air box stories

Sorry guys for that global shortage in RC8-stacks, When it became obvious, that these stacks are the best bang for the money, I ordered the whole batch early this year, the KTM factory had in stock.

Of course I am monitoring the A/F-ratio when I do any testing on the dyno. And in fact changes of the A/F ratio indicate very precisely if any mod works or not. We are talking here about fuel injected bikes. Here the ECU acts like a robot and executes according its internal map the fuel supply. A carburetor would act much more sensible and smarter to potential changes within the air flow thru the engine, and if it is "well jetted", it may adjust itself "automatically" to a mod, i.e. a new header - not necessarely, but there is a good chance, if that mod do not alter the air flow thru the engine too dramatically..

"Power is nothing but air and fuel", to cite an old DYNOJET slogan. So in the case of an ECU-robot, handling the fuel supply for an engine, as long as the mappings remain unchanged, if there an mod is able to create a "lean situation", it simply works, lets the engine breathe better and makes more power. And vice versa: Any drop within the monitored A/F-ratio within any range of the power band is the proof, that a modification sacrifies engine charge and volumetrics.
Simply because that A/F-stuff means a ratio, in the case of a robot-ECU, during testing a mod on a dyno, the fuel supply as one factor of this ratio is fixed.

My own experience with the RC8-stacks shows, they make real and substantial power , up to 5% gain from 7000-7500 upwards. Of course to release that potential into real power at the rear wheel, some mapping MUST be done to adopt the A/F-ration accurately to that new volumetrics, as air flow thru the engine.
But the question is, what happens below this mark? The answer is: It depends on the type of motorcylce: The SD-"R" engine performs completely different compared to the "normal" 990ccm-LC8-engine used in the standard SD (without "R") or in the 990 SM..

in the case of a real "R" ( model after 2008) the larger 52mm intake track let this engine respond to the RC8-stacks straight forward: Just install them, dial the fuel in and you may aspects some real nice gain:





The base run shows a SD-R with an "open" airbox on it, of course - an old buddy of mine - pretty well "jetted", 2nd plates installed, velocity stacks stock. The other graph displays, what happens, if you remove the secondaries AND install said RC8-stacks. All runs done same day, same dyno. Could a dyno session be more effective?
No losses below 7000 and from this mark upwards the fire is burning. For those, who are able to read German take a lokk into the ktmforum.eu. Here this guy talks about is riding experience during a 1000km-trip thru the alps. He feels in the "real world" what this graphs are promising.

So in the case of a "real R"-SD that simple RC8-veloctiy-stack-swap works. But for the "normal" SD and 990-SM things are different: Here it depends on the actual "condition" of the bike, if that swap has the same effect as it hase in the case of the SD-R. This is a question of "production tolerances", of the indiviual cam timing, operating the LC8 engine.
So KTMjunkie´s bike has a reasonable mileage. Over the time the cam chain becomes longer and loner during wear, dialing effictive cam timing to the "late"-direction.
The most important factor for the position of peak torque within the rev range is the figure of "intake close". As longer as the intake is kept open, as more the engine becomes a "screamer", showing its best at the end of the power band for the price of performance at the buttom.
According that "screamer feature" at this bike the simple swap of the RC8-stacks created an huge gain in the upper part of the rev range but for the price of a noticeable loss below. So I am confident, the "seat of the pants"-impression of KTMjunkie, if he had ridden his bike in this condition, would have been like this: "Great power at the top, but no acceleration out of corners".
A "lucky bike", where the "individual circumstances" match better to the RC8-stack-effect, otherwise has a good chance, ro respond in a "on-R" SD manner, performing without any losses with this shorter stacks. But this is fortune.

That is a result which does not satisfy me. If I am creating a tuning package for a bike, it should perform no matter of "production tolerances" It should simply work for every 990. But there is a "work around" for this problem:

This mod couples the volume of the lower air box half to the volume above around the velocity stacks formed by the K&N-filter element:


Due of the iron net as part of its construction a K&N Filter reflects sound waves, not totally, but partially. Therefore such an element is able to define a wall, penetrable for air, which nevertheless makes a working resonance chamber around the velocity stacks.
By adding the volume of the lower stock air box half to volume inside of the K&N-filter, , the over all resonance of the system of air box AND intake path becomes different in a manner, it now matches nicely to the standard-LC8-engine. no matter of its internal tolerances.
To achieve the best effect, this volume should be really "closed":


(This is a R&D-pic. In the final commercial edition this hole will be plugged in a professional manner)

This is the "trick" which gives KTMjunkie´s bike back its torque at the bottum. And this "trick" simply works. I have tested this mod on several bikes, SDs and SMs, until today:

]



This dyno run of a "non-R" SD has been done yesterday. The base run shows the performance of a "ventilated" stock air box with snorchel removed und same air thru the triangle inspection lids. Additionally 2nd. plates removed, velocity stacks stock. Fueling was a shade on the lean side, but not dramatically.
The other graph shows the effect of RC8 stacks inside of "RESO - air box" as described with K&N filter at the top around the stacks and sais volume of the lower air box half joined to it.
Note: Nice power above 7000 with a shift of peak torque for serveral hundred rpms "upwards", but around 5250 the torque figure is unchanged (when talking about engine performance we should not talk about HP-numbers, but about the shape of the torquw-graph: This is the power which puls really). I guess this is a nice prove for the working of "RESO-air box"

I am aware this are no good news for the Motohooligan-fans around you (except SD-R-owners), looks like s there is some redisign necessary to make the RC8-stacks working for "non-R" SDs.
Highscore

Note: All dyno runs same day, same bike, same operator

Please excuse my grammar and spelling since Im no native speaker

Great work Highscore, it was mentioned 2 weeks ago on the SMT forum about your new air box design, please keep us posted on your developments.

