TZR Forum

Looking on the old forums, there are a lot of references, to the different airboxes. Some pics aren´t there anymore wich is a shame, but nevertheless references, are.

This is imo, quite an important issue specially on road going bikes, and for people as myself that don´t fully understand the meaning of an airbox, or better, the consequences of modifying a gearbox.

Common practice seems to be to "upgrade" the left hand cylinder lid to SP spec, and by this get rid of the possible airflow obstacle that the tapered intake tube has. But this got me thinking...
The right hand cylinder airbox also has a "restrictor" device inthe tube that connects the vertical tube to the airbox body... and this is, in most cases kept by the people modifying airboxes.
When there is air flow involved caused by different pressures involved, intake diameters, lenghts etc play a major role imo, and I´m a bit scared that just cutting away would really be to no usefull effect.
There is of course the side that the upper lid was modified for 1995, while the right hand cylinder airbox was not...

I stod ready with a heated knife blade ;D, ready to cut the snorkel on the upper lidt, but then I thought I´d better writte something here first, and hope for some opinions to show up.

Does someone remember if in the past someone tested upper lid "mod" vs standart?
Or some good opinions on this subject would be great.

Rui

ramair pod filters are supposed to be ok on all 3xv's, putting em on my r with martin 77 ported barrels n dfr chambers ,sugo plugs instead of boost bottles ,n all heating pipes removed from carbs,cheap too mine were £30 for a pair delivered ;)

Cut it...

Before:

(https://pure2strokespirit.net/forums/proxy.php?request=http%3A%2F%2Fi721.photobucket.com%2Falbums%2Fww216%2Fjcsnook%2FYamaha%2520TZR%2520250%2FIMG_2001.jpg&hash=307da12c97de631faf26e8ef4f0e3d44df3c8a97)

After:

(https://pure2strokespirit.net/forums/proxy.php?request=http%3A%2F%2Fi721.photobucket.com%2Falbums%2Fww216%2Fjcsnook%2FYamaha%2520TZR%2520250%2FIMG_2003.jpg&hash=4df4c0cbad241d687b4a56dd883a5d69802e6be0)

i cut mine and kept the bit ,but never try'd it ! ive gone to pod filters as well
£35 for a pair they look pretty good ! not used yet as its still in bits !
i will post something once its dyno'd

i've modded both the upper & lower airboxes on my 3XV,i'll post the pics soon as i find where i put them!!  :P

Hi Rui,
funny, I thought the same! If we want to stick with the air boxes (instead using the pods which I do eg. on my RZ and they work perfect) I think the mod for the upper box is clear. But I fully agree (if I understand your point correct  :D) the rubber hose or connection between the lower boxes will still restrict the air flow (assuming we run a 32 or even more worse than with the 36mm flat slides)! I still had a first look how to change that but still need some time as priorities are set different at the moment. Looking forward for other opinions, EEKNOWS  :D  ?
Juergen

excuse me for butting in here
what are you trying to achieve?
or is it legistrature that is influincing your decision
are you looking to open it up and roar around?
most race bikes use nothing behind the carbs
i use mesh on TZ and pods on MC21 (and 3XV - added later), mainly because im scared of sucking stones
my 3XV would only run without airboxes after derestricting motor, custom pipes, Ignitech CDI and sugo carbs
if you are eventually going to come to this point over time, dont cut your airboxes as you have a scanario where it'll run as standard and you can always go back there for MOT/COR/testing.
are you running the little 28's?
for me i always start at what the end goal must be and work backwards, then it is clear to me what i can cut, hack or sell or throw away
(i have SP and std boxes for sale in for-sale section by the way)
else you just end up playing with jetting and running more risk of seizing/damage with every small change you make

Thank you all for the feedback.
Paul, I totally agree with you about setting a goal, and define where you want to go before you start going.
For the rest, just trying to get some input on something not yet discussed before (?), the little rubber tube connecting the upright tube that feeds the right cylinder rearbox.

