylinder. Its a performance feature. Eric B. wouldn't have gone to all the trouble to build a complicated set up just to reduce noise, That's a bunch of BS. Buells are relatively quite and you've heard Harleys? I imagine Eric Buell learned about the Helmholtz resonator as an engineer and utilized it as one of many tricks to increase the Sporty's HP output by 30%. 60 odd HP to 90+ HP along with the Thunderstorm heads, and lightened flywheel. I see everyone replacing them with aftermarket Sportster air cleaners or the Forcewinder style. You are paying to loose Horsepower. The exhaust is also balanced with the resonator and underslung shock for handleing and thats a reason not to change them either. The one improvement that is needed is changing the slow jet to the next size up 95 I'm pretty sure. It was jetted lean in order to pass EPA requirements and caused difficult cold starts and the irritating Keihin cough syndrome that the lean idle mixture created while closing the throttle in turns and such. Back to the breadbox, I love the sound it makes when you get on the gas. It sounds like some sort of snorting beast. Very Buellish. Following my research I am convinced that it works well. Here is a good video demonstrating Helmholtz resonators. https://youtu.be/PoEyIJx3uM0 | ||
| Myclone2 |
Looks like was a little late for the party.  | ||
| Panshovevo |
[ It has nothing to do with power It was an elegant solution to an age old problem. P.S> - Be mindful that Helmholtz, although a Doctor of Medicine, did not have a Docrate in the Physics he so enjoyed exploring. The Buell airbox is essentially a Bose speaker turned inside out and 180o out of phase . . . ] That cracked me up, Court. Thanks, I needed that. Not only am I a fan of Bose speakers, but I just spent all damn day installing the air box the previous owner took off of my X1W... (The S3T came with a carbon fiber ham can) | ||
| Myclone2 |
What is the age old problem your referring to? Please elaborate on the 180 degree out of phase. Out of phase of what? Peace Good read below. https://itstillruns.com/air-intake-resonator-do-12156112.html (Message edited by Myclone2 on November 26, 2019) |
