Larger airbox for big motors....fact or fiction?

[Busa Quick]

 I am sure you are better at engine building than I will probably ever be but, I still disagree on some word terms.
 
As defined by Google...  Vacuum is a pressure lower than atmospheric.


 No vacuum means no air movement period. If the piston is not moving and the valve is open you will have no vacuum. Vacuum is created by the piston moving down the cylinder and creating an empty void.

[whtrthanu]

Im just tryin to shed alittle light on the subject, thats all.....its easy to see your point of view, as would others, but think about what im trying to explain. If you put a vacuum guage on a running engine you will have a vacuum at idle, but what happens when you open the throttle, the vacuum goes away...........i went through this same thing many years ago......
I understand where your coming from on this...........

[Busa Quick]

   It all good. It is hard to describe something that we can't see or touch. All we have left is theory and experience.


 Mark

[DarkFalcon]

This thing gets interesting as the airbox is in the middle of two resonating spring mass systems: one between the intake snorkels and the airbox and the other between the airbox, throttle bodies and runners and cylinders. The first effect, which appears to be very sensitive to airbox volume, appears to occur at lower RPM's while the second effect appears to occur around the RPM of peak torque. Between the two, the latter is more useful and important as an engine design tool.

[Steve S]

The “humming” that drives the oscillation is the rapid succession of suction pulses at the carb or throttle-body intakes. If the volume of the airbox and the dimensions of the intake pipe(s) are correctly chosen, the airbox can be made to resonate very strongly, in step with the engine's suction pulses.

Steve, where did you find this info???
Im curious because an engine does not suck air in, there is a negative pressure inside the cylinder, atmospheric pressure outside the engine is higher so it is pushed into the motor........
i think you should research alittle more about this before jumping into it, I do believe you will see an increase in performance from a larger air box, but not much.  From my data I can tell you that an airbox should be no smaller than 10x the volume of 1 cylinder displacement. There are other factors that need to be considered also, but it is a good baseline to start.
1397 would be 21.3 ci X 10, so it would have to be no smaller than 213 ci... THe stock air box is bigger than this already, so i think your gains will be minimal at best

That particular quote uses the term "engine suction" pulses.............which is nothing more than shorthand for describing the vacuum created by the descent of the piston.

There are a number of formulas for calculating airbox volume but they should be viewed as nothing more than guidelines as resolution requires 3D computational fluid dynamics. In addition to volume, emphasis in the literature is given to shape, surface area and temperature.

In the case of the Busa, some of early studies of the effects of ram air indicate a partial vacuum in the airbox during the first 1200' of WOT acceleration which would suggest the airbox is possibly undersized for a 1.3 liter configuration. Thus, I'm inclined to believe larger engines would tend to benefit from larger airbox volumes. How much is a ????????

Higher frequency tuning resonances are dependent upon the two primary models employed to describe this phenomenon; neither incorporate airbox volume as a primary variable.

[gazza414]

It sounds as though no one has done any back to backs either on a dyno or dragstrip or mile plus events to really know the step changes..especially with bigger capacity motors..maybe Kent Riches can say whether the airbox and snorkels were a result of exhaustive R&D both on the screen and on the track / dyno OR for that matter just a good "gut" feel .

None the less its prob one of the areas still to be developed along with a better aero package for the Busa......all free HP in the scheme of things....I never really meant to say FREE

[Oz Booster]

In 93 i was working at a big race meet here in Aussie (Bathurst for the locals) and the Williams/renault teams had brought there car from the UK , 2 lit with (my est) 50 lit airboxes shaped very much like a 50 lit car type gas cylinder , intake rams were nearly central and a 4" square intake at the front, very interesting at the time, both the shape and volume used.

[Jonny Hotnuts]

maybe Kent Riches can say whether the airbox and snorkels were a result of exhaustive R&D both on the screen and on the track / dyno OR for that matter just a good "gut" feel .

From motobody:

Suzuki GSX 1300 Hayabusa Air box
If you' re racing a muscle, nitrous, or non-turbo Hayabusa you need this air box! Air box size is critical to throttle response and horsepower. After careful testing of prototypes, we settled on this incredible air box. This box has a slightly larger capacity than your stock air box, which allows your Busa to pull in more air on the bottom end, like drag racing launches where you need a lot of air when the bike is not moving to pressurizing the air box. This box was also designed with extensive testing at Bonneville to give you the max pressure on the top end. The result? Awesome! Get one and see for yourself!

