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Discussion Starter #1
I'd like to start a thread to discuss the relative merits of various airbox modifications. How about a general discussion irrespective of various models.

1) Cut out top of airbox to get more air
One of the first mods I have read many owners performing is the cutting out of the top of an airbox. I've even seen dyno runs stating that this is capabile of making more power.

However, this goes against everything I've read about the benefits of airbox/plenum chambers, and should actually make less power than if enough air is available in the first place. Technical papers compairing individual intake runners exposed to open air vs. using a common plenum chamber show a "properly engineered" plenum chamber makes more power every time.

Perhaps since we may not have a "properly engineered" air box, the easiest thing to do is chop it up, but I wouldn't think this to be the optimal solution. More about this below.

2) K&N or other aftermarket air filter
While many aftermarket air filters can flow more air than stock, from what I've seen they also let a lot more crap into the intake than the oem paper filter. Perhaps the filter is not correctly sized for the application.

3) Enlarging air box volume
Much debate exists in this area - I've seen recommendations anywhere from the volume needing to be between 100% and 500% of the engine volume. I haven't seen any actual tests with respect to Ducati motors.
It would be very nice to see air box volume increased and decreased in dyno tests (with appropriate fueling changes).

4) Modifying size/length/number of airbox inlet resonators
It's my understanding these only exist to quiet the airbox. I haven't seen dyno tests of removing these, adding additional resonators or changing their dimensions.

So, can we spark some debate and discuss to shed some light on the subject(s)?
 

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No personal expertise but I've read of airbox mods from these two sources:

here's a little something from Neil Spalding at Sigma Performance;

http://www.sigmaperformance.com/st4.html

"A couple of interesting asides came out of these runs. A standard Ducati air filter causes no measurable restriction at all; at least we couldn't measure any difference. The open pipes are worth 2 to 3 bhp all the way from 3000 to 9000 rpm they then hang on to the top end better with 110 bhp from 9000 all the way to 11000. There were very few mixture differences with the airbox modifications, if anything we were a little lean with the intact box and then saw a slightly richer mixture with the final mods to the box; go figure."

and this from Moto-One;

http://www.moto-one.com.au/performance/888.html

I best get back to finsining a cover letter, application, and resume. I'll let the .ms engineers duke it out. dup!
 

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I went the open box (aluminum retaining ring) / K&N route on my 750. Maybe a little more power, but A LOT more noise. The sound is cool in a way, but also potentially harmful if you don't wear ear plugs. I recently put the lid back on just to protect my hearing. Not worth going deaf for a few hp.
 

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Ah, yes... the "cheap mods = big gains" concept. Always intriguing. And a great source of advertising grist. These threads typically provide far more heat than illumination.

Good links to Sigma, Moto One. See Doug Lofgren's site also.

Google the topic and you'll find all sorts of claims of big gains due to even the slightest of airbox mods. And pay particular to quotes which say something to the effect of "we didn't notice much change on the dyno, but the seat of the pants told us otherwise." LOL

BTW, a big +1 to the unnecessary noise caused by airbox mods although noise-induced fatigue is a greater danger than deafness, IMO.
 

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I've had a closed airbox (sucks, technically doesn't), open air box and now pod filters on my S4. Open airbox allows more air (and sound) for more HP. May/will need to retune bike. Pod filters didn't affect Hp (within 1hp of open), look cool and are loud (also have to put a K&N crankcase filter on).

closed airboxes are meant to keep sound low, like stock mufflers. Not the best but work. If you can handle open exhaust and clutch covers then you can handle a open airbox/pod filters.

If HP is your ultimate goal, buy a Japanese bike.
 

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I saw a dyno chart of the benefits of the open airbox mod with ST bikes, but I've heard that it robs HP from superbikes. I don't know of any of the other bikes.
 

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Discussion Starter #7
I've been reading a number of SAE papers (crazy I know, I'm just curious), and just cutting open a plenum chamber in order to get more air in it just seems like exactly what it is: hacking.

I believe that since some bikes with some modifications are seeing an increase in hp when hacking up the airbox is a very clear indication that the stock airboxes are not well engineered for performance - perhaps space constraints were a major factor.

The airbox should be acting as a plenum chamber offering helmholtz resonation within a defined rpm range to help fill the cylinders beyond basic atmospheric pressure. You will see this in almost any modern racing or road car. The research I'm reading shows a clear 6-10% increase in cylinder filling capability with a properly designed plenum chamber over relying on atmospheric pressure alone.