Juergen, me too looking forward to see how peole tackled this.

Kingy, looking forward to see the pics. Running 28mm carbs? Or did you try it with 28mm carbs?
By the way, congrats with the 2012 results.

Good pic jc, thanks.

When using the 28s, the only airbox mods I made was to use the freer flowing SP top airbox lid. It didn't look like the lower airbox link tube was quite as restrictive of flow, so I left that alone. It seemed to work pretty well. I ran the SP upper box lid from the off, but a friend was using an R upper lid on a very similar set-up to mine. Borrowing the SP top box lid gave him about 1bhp at the top end in back to back testing so he bought one. I made some other changes to the carburation (needles and nozzles) after initial set-up with the 28s and it seemed to give some improvements to the power feel over the initial set-up, but I never got round to dynoing it again like that as I went over to the bigger carbs before I had the chance to get back on the rig.

Might be best to get a base reading with the boxes completely stock and then try mods though so that you can properly assess their effectiveness?  The 28s seem quite sensitive to airbox mods though, so you may have to jet any mods in a bit to get it working well after after any airbox mods ???.

Quote from: 41juergen on January 20, 2013, 12:23:58 PM
Looking forward for other opinions, EEKNOWS  :D  ?
Juergen

Sure thing here is what happened when we removed the 'restrictive' snorkel from a Aprilia RS 125

(https://pure2strokespirit.net/forums/proxy.php?request=http%3A%2F%2Fi155.photobucket.com%2Falbums%2Fs297%2FLozza85_2007%2Fsnorkelvsnosnorkel.jpg&hash=e8a6a2050c5508641a5072fe6ee815dd97f16313)

Quote from: Warwick on January 21, 2013, 12:25:30 AM
...you may have to jet any mods in a bit to get it working well after after any airbox mods ???.

was rejetted got 2HP lost back but using more fuel. Juice not worth the squeeze on that one.

So it was worse ?

I don't want to start an argument , but will the 3xv behave the same way if the airboxes are changed / modified etc ?

Probably not that much of a comparison, but still a fairly highly strung 2T, albeit a single........My Cagiva Mito 125's run rubbish in the mid range when the snorkels are removed or when running a pod filter, (even with re-jetting) they also usually drop a couple of peak hp from graphs I have seen (which is quite alot as they are not that powerfull anyway.lol circa 32-34 quoted  in the manuals depending on model). I always run airbox's with the correct snorkel type on mine & they run perfect.(there are 3 fpwr types depending on spec).  I see it as Cagiva new what they were doing with the airbox & snorkel design  ;)

Hi guys,

I'll give my take on the airboxes.

I'm running the right hand box as stock for a 92 RS model with SPR airbox to carb rubbers.

I'm running the left hand box with an early SP airbox lid and SPR airbox to carb rubbers.

Early SP 36mm carbs.

I've had fairly good results with the airboxes as above. The intake to the upper airbox is larger compared to the one for the lower cylinder. I'm having to run 3 jet sizes larger on the left hand side compared to the right cylinder and even then the right cylinder is running richer than the left.

It is unclear as yet whether the airboxes are what is causing my bike to drop off so sharply after peak but that will be investigated next time I get it on the dyno.

One test we did do last time was to remove the air filter element from the right hand box and compare that to a run with the air filter element fitted. The gas analyser showed that the mixture went leaner with the filter removed compared to when it was fitted. That tells me that the snorkel on the airbox WAS NOT governing the airflow into the right hand cylinder. If it was, the mixture wouldn't have changed. Yes I know people say the gas analysers are not accurate, I probably agree, however it was the relative change in gas analyser reading that was interesting. It went from 12.5:1 to 13.5:1 which is a big change.

I'm sticking with the airboxes until they become the limiting factor, as yet I don't think I have reached that point.

Dan

With the 38s I need to run some holes in both airbox lids (SP upper) if running the airboxes. As noted above though, the only sensible way to approach this stuff is to empirically test things as you go, so, as mentioned previously:  it is probably '...best to get a base reading with the boxes completely stock and then try mods... so that you can properly assess their effectiveness?' On the specific bike in question...

