airbox mods - - The Ultimate Ducati Forum
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post #1 of 20 (permalink) Old Apr 16th, 2006, 6:11 pm Thread Starter
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airbox mods

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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post #2 of 20 (permalink) Old Apr 16th, 2006, 8:10 pm
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airbox mods

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;

"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;

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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post #3 of 20 (permalink) Old Apr 17th, 2006, 8:01 am
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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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post #4 of 20 (permalink) Old Apr 17th, 2006, 9:15 am
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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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post #5 of 20 (permalink) Old Apr 17th, 2006, 11:18 am
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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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post #6 of 20 (permalink) Old Apr 17th, 2006, 11:56 am
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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.

Can't get a new sig pic to load. Oh goodie.
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post #7 of 20 (permalink) Old Apr 17th, 2006, 4:03 pm Thread Starter
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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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post #8 of 20 (permalink) Old Apr 17th, 2006, 8:21 pm
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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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post #9 of 20 (permalink) Old Apr 17th, 2006, 8:29 pm
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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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post #10 of 20 (permalink) Old Apr 17th, 2006, 8:54 pm
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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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