Have you ever looked on the inside of your Hayabusa air box? Pretty gross isn' t it? The air has to make a lot of turns and changes many directions, it even has to go around the filter until it finally makes it into the throttle body. This air box solves all of those problems and gives your motor a direct “ram” effect right into the stacks. This box comes with our high flow air ducts. Our air duct assembly slides through the frame and into the air box, which helps avoid any air bleed off at the connection joining surfaces. This is a serious air box, for serious racers!

[DarkFalcon]

Interesting Oz. In one of the papers mentioned by Y2K, mention is made of a "typical" 50 liter Formula 1 airbox ......and the typical displacement for one of these engines in 06 and later is 2.4 liters, making the volume of the airbox 21 times larger than the engine. Airbox volume compared to the volume of one cylinder is insane.

[Oz Booster]

Bikes seem to be  more what fits than what works best !

Anyone used a yosh style airbox base that has the tank as the airbox top???

[PetriK]

Has anyone tested the optimum runner lenght for busa which is 3.181 for 1397 from manifold to the opening of velocity stack ? (Difficult, I know its requires cutting the TB) Also the taper would then require a some change ...

Just wondering if using any kind of airbox changes the intake tuning lenghts ?

[PetriK]

Did some more investigation of this topic ... without fully understanding the dynamics behind the induction theory beyond normal primary intake manifolds all I could do was modelling with EAP. With that I could see the following:
- Adding the large volume airbox (using busa original airbox size) adds 5% to the power output (VE) compared to individual runners without airbox.
- Adding airbox volume adds hp even to a 1299 engine
- Adding airbox duct length adds hp to a certain point
Anyhow EAP does not give exactly the design method that busa is using so this may not be so straight forward.

On the other hand with 1397 the induction tuning of primary manifold length to the exact lenght (throttle bodies and stacks measured to closest harmonic) gave appr 5-6hp more in EAP which I expect to be very realistic also in real life. Adding TB from 46mm to 48mm diameter did not really yield anything.

The exhausts seem to be very close to optimum already today when using pipemax or other tuning packages to analyze the lengths of sections and compare those to harmonics. Instead finetuning the whole induction path is propably the area where there could be more to be gained for non stock cc engines ? The current busa airbox ducts do look more like pipes where main design prinsiple has been noise reduction rather than flow optimization, but e.g. things like the englargement in the beginning can be considered as a secondary airbox. Need to check the harmonics and sizes.

So it soulds like time to do some practical testing around this topic when the bike is in dyno. All we know for sure is that leaving the airbox out of the equation reduces the power output significantly - that we tested in a dyno for some time ago.

EDIT, adding some interesting links here:
http://www.saltmine.org.uk/randy/airboxdesign.html
http://www.ducati.ms/forums/showthread.php?t=18854
http://upetd.up.ac.za/thesis/available/etd-01242006-123639/unrestricted/00dissertation.pdf

EDIT2, some measurements about Busa Hemholz box
Anyone modelling the busa engine in EAP, the airbox size is about 550cu in of which the area below lid is about 122cu in, the 2 entry holes are about 3.15"*1.77" . Could not take exact measurements of the box because it started leaking in the middle of the process.

[396]

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[DarkFalcon]

PetriK, a nice effort on your part.

Before reading your edited post providing a link to the Pretoria dissertation, I stumbled upon it while looking around. Anyway, it is there for all to read but I found a number of itmes to be of particular interest, including non-linear wave activity and the concept of diffusion as applied to airboxes.

As air moves from the point of entry towards the stacks, the Busa airbox widens; as air moves from the roof of the box towards the stacks, the airbox widens. The importance of reducing velocity as air approaches the stacks has not been lost on Suzuki engineers.

[gazza414]

DF, I managed to get thru 1/2 of the paper mentioned last night..there are no doubt some good insights. There is alot of modelling which is debatable how one can relate this  to individuals applications and then verify if we have gone "forward" or backwards?..on the R6 there were close correlations granted.