Have you tried some holes in the lids, Dan? I know your carbs are slightly smaller, but with the 38s mine is significantly choked if running unmodded boxes I have to say. I use extremely free flowing 'filters'. I don't think I'll be running the oe airboxes at all on the track 3XV this year myself though in fact. More clutter gone. Nice! Just got to stop the carbs eating things...

Not yet Warwick, I'll see how we get on next time on the dyno. It might be what's needed to get it revving, however I will investigate all other avenues to see if something else is holding the game up first  8)

Dan

Yup. I love the smell of systematic testing in the morning... 8)

my airbox pics as promised,i'm running martin 77 pipes and (almost) sp spec ported r cylinders,stock 28mm carbs,rejetted to 220 upper & 270 lower,making good power ( last dynojet run was JUST under 60 bhp on the stock cdi) revs like a good 'un, no flat spots or anything  ;D

Ian,

Was all that modding "necessary" to get your bike to rev or run properly?  Just curious mind you, not critical, as I don't think Warwick went that far with his airbox mods and obtained similar HP output with stock 28mm carbs.

To each his own state of tune I suppose.  I'll be doing my own experimenting soon I guess once I get my SP spec ported barrels back from having the o-ring grooves cut in them, and get the one original piston back from Wossner 8)

prob not totally necessary TBH,just my own take on trying to get as much air into the airboxes as poss really.
lower box does look like it's designed for a bigger intake though don't you think? hence my mod.... ;D

Is it not just a whole lot easier to run a set of pod filters with 38's, or am I missing something here??

When first developing it it was a road bike so I preferred to retain the airboxes on balance. There can also be issues with clearance and the position of the filter on the lower cyl of course.

There is a tech artical by Kevin Cameron

The airbox used to be just an intake silencer and a place to put the air filter. Now it's much more than that, so read on before you gut or toss your box. Just as is being done on new cars and motorcycles airboxes and their intakes are being built as resonant systems. When the airbox is resonating strongly, driven by the engine's suction pulses, its rapid internal pressure fluctuation covers a range of plus and minus 10-15%. This is just like the resonance of a bottle when you hum into it. If your engine's intake events run in step with the positive side of this resonance, it's just like getting a 10-15% supercharge boost for free. That's worth having. And what if you modify your engine, raising its peak-power rpm beyond the range of the airbox resonant frequency? There is a simple relationship you can use to alter airbox frequency by changing the length and/or diameter of the airbox intake pipe(s). That's worth having.

Any hi-fi enthusiast knows that woofer enclosures work best when the resonant frequency of the enclosure is nicely centered on the speaker's response range. The enclosure usually consists of a sealed volume with the speaker installed in one of its walls, and an opening, called a reflex port, cut into the enclosure. A resonant system consists of a mass, which vibrates back and forth against the restraint of something flexible, like a spring, with an excitatory force to drive it. In the case of the speaker enclosure, the mass is the air in and within one diameter's distance of the reflex port. The spring is the compressible air inside the enclosure. The system is set into vibration by the amplifier, driving the speaker cone back and forth as a piston.

In the case of an engine's intake airbox, the mass is the air in the airbox inlet pipe(s). The "spring" is the compressibility of the air in the box. The excitatory force - a very powerful one - is the endless sequence of strong engine intake suction pulses from the carburetors. The airbox must not have any significant leaks, as the throttled, back-and-forth airflow through them acts like a hand on a vibrating bell (anyone who's ever tried to play low notes on a valved wind instrument knows what a killer leakage is). The airbox inlet pipe is usually made with a smooth bellmouth on either end to reduce flow losses. Carburetors or throttle bodies must likewise seal positively to the box. When a system like this gets to humming, the pressure inside it vibrates rapidly plus and minus 10-15% of atmospheric pressure. In fact, the humming is so powerful that in many cases a sub-resonator is placed near the atmosphere end of the inlet, to prevent radiation of this powerful honking sound to the outside. EPA objectors are always waiting there with calibrated sound meters and spectrum analyzers at the ready.