By hacking out 1/2 or the entire top of the airbox, the plenum chamber is being removed, and we are going back to basic atmospheric pressure. Why not size the plenum chamber inlet size appropriately to flow the required CFM, and then size the internal volume properly for the engine requirements?

There is no reason this cannot be accomplished while keeping the noise level low. These hemholtz resonators are actually quite effective at noise reduction, they just may need to flow more, or additional inlets added to achieve necessary CFM.

I would think that with the possible gains in this area, there would be much more information available as applied to twin motorcycles in the public domain. I'm still searching for it.
 

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The dyno graphs on Brad Black's site show clear hp gains from the open airbox mod on just about every 2-V ducati he has tried it on. Hard to argue with the dyno data.

But still not worth the noise IMHO.
 

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I think there are some misconceptions going on...but I'm no expert either....Anyways my understanding of the Helmholtz wave and plenum size/design is that they are only a factor in intake charge when considered AFTER the throttlebody. Prior to the throttle body the concern is primarily not restricting the airflow by creating a plenum that doesn't flow or restricting cross sectional flow. In my opinion, the SS airboxes are NOT plenums at all, from the designed inlet/outlet positions and overall shape there appears to be no acceleration or even significant redirection of airflow. (I could be wrong). I think in the SS case less restrictive is better. (monsters as well, don't know about SBK's). Oh, and I like the extra noise from the intake and I almost always wear earplugs..intake honk is nothing compared to hours of wind noise...
 

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I agree that a well designed airbox will add power, with the use of Helmholtz resonance tuning - the problem is that it tends to be concentrated in a very narrow RPM range. I've often seen a secondary wave tuning affect at a much lower RPM, which also helps the power down below, but this also often results in a dip in VE between these two peaks.

Still, overall, a properly designed airbox of sufficient volume and rigidity and intake area/design can and does perform better than an "open air" design, and with significantly less noise.

This doesn't mean that there aren't specific cases where the airbox is so poorly suited to it's motor, or is so restrictive, that chopping it up and opening it to become a quasi open-air design doesn't improve the performance - clearly there are cases where this results in better breathing, but that doesn't mean that a completely different and better designed boc can't improve the power even further on that same motor! ;)

Additionally, the use of a sealed rigid airbox allows the use of the cold and ram-air intakes, which further improve efficiency - something that open intakes or open airboxes generally can't do, due to their location.

The latest Japanese sportbike boxes are much better designed than the old bikes of 20 years ago - and take up a huge amount of real estate, compared to the older designs, requiring all sorts of changes to motorcycle packaging.

This is a subject that I'm real interested in, and will be pursuing further as soon as I can find a decent deal on the extensive dyno tests needed to test the effects of alternative volumn airboxes on my Duc.
 

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Some more bread crumbs; I think it was the 2nd F1 race this year that a F1 race car commentator pointed out the location of the airbox or possibly some high tech apparatus on one of the F1 cars (he brought it up as to whether is within the rules) as the other cars didn't appear to have it way out on the front wing like this car did. Anyway then the other commentator said heck ya it's an advantage as the motogp bikes found the airbox gains were the single greatest gains, like extra 10% or whatever. Not 100% it was 10% but it was a big increase. Sorry not much fact in all that fat but you get the gist of it I hope.
 

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an airbox may play a significant role with superbikes but with Monsters it's more of an afterthought. Look how the new S4RS loses HP to the 999s because of it's small air box and injection.
 

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For the SBKs what are the airbox options? I have seen the larger corse boxes which are tight to fit into the frame. Different air filter options. Pipecross, ITG (which I have and getting rid of since I have found that it takes up too much space.) BMC or MadDuc. I am considering the MadDuc filters they are inexpensive and seals around the intakes. In my little research I have found on the SBKs the ram air does is job and then you want the largest volume airbox to create a venturi as the air enters the intakes. The ITG (large foam filter that fills the airbox) type filters seals from any debris from entering the intake, but also disrupts the venturi effect of the air entering the intakes.
 

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The Ducati Performance kit for the ST series comes with an open airbox lid. Why would Ducati sell this if they didnt think that it made a difference? I think this is a great thread, it is gret reading everyones input!
 