The issue of geometry still stands out as a show stopper when modeling the entire package.

......none the less I havent seen  or heard to many builders concerning themselves with this area...dunno why?

[PetriK]

......none the less I havent seen  or heard to many builders concerning themselves with this area...dunno why?

This is not an easy area to understand - its not one of the familiar concepts: its not the volume, its not the flow rate. Its about pulse wave tuning which requires optimizing the airbox design for a certain resonance ?

I just spent some time by looking a naked ZZR1400 frame which has an integrated airbox - which could well be one of the areas for improvement. The bellmouths are way too close to each other, if you take the air filter out the box shape is not optimum either - not working at all. Anyway it looks like kawi has been thinking of possible wave tuning methods by having some space towards the back of the box allowing more volume to be added if needed .... Particularly the backpressure pulse dividers on top of the cylinders told that something has gone wrong during the design phase ? (Maybe a reflection from a hard metal surface overrides the Hemholz pulses)

Regarding Busa intake optimization for 1397 I am thinking of the following path:
- Reduce the intake lenght to closer to 4.1", possibly to 4.5" for a flatter curve on top. I am thinking of cutting off total of 0.35"  from both ends of TB:s and possibly from head too. This part of the excesise worries me as, but dont really see an option without changing the taper. Alternatively shorter TBs could do the trick but that involves then rebuilding the full cabling, injector feeds etc.
- Increase the airbox volume by dropping the bellmouth area by 0.5-1" (a bit more than the intakes are coming down). That should add a couple of liters of volume more to the back end of the box and retain the original shape.

If the calculations and modelling are right we are talking about 5-10hp here between 8 - 11.500rpm (based on EAP estimations) if the above is doable and assumptions are correct. By doing the simulations I have already verified that the current intake lenght 4.85" is exactly the optimum length for stock busa - so that is a very good starting point to know that the intake lenght calculations are most likely correct.

Question1: Any suggestions of how the cutting may affect the TBs as I have no way what I am about to cut into when making the round area of the TBs and possibly in the head about 0.1-0.2" deeper...

Question2: Remeasured the airbox size and it seems to be 550cu in + 122 cu in, do you guys see if the airfilter somehow splits the volume or not ? My guess is that it does not necessarily affect the volume as the lid is on the other side of the resonator. Which gives an option to increase the volume on the dirty air side of the filter.

[gazza414]

One option Petri would be to consider what Richard @RCC put forward on this board some months ago wrt the new style T/B's that dont incorporate butterflies...these to my mind offer a few advantages that may or may not address your design concept....potentially shorter overall length, could be made to suit your taoer rquirements, could have an integral bell mouth ( stack) to your design....... they would offer potentially more flow based on same ID due to no butterfly and supporting shaft.

something to think about

[PetriK]

Dont know if this is already now getting OT - but, all the material I have read says that its more important first to redesign the manifold lenght and only after that to look into the airbox size. All shorts is too long for 1397cc and even more too long for 1500cc engine... shortening the intake, but maintaining the belmouth shape and distance from the bottom of the airbox seems to be the way to go. E.g. Gordon P Blair has published a very good article about the belmouth design and looks like busa already has the best design available inside the box. http://www.profblairandassociates.com/pdfs/RET_Bellmouth_Sept.pdf

One option Petri would be to consider what Richard @RCC put forward on this board some months ago wrt the new style T/B's that dont incorporate butterflies...these to my mind offer a few advantages that may or may not address your design concept....potentially shorter overall length, could be made to suit your taoer rquirements, could have an integral bell mouth ( stack) to your design....... they would offer potentially more flow based on same ID due to no butterfly and supporting shaft.

something to think about

Thanks Gazza - certainly an option to change the TBs has come into my mind. Anyhow that would mean changing one of the design prinsiples: "I am trying to modify engine, not redesign. Modifying means things that everyone can replicate easily.". Hacking the ecu was step1 to have better tuning possibilities than before. Now the engine parameters are fixed and even the chosen exhaust seems to be exactly optimum from wave tuning perspective for 1397cc. The only area not yet completed is the intake design including two parameters:
- Airbox size
- Intake manifold length