How can you adjust the resonant frequency of your airbox if you raise your engine's peak-torque rpm with pipes or porting? One way is to invest $30,000 or so in professional wave dynamics software like Ricardo "Wave", running on a $10,000 Sun workstation. Probably on the right back street in Hong Kong you can pick up a pirate copy for $25, but which street is it?



We're so used to the idea that problems have to be solved with silicon logic that we forget about steel and aluminum solutions. "Wave" is great if you have a tricky fuel mixture glitch with #7 cylinder in your Ford NASCAR engine. But with a simple formula that tells us which variables push the airbox frequency which way, and by approximately how much, we can devise dyno experiments that will get us the answers we need - without those expensive Cathay-Pacific coach tickets.

Here is the formula.
(Airbox Frequency), squared, is proportional to inlet pipe area/(airbox volume X inlet length)

This is useful because it shows us that if we want to raise airbox resonant frequency, we must increase inlet pipe area or decrease airbox volume or inlet pipe length.

AN EXAMPLE

If our present engine is a twin, giving peak torque at 8200 rpm, that is 8200/60 = 137 revolutions per second, or 137 X 2 = 273 suction pulses per second. Unless there is some special problem, the airbox will be designed to resonate near that frequency.

If we now want to raise peak torque revs by 10%, to 9020 rpm, we must also raise airbox frequency by a similar amount. If we raise airbox frequency by 10%, its square will increase by 1.1 X 1.1 = 1.21 times, or 21%. That means that whatever is on the right-hand side of the equation must also increase by a factor of 1.21. Take your pick.

You can:
(a) increase inlet pipe area 21% (that is, increase its diameter by 10%) or,
(b) decrease airbox volume by 21% or,
(c) decrease inlet pipe length by 21%

Because these systems generally work better the bigger you make the airbox, we won't try (b). Since we are raising revs and power, increasing inlet area looks pretty good, so we could choose option (a), increasing inlet pipe area. However, option (c) would appear to be the easiest. Before we go to the dyno, we'll make up a few airbox inlet pipes to give us some test choices. Then we can run through our tests quickly and zero in on the sweet spot. Each end of the box inlet pipe should have a smooth bellmouth.

Likewise, go carefully before removing internal airbox "furniture". Assume nothing, but test with each change to understand its effect. Airbox designs are sophisticated now, so their internal features often have functions.

Any resonant system always has anti-resonances. In the case of an airbox, that is an rpm at which the engine breathes from the box when pressure is at the low part of its cycle. What if there's an anti-resonance right where you want your clutch to engage? Of course you could imagine a system with a variable-length inlet pipe to deal with this, but the easy way is just to kill the anti-resonance by opening a big hole in the airbox. Systems of this type are in use on certain sports motorcycles. When the engine runs near the rpm of the anti-resonance, the engine control computer tells a little motor to open the airbox port. When it revs up, the motor closes the port.

Isn't life getting complicated?

Just to stirr up this thread:   ;D

(https://sphotos-b.xx.fbcdn.net/hphotos-ash4/484859_461081967280123_630976411_n.jpg)

Eagle-eyed viewers will note that the lid on the far left is an SP lid. Useful to be able to see the SP intake trumpet like that.

Also of possible interest for those who like to ponder such things is the little 'boost bottle' that is oe fitment on the SP models' square lower cyl airbox intake pipe... Some kind of aid to bottom-end carburation I imagine?

Quote from: Warwick on January 24, 2013, 12:31:35 AM
Eagle-eyed viewers will note that the lid on the far left is an SP lid. Useful to be able to see the SP intake trumpet like that.

Also of possible interest for those who like to ponder such things is the little 'boost bottle' that is oe fitment on the SP models' square lower cyl airbox intake pipe... Some kind of aid to bottom-end carburation I imagine?

I never noticed that "boost bottle" added to the lower cylinder airbox intake pipe!  ???  Interesting...

Quote from: Warwick on January 24, 2013, 12:31:35 AM
Eagle-eyed viewers will note that the lid on the far left is an SP lid. Useful to be able to see the SP intake trumpet like that.

Also of possible interest for those who like to ponder such things is the little 'boost bottle' that is oe fitment on the SP models' square lower cyl airbox intake pipe... Some kind of aid to bottom-end carburation I imagine?

It can also be used to heat up the intake air as you can see this done on cars intakes.
(https://pure2strokespirit.net/forums/proxy.php?request=http%3A%2F%2Fi.ebayimg.com%2Ft%2F07-08-09-10-CADILLAC-ESCALADE-YUKON-TAHOE-SILVERADO-SIERRA-AIR-BOX-FILTER-HOSE-%2F00%2Fs%2FNzgwWDk0NQ%3D%3D%2F%24%28KGrHqJ%2C%21hQFC7g9QEKjBQ%2B4KNvdJQ%7E%7E60_58.JPG&hash=b2a41a1888cf91b31e018640e6960661e85c27a9)

I also only recently noticed the little extra bottle on the lower airbox on my SPR. Never really understood what it was for, cant imagine that it makes a big difference ?:-|

Quote from: Neal on January 22, 2013, 10:08:45 AM
So it was worse ?

I don't want to start an argument , but will the 3xv behave the same way if the airboxes are changed / modified etc ?

was a lot of work to get back to where it was with the airbox snorkel fitted, sounded great but noise doesn't equal HP. So snorkel went back in and jets size went down. Ever since then I have run engines with an airbox. I'm not overly sure of the method of tuning a airbox to the engine but bigger seems to be better, smaller airboxes seem to be sensitive to changes. Only way to check is on  a drag strip or dyno.

Mbsteve - while I appreciate you pointing out the highly technical theory behind airboxes being developed today, in your opinion, how much of that was known and incorporated into the design of lets say a 3XV1 22 years ago?

Hi Crank - I was there 22 years ago and this was normal thinking in racing and factories - I normally explains this way:
Take a garden hose open the wather pipe to your decided pressaure - find the were the water comes out - squice with your finger so that the opening are reduced and the pressaure increase - if you squice to mutch the length of the water are shorter, if you open too much - the length af the water are shorter - the maximum performance are were the opening produce the most presaure without limiting the quantity of water passing... think this metaphor - when you are looking at the intake "snorkels" in any form and shape that they appear - then think "green garden water hose"  ;) ..consider this in all aspects in you engine - not all tuning are done by making things bigger - it appears that smaller venturies incrase performance too ..

Quote from: Need4speed on January 24, 2013, 10:49:17 AM
Hi Crank - I was there 22 years ago and this was normal thinking in racing and factories - I normally explains this way:
Take a garden hose open the wather pipe to your decided pressaure - find the were the water comes out - squice with your finger so that the opening are reduced and the pressaure increase - if you squice to mutch the length of the water are shorter, if you open too much - the length af the water are shorter - the maximum performance are were the opening produce the most presaure without limiting the quantity of water passing... think this metaphor - when you are looking at the intake "snorkels" in any form and shape that they appear - then think "green garden water hose"  ;) ..consider this in all aspects in you engine - not all tuning are done by making things bigger - it appears that smaller venturies incrase performance too ..

That's not only with airboxes.

Quote from: Need4speed on January 24, 2013, 10:49:17 AM
Hi Crank - I was there 22 years ago and this was normal thinking in racing and factories - I normally explains this way:
Take a garden hose open the wather pipe to your decided pressaure - find the were the water comes out - squice with your finger so that the opening are reduced and the pressaure increase - if you squice to mutch the length of the water are shorter, if you open too much - the length af the water are shorter - the maximum performance are were the opening produce the most presaure without limiting the quantity of water passing... think this metaphor - when you are looking at the intake "snorkels" in any form and shape that they appear - then think "green garden water hose"  ;) ..consider this in all aspects in you engine - not all tuning are done by making things bigger - it appears that smaller venturies incrase performance too ..

Hey Need4speed when you say open the tap to a desired pressure, my question to you is...
1.where is the pressure measured at in the pipe?
2.when you close the hose the pressure before your finger will increase and the " velocity" of the water exiting after you finger will increase.
3. the theory behind this is all to do with "air speed" and cylinder filling, thats why a smaller venturi will increase "torque" and rob HP high up in the rev range to a given point where you will need to "increase" the venturi to gain HP. lost by a small venturi.

So thus the theory of"go big or go home" doesnt always work in all applications.
If you gain both torque and hp throughout your rev range it means the venturi was to small in the first place.

Have you guys seen the "trumpets" that fit onto open carbs ? They are supposed to help with improving the velocity of the incoming air . The same principle if you have a 2L bottle of water - when you swirl it around and flip it upside down the water exits much faster .

Quote from: Warwick on January 24, 2013, 12:31:35 AM
Eagle-eyed viewers will note that the lid on the far left is an SP lid. Useful to be able to see the SP intake trumpet like that.

Also of possible interest for those who like to ponder such things is the little 'boost bottle' that is oe fitment on the SP models' square lower cyl airbox intake pipe... Some kind of aid to bottom-end carburation I imagine?

(https://pure2strokespirit.net/forums/proxy.php?request=http%3A%2F%2Fforum.ibike.com.hk%2Fimages%2Fsmilies%2Fdefault%2Fem04.gif&hash=5efab50c4cee6b4be3168c8881835a06569c529b)  you know more about this airbox than I do.

This is basically a SPR airbox... Anyone have a SP airbox for comparision?

EEKNOWS: You are right, it's all the way from the snorkles to the end of the exhaust pipe.. 

zoomzoom: as I see it - our target are to increase the speed of air in the complete engine...one example are the chrankshaft of the 3MA1/2/3/5 versus the 3MA4 SP. The 3MA4 has, apart from a better balance, a bigger volume in the same chrankcase = more pressaure of air = more speed what is needed to accept the SP porttiming,(cylinder 20) and the SP exhaust venturi in the cylinder..
for sure the angels of the tranferport in the cylinder are important, as well as many other points - in my oppenion..

your point 1 : equal to what vaccum you decide to have to fill the chranchase
your point 2: that is my point - in the complete engine
your point 3: my experiance are not like you describe - but if you have another oppenion it's ok with me.

Quote from: Neal on January 24, 2013, 02:41:09 PM
Have you guys seen the "trumpets" that fit onto open carbs ? They are supposed to help with improving the velocity of the incoming air . The same principle if you have a 2L bottle of water - when you swirl it around and flip it upside down the water exits much faster .

There were some experiments by the legendary prof. Blair on the subject.
Wouldn´t belive it blindly though, there are a lot of clever people stating that intake flow never reaches sonic speeds, and in this document I can see numbers higher then mach2.
http://www.profblairandassociates.com/pdfs/RET_Bellmouth_Sept.pdf

mbsteve, that is a nice article, please don´t get me wrong, not trying to shoot anything down here, but...
That formula, seems to have it´s roots in helmholtz resonance formula?
If so, there is a problem imo. One hears a lot about helmholtz resonance on a 2stroke engine, but the basic helmoltz resonace does not apply on a 2stroke engine.
Specific helmholz resonance calcultions, apply to a set of parameter that are not all present in a 2stroke engine, neither in the airbox of a 2 stroke engine.
It has to do with superfast pressure changes in an enclosed system (or better with only one opening, like a beer bottle f. exe.)
Now, a 2 stroke airbox is not an enclosed system. Sometimes there is a way to the crankcase, sometimes there is a way to the cylinder... and exhaust... and the atmosphere... and the outer space :)
So, helmholtz resonance (or derived) formulas maybe do not apply?
But maybe that formula accounts for that, I don´t know. I have a set of R airboxes laying around, it would be interesting to mesure them, and see what the result is when the numbers are dialed in that formula.

And I actually got an idea that maybe could work, and maybe not so hard to test.
Here is the background:
http://www.youtube.com/watch?v=K4Acofm09EA
From 0.35 to 0.42 there is a sequence of 4 accelerations where it is clear that back flow is happening.
To the best of my understanding this happens because of a pressure diferential when crankcase is pressurised, and the reeds are still open - backflow occours.

Relating this to the airbox. Well, if "back flow" occours at the airbox intake at an rpm regime where the motor is intend to work good, f.exe. the powerband, then probably there is something wrong.
This could maybe be tested by reving the engine under load, with a thin piece of paper hanging close to the box intake. That would maybe tell what is happening with airflow at the box intake.

Quote from: casal-fan on January 25, 2013, 12:28:28 AM

Relating this to the airbox. Well, if "back flow" occours at the airbox intake at an rpm regime where the motor is intend to work good, f.exe. the powerband, then probably there is something wrong.
This could maybe be tested by reving the engine under load, with a thin piece of paper hanging close to the box intake. That would maybe tell what is happening with airflow at the box intake.

Now there is a realtime basic test that might show what the airbox is doing at different points in the rev range.
Easy to do on a dyno, although not super accurate, it will indicate at what rpm the box flows best.

I would still like to know if any of the theory in this thread was known and incorporated into the design of our machines produced 20 odd years ago.....

Quote from: Need4speed on January 24, 2013, 11:52:26 PM
EEKNOWS: You are right, it's all the way from the snorkles to the end of the exhaust pipe.. 

zoomzoom: as I see it - our target are to increase the speed of air in the complete engine...one example are the chrankshaft of the 3MA1/2/3/5 versus the 3MA4 SP. The 3MA4 has, apart from a better balance, a bigger volume in the same chrankcase = more pressaure of air = more speed what is needed to accept the SP porttiming,(cylinder 20) and the SP exhaust venturi in the cylinder..
for sure the angels of the tranferport in the cylinder are important, as well as many other points - in my oppenion..

your point 1 : equal to what vaccum you decide to have to fill the chranchase
your point 2: that is my point - in the complete engine
your point 3: my experiance are not like you describe - but if you have another oppenion it's ok with me.

yeah neal i agree in some respects, but hey its all good if she share opinions and info..

Quote from: Crank on January 25, 2013, 07:28:53 AM

Quote from: casal-fan on January 25, 2013, 12:28:28 AM

Relating this to the airbox. Well, if "back flow" occours at the airbox intake at an rpm regime where the motor is intend to work good, f.exe. the powerband, then probably there is something wrong.
This could maybe be tested by reving the engine under load, with a thin piece of paper hanging close to the box intake. That would maybe tell what is happening with airflow at the box intake.

Now there is a realtime basic test that might show what the airbox is doing at different points in the rev range.
Easy to do on a dyno, although not super accurate, it will indicate at what rpm the box flows best.

Crank, im picking up my dyno tommorrow mornig and once sorted we can start doing doing some testing.....

Quote from: Crank on January 25, 2013, 07:28:53 AM

Quote from: casal-fan on January 25, 2013, 12:28:28 AM

Relating this to the airbox. Well, if "back flow" occours at the airbox intake at an rpm regime where the motor is intend to work good, f.exe. the powerband, then probably there is something wrong.
This could maybe be tested by reving the engine under load, with a thin piece of paper hanging close to the box intake. That would maybe tell what is happening with airflow at the box intake.

Now there is a realtime basic test that might show what the airbox is doing at different points in the rev range.
Easy to do on a dyno, although not super accurate, it will indicate at what rpm the box flows best.

Hummm, sometimes, finger can be fast a typing...
While this test could be interesting to do, if the findings are not very good, and a lot of inconsistency shows at the airbox intake, it could be that the undesired effects have they roots somewhere else either then the airbox.
And now, I´m probably gonna walk into deep water here, without knowing a heck of a lot about swimming... but anyway...

Resonances in an engine are supposed to play a major role. While (at least to my knowledge) it would be very difficult to quantify them in an empirical manner, the theorys still apply.
F.exe. if looking at the crankcase filling, the intake period.
A depression is caused in the crankcase a column of  mixture rushes into it. At some time, the low pressure area in the crankcase becomes a high pressure area. Since mixture (as well as other matter) flows from high to low pressure areas, then the direction of the flow would be reversed.
Now, the time this event (in and out of the crankcase) takes, is a frequency.
This frequency can be matched, by adjusting a handfull of variables, all playing a role upon eachother.
Some of the variables I can think of would be, crankcase pressure, inlet length (this is a trycky one... what is inlet length?, with an airbox, is the airbox part of the inlet? Is it not? Have no idea), carburetor diameter.

Assuming f.exe. an engine is rotating steady at 6000rpm. If intake frequency is matched exactly for 6000 rpm, that would mean that the crankcase would have optimal filling in every rotation. The stream thrugh the carb would be constant, and no intake adverse happenings would occour.
Now, to quantify this? Well, helmholtz resonance would be the one, IF the crankcase was sealed, and had a steady volume. That of course does not happen, crankcase opens to transfers, and the piston running up and down makes sure that the crankcase volume is constantly changing. Quantifying, like in putting all this into a formula? I don´t think so... but that doesn´t mean that a good result can be obtained by playing with helmholtz resonance principles.

So, hurra, now one can test to death, and have an engine that is perfectly tuned for lets say 6000 RPM.
Now, all that is needed is to not go out of 6000rpm, because as soon as that changes, the engine frequency changes, and the well tuned intake frequency for 6000RPM will no longer work at its best.
So, if the TZR engine (as well as any roadgoing engine) must operate in a vast rpm range, compromises have to be made, and mesures to atenuate the bad performance in rpm regimes where nothing sings along have to be taken.

Coming back to the airbox.
If a manufactor designs an engine that is supposed to be a sports engine (but still for the road, and it has to go around a city at 4-5k rpm otherwise reviews will shoot it down), after parts have been chosen (carb, etc) intake testing has been done to satisfy the wish of a sports, revy engine, then he will probably meet up with an utter shity low rpm range. But lucky, he has the airbox. He has the airbox, and the oportunity to tune the airbox to a frequency that will somehow interact with the hole engine and intake (without airbox) frequency, and improve engine performance at the ranges where it was not happy.
And while this can be tottaly wrong, (its just an opinion in a forum, and not a cientific document), many repports around that when taking the airbox out, engine will loose at lower rpm regimes.

And to finish, just a practic experiment to see how this all thing MAYBE works.
A bottle, blow air into it by its neck, notice the sound.
Half filled with water, or beer :) - higher frequency
Insert a tube in the bottles neck so that it works as if the neck was made longer - lower frequency
Inset a tube trugh the neck that has a small inside diameter - lower frequency

Back flow out the carb is more to do with the intake tract resonances,

Quote from: EEKNOWS on January 27, 2013, 04:21:31 PM
Back flow out the carb is more to do with the intake tract resonances,

Agree.
I just wonder if having the airbox as some kind of independant resonation element, would somehow "counteract" rpm areas where frequencys are inadequate.
Did some "homework" during the weekend, on this, and ended up with more questions then answers. (It usually goes like this).

Eeknows, what is it you refer to as intake tract? Is it the combo crankcase-carb bell mouth-and everything in between?
And another one, the aprilia 125 you tested with and without snorkels, did it have the 28mm carbs?

Bellmouth to reed tip I would call the inlet tract on a reed engine. Aprilias has a 34mm VHSB, hoping to trial the 28mm and get similar HP/torque with better fuel economy.