Testing with James design DVS + RC8 stacks we have not lost any torque in the low to mid ranges & the results have been Dyno tested on two different bikes here in Oz, hopefully adding your new design air box we will see more gains.

Nice, clear and concise work, I have been trying to work out how to use the bottom airbox section volume together with an open filter myself,

Did you run the new filter design with the secondaries still in and the standard SD stacks

Cheers Russ.

High score have you done a back to back test with your filter & lid, with & without the lower box? This would show the gain from the lower air box mod.

Just what I'm looking for - viewtopic.php?f=5&t=19088&p=225799#p225799

Have tried already - Chris at CPR was quick to respond but was unwilling/unable to supply a 'non-standard' base plate or an oversized blank sheet that I could cut to suit - so definitely interested in one of Highscore's when available.

I will test this new version lower air box mod for interest sake using a DNA main filter + stage 2 & 3 lids to see the gains on my bike between the lids & lower box, I have the wheels in motion already.. I am not interested in comusally produing any air box it is High scores mod, buy I am always interested in new ideas & am willing to spend any amount of money to try make new mods & test them for self gains.

Well done to High score for bringing the idea to us.

Ps, I am looking a a old used standard OEM air filter if anyone has one they want to throw out.

Base run: RC8-stacks w/o 2nd-plates, solid air box ground plate, the other run shows shows the effect of the RESO-box by coupling the lower half of the stock air box to the system.

This runs have been recorded on KTMjunkie´s bike. This is extreme regarding its tolerances, because it is a real screamer. So here the RESO-box effect is very huge, other bikes react similar but not to this extend.
The torque graph - that is the one and only graph to analyze an engine characteristic - displays the resonance effect clearly: The new resonance scheme shifts the torque for aprox 200-250 rpm "upwards".

Strange thing, how could this help to boost performance in the lower part of the range? When changing intake path length by making the velocity stacks shorter or longer, things are not so straight forward as school books talk about them. Not necessarily a shorter intake length only "works" within the high-rpm-region: If this new and shorter length causes also a change, a transition within the harmonic order of the intake resonance, say from 4th to 5th order, such a - first hand - curious effect may happen: suddenly the engine starts pulling in the early part of its rev range.
The wave action at a higher harmonic order has the disadvantage of lower energy, so may be it does not create the same peak torque as running with longer stacks at a lower order. But such a "high order" set up has the clear advantage, that its Ram-effect occurs more often within the engine´s working range. Some of this high-order-ram-peaks also may happen within the first part of the power band. If that new Intake-peaks match "nicely", even real short stacks are able to make good torque at the bottom.

I am aware this sounds strange because it violates "common thinking". But such a shift to a higher harmonic order, by installing the short RC8-stacks, gives an explanation, why this mod works ONLY with removed secondaries: The wave pattern inside of the intake runners now has less energy, therefore it react more sensible to parasitic losses as created by the surface of the 2.nd. plates.
In the case of the LC8 throttle bodies, the bell of the velocity stacks does not start within the black plastic trumpet, indeed its "mouth" begins next to the primary butterfly, operated by the throttle grip. The secondary plates are therefore located exactly inside of the "atmospheric" end of the intake path, where the waves are being reflected.

In this respect the design of the LC8 TB is somehow unique. And it is a further, pure geometrical, problem of this design that is impossible to shorten the intake more as by installing said RC8-stacks onto this body.
The "Reso-box"-effect now seems to be able to do this job: The harmonics of this air box are joining with the harmonics inside the intake runners, creating a new and summary resonance pattern. The wave action now perform like that of real short intake path.

In case of the "normal" SD/SM-990-engine this summary resonance matches real efficiently to the engine, making real good peak torque with nice grunt from 3000 upwards.
In the case of the "R"-SD with 52mm TB this sharpening effect is too much. The RESO-box also works here, shifting the overall power band 200-250 rpm "upwards", performing like stacks, aprox 20mm shorter. The "R"-engine now becomes the ultimate screamer making peak power at the very end of its range, but peak torque suffers substantially. In the middle of the range the intake-RAM simply does not match:



This graph shows, what happens to a SD-R, equipped with RC8-stacks w/o secondaries, when the lower air box volume is coupled to the harmonic system of intake AND air box resonances: Simply does not work.

Resonances and interaction of resonances, building a single, a unique "vibrating" system: Here starts the "black art" of Intake-engineering with effects, hard (impossible?) to calculate. But obviously the effects a real and can be measured.

Just one thing:

O.k. my air box is really flat and it is simple. It is also simple to manufacture, so its price is - I guess - real reasonable: € 200,--. This is the price within Europe free to your door including 20% sales tax.

I have developed this box with the long stock SD-trumpets. I know the "rule of thumb" for the distance of the intake bell to an opposite wall too: should be trumpet diameter. And of course my air box violates this rule be far. Therefore, before starting the production of this box in 2009 - meanwhile there are here hundreds of units around the "old world" - it was a crucial question for me: Does this air box sacrifice engine performance?
The reference for this question was a test with real free breathing intake trumpets: no air box, no filter at all, just pure " atmosphere" for the engine to get its charge.

In simple words: One test run with my flat air box installed, one test run with open stacks on the dyno. The result: no difference in performance. I have repeated this test several times on different bikes. Always the same result.

So please tell me, what a higher air box can do better?

The real strange and curious thing with the new "RESO-box" is, that this design now is able, to make more power than free breathing stacks. This is something like a real wonder. But "well sorted" harmonics are able to to this job (sadly only in the case of 48mm TBs).