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Discussion Starter #1
I had my airbox off last weekend and a riding buddy was looking at it and reckons I should remove the two intake snorkels as it will let more air in and create more power.
I suggested that this was old school carburetor style thinking and that Kawasaki could easily have made the snorkel diameter bigger if they thought the engine needed more air.

I would be interested to hear from anyone learned on this subject.

They are shown in the picture below of my airbox with the lid off. Note they are the two smaller tubes to the right in the photo., not to be confused with the larger throttle body intake tubes which are a tuned length.

P1000164.JPG
 

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My guess would be that those snorkles are probably there to help with lowing the intake noise. On my z125, when I took the intake box off, it made the bike sound really loud but the sound was coming from the intake. With that, I'm guessing those were added to help give the sound Kawasaki wanted to have for these bikes.
 

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Discussion Starter #4
Excellent question, No idea. In theory larger intake will allow for more flow/pressure which should increase power, no?
From the little I know you get more velocity (air speed) with a smaller diameter due to less surface area friction and also I read on the Ninja 300 forum that the snorkels calm the air flow so it is not so turbulent inside the air box. It also appears that you only need a whole heap of air for really high revving engines (probably 4 cyl) that rev to 15K and beyond which is why some of those bikes have RAM air intake systems taking air from the very front of the bike.

My guess would be that those snorkles are probably there to help with lowing the intake noise. On my z125, when I took the intake box off, it made the bike sound really loud but the sound was coming from the intake. With that, I'm guessing those were added to help give the sound Kawasaki wanted to have for these bikes.
Yes I would agree with that, those Euro 4 tests are very strict on noise these days. Dam bureaucrats!
 

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The redesigned airbox and dual intakes on the N4 have been painstaking engineered by Kawi to maximize engine performance...IMHO modifying their work will not deliver good results............
 

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The redesigned airbox and dual intakes on the N4 have been painstaking engineered by Kawi to maximize engine performance...IMHO modifying their work will not deliver good results............

Were not discussing the throttle-body snorkels which will have a significant impact if modified but the air-box inlet snorkels, on the CBR1000 there was a trap door for the intake that opened above 5000 rpm the manufacturer claimed it increased low end torque.
That was thew first thing I tore off my CBR1000RR, it was called the flapper mod. Afterwards the