Yesterday I precut some spare stacks and found out that just by cutting some rubber should allow me for appr 1cm (0.4") shortening without major modifications to TBs. Then today came to a conclusion that using a cup drill (??) which has internal diameter of appr 51mm and cutting about 0.5cm(0.2") off the manifold in head I can get very close to the optimum 4.1" manifold lenght. Btw. seems to be better to have just a bit longer manifold than too short so the actual target is 4.25" just to be on the safe side. I may try to do the drilling and cutting the head tonight to get the exact figures and to see if I hit any coolant passages

When the manifold lenght becomes fixed I can redesign the airbox just by cutting it into two pieces (lower back quarter vs top and front part) and dropping the lower back quarter the same amount as the intake manifold lenght is shortened.  Some glassfiber, plastic padding and sandpaper should do the trick of increasing the airbox size by a half of a liter (or even a bit more) which is about 6% more airbox volme for an engine that has 7.5% increase in displacement.

Btw the oil breather takes quite a lot of space inside the airbox. On the other hand any vacuum to crankcase will certainly add more power. So one option is to utilize pair or pair alike device that is open also at higher revs and remove the oil breather cover from airbox and free more space inside airbox. Anyhow I doubt that I will change that as I dont want to go to redesigning components - the plan is just to modify the intake to match the 1397cc engine. If anyone else has done anything alike I would be very interested to hear comments and feedback.

[glenn71]

Ive split my airbox removed the crankcase breather bulkhead,made another lid so all the screw bosses arent hanging down,raised the floor to the ram air ducts and made it a large airbox mod with a flat panel foam filter in place.I,ve always been told the motor only sees airbox volume on the engine side of an air filter.Just going to the large airbox mod dramatically increases the airbox volume on the engine side of the filter.Just have to do some like for like airfuel tuning then my accelerometer can tell me what my arse can,t.

[PetriK]

We did some experiments with a a damaged head yesterday night by drilling with a cup drill around the existing intake port inlet. The material there allows appr 0.60" shortening of the intake port. Based on this experiment we have now decided to cut the intake port 0.40" shorter from the head. The shortening of the port also seems to help in reshaping the port floor curve. There is additional 0.20" gain from the stacks by reshaping the area how the rubber is joined to the TB. This now allows the airbox bottom being dropped by 0.6" to increase the volume and simultaneously to match the intake wave resonation to the 1397cc engine with Brocks in031 intake cam@108w with 10500rpm peak power target. Come up to these figures by using the stock engine and intake lenght as a starting point and verifying the shortening of the intake manifold and port with the above parameters with three different calculation methods. Particularly the bsgoflex and wallace racing formulas gave numbers very close to the stock lengths and EAP supported these findings.

Anyway while doing research on this topic found out that there seems to be a wide variety of calculators in the internet. Unfortunately many of the calculators gave varying results. E.g. wallace racing calculates the following:

1397 with Brocks intake cam @ 108
(Own set target is 4.6”+4.65”=9.25”)
Engine Pro - Intake Port Length is 7 inches
Helmholtz Formula - Intake Length is 5.49 inches
Gordon Blair Formula - Intake Length is 5.20 inches
Simplified Chryser Formula - Intake Length is 7.64 inches
Simplified Chryser Formula (with bigger cam) - Intake Length is 7.30 inches
Simplified Formula - Intake Length is 7.20 inches
Simplified Formula 2 - Intake Length is 8.90 inches
Simplified Formula 3 - Intake Length is 8.40 inches

1298 Busa Stock engine
(Stock actual is 5”+4.85”=9.85”)
Engine Pro - Intake Port Length is 10 inches
Helmholtz Formula - Intake Length is 7.61 inches
Gordon Blair Formula - Intake Length is 4.98 inches
Simplified Chryser Formula - Intake Length is 8.84 inches
Simplified Chryser Formula (with bigger cam) - Intake Length is 8.45 inches
Simplified Formula - Intake Length is 8.34 inches
Simplified Formula 2 - Intake Length is 10.31 inches
Simplified Formula 3 - Intake Length is 9.73 inches

Some reference links for calculators and other interesting links:
http://www.bgsoflex.com/intakeln.html
http://www.wallaceracing.com/intake-runner-length.php
http://www.velocity-of-sound.com/velocity_of_sound/calculator3.htm
http://www.bid2race.com/calcs/
http://www.racejunk.com/tech.html
http://www.supramania.com/forums/showthread.php?t=68308

Completely OT - Do you guys in US always get cams painted ? It was so funny to use gasket remover for the cams to remove the paint around the lifter areas as the first installation step...

[DarkFalcon]

There are three different acoustical tuning models..............and the competing formulas are simply mathematical expressions of the different models; each yields its own induction design. And while there has been much debate and research, no model has been completely discarded.

[PetriK]

There are three different acoustical tuning models..............and the competing formulas are simply mathematical expressions of the different models; each yields its own induction design. And while there has been much debate and research, no model has been completely discarded.

Yes - so as the stock bike gives us some guidelines how Suzuki originally thought the induction to work propably based on a lot of testing. Therefore reverse engineering the existing stock bike to fit to any of the models gives a baseline to compare to  and then apply the changes recommended by various formulas. (Btw I believe there is more intake calculation formulas than wave tuning models as some of those are simplifying the models as such.)

But the key question is how do we choose which model to put into the practise here... ? Luckily all the models suggest the following...
1) When RPM increase the intake total lenght should be reduced and airbox size should be increased
2) When displacement increase the intake total lenght should be reduced and airbox size should be increased

So we can assume that what ever the case is the intake tract length should be shorter for a larger displacement. In average when displacement goes up from 80 to 85cid the intake manifold is recommended to be 0.48" shorter by various formulas. Additionally gordon blair and pretordia documents advice to have a minimum floor distance for the belmouth so the change of the lenght can not happen by shortening the runner length inside the airbox - so by changing the intake manifold lenght can only take place outside the airbox which then allows making the box larger.

                   1299cc   1397cc      Shorter

Hemholz            6.41   5.49     -0.92
Gordon Blair       5.45   5.2      -0.25
Simplified Chrysler 8     7.46     -0.54
Simpl. Chrysler 2  7.65   7.3      -0.35
Simpl formula      7.54   7.2      -0.34
Simpl formula 2    9.32   8.9      -0.42
Simpl formula 3    8.8    8.4      -0.4
EAP simulated      9.85   9.25     -0.6
Note - the figures here are different to the above posting as these only reflect the effect of the engine size change, not including peak rpm change which are introduced earlier.

As some of these formulas are based on actual intake closing point which generates the reverse wave and vary because of different cam profiles and possible desired rpm peak target so the actual figures may vary engine by engine (I assume).

Based on the above the -0.40" from the block sounds like a good starting point for the initial dyno and additional -0.20" after later dyno sessions will confirm if the direction is right.  Additionally as EAP from start gives the close to optimum curves for the stock engine intake length I believe it to give also very good starting point for this experiment of shortening the intake.

But as always - comments and real life experience would be interesting to know ... Has anyone tried this larger airbox from the beginning of the thread and what has been the result ?

[Steve S]

PetriK, you are co-mingling too many variables.

RPM is a variable in each of the three models; cam timing figures into two of the models; and displacement is only a variable in the Helmholtz model.

When displacement increase the intake total lenght should be reduced and airbox size should be increased

That conclusion is simply not true because (1) in two of the three models displacement is not a variable and (2) airbox volume is a function of, among other things, displacement times RPM.

Because of the uncertainties, I would be inclined to play around with various stack lengths before cutting metal. And, I would attempt to tune for a mid-point of a range which would give me latitude for error on either side of my target.

[PetriK]

Because of the uncertainties, I would be inclined to play around with various stack lengths before cutting metal. And, I would attempt to tune for a mid-point of a range which would give me latitude for error on either side of my target.

Without knowing the exact maths behind the models, are you saying that when the displacement goes up and the target rpm goes up there is still a potential scenario where the one or some of the models does not suggest reduction of manifold length or airbox size requirement does not increase ??? Please give an example for me to understand ! (Assuming that we are still targetting for the same harmonic resonance.)

[Steve S]

Neither organ pipe or water hammer are sensitive to displacement. The simplified Chryler formula developed by Billy Shope and based upon water hammer is shown below:

N x L = 84,000

N= RPM

L= length

12,000*7=84,000

Induction path would be 7" for 12,000 and the imbedded cam timing and would get shorter only as a function of RPM.