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st4spokane said:
The Ducati Performance kit for the ST series comes with an open airbox lid. Why would Ducati sell this if they didnt think that it made a difference? I think this is a great thread, it is gret reading everyones input!
Because it probably does! :)
 

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Synergy said:
For the SBKs what are the airbox options? I have seen the larger corse boxes which are tight to fit into the frame. Different air filter options. Pipecross, ITG (which I have and getting rid of since I have found that it takes up too much space.) BMC or MadDuc. I am considering the MadDuc filters they are inexpensive and seals around the intakes. In my little research I have found on the SBKs the ram air does is job and then you want the largest volume airbox to create a venturi as the air enters the intakes. The ITG (large foam filter that fills the airbox) type filters seals from any debris from entering the intake, but also disrupts the venturi effect of the air entering the intakes.
There are a coupla large-box options, that place the TBs INSIDE the box, which extends down much further into the V of the motor - allowing for much larger volume. Veetwo and EVR have a coupla examples....and there are others around.
 

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OldBaldy said:
There are a coupla large-box options, that place the TBs INSIDE the box, which extends down much further into the V of the motor - allowing for much larger volume. Veetwo and EVR have a coupla examples....and there are others around.
Also adding to what I said...helmholtz wave is only a significant factor AFTER the TB's. Since the TB opening is the restriction, it is the "effective end" to a pulse wave seen/generated by the cylinder...."ram air", turbo, supercharging all pressurise an intake prior to the trottlebodies..this pressurization would negate/eliminate any wave pulse yet it still improves performance...
I simply cut away most of the cover leaving a "scoop" at the aft end....probably of no real benefit over a straight open top, maybe when pulling tripple digits.....
 

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sk66 said:
Also adding to what I said...helmholtz wave is only a significant factor AFTER the TB's. Since the TB opening is the restriction, it is the "effective end" to a pulse wave seen/generated by the cylinder...."ram air", turbo, supercharging all pressurise an intake prior to the trottlebodies..this pressurization would negate/eliminate any wave pulse yet it still improves performance...
I simply cut away most of the cover leaving a "scoop" at the aft end....probably of no real benefit over a straight open top, maybe when pulling tripple digits.....
Nope - the Helmholtz affect plays a role before the throttle body as well - including the airbox and intake runners, but only when there is a closed, rigid system. It's part of the reason those big in-box filters kill power in the SBK (there is no reduction in raw CFM flow, but there very definitely is a smothering of the wave pulse).

The wave formation runs from intake valve right back to the end of the intake system. Clearly, this has greater affect at WFO, where the TB plate is not closed off :) but it it still very much plays a tuning affect on the intake system.
 

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Discussion Starter #20
Curiosity got the best of me, and I've made some measurements and calculations on the ST3 airbox. (ST4s may be the same, but I don't have one to measure).

Airbox volume is ~ 6.7 liters.
This is larger than I expected since it looks so small. Of course the filter takes up some of this room, but I haven't taken that into account.

The intake snorkel measurements are:
28mm small external airbox intake end
40mm at larger internal airbox end
116mm total length

side note of interest: I learned something new today - "you might assume forward-facing intake made in the form of a funnel would multiply the pressure of the air, resulting in a much larger pressure gain at the small end. Sadly, intuition is wrong. In order to convert velocity energy into pressure, the air has to be slowed down, and this requires a duct that widens rather than narrows." This is validated by almost all modern competition airbox designs.

Calculating the airbox resonant frequency of this combination:
(0.5 * C )/ (Pi * sqrt( S / ( L * V))
Where:
C = speed of sound ~ 340 m/s
P = 3.14
S = area of port
L = length of port (there are some end effects we're ignoring for now)
V = air box volume

Gives us 49 Hz, which equates to just about 3000 RPM.

We could theorize that Ducati selected this RPM for meeting noise regulations, however I'm sure it also extends the torque of the engine at the bottom of the operating range.

I will first try and move this resonance area up to 67 Hz which is about 4000 RPM. This will be accomplished by enlarging the area of the port by 2mm, and shortening the length of the ports by 46mm.

While a dyno would be very nice and the only way to really test the change, I'll be using a combination of seat of the pants feel, as well as a microphone measurement of resonance vs RPM.

A question for you technical types which I haven't been able to locate the answer to: Does adding additional (and equal dimensioned) helmholz resonators to a cavity change the fundamental resonance frequency? Perhaps the frequency remains the same, but at a lower pressure?

I would like to continue to add airflow capability without changing resonance characteristics.

Enough theory - where's my hacksaw :)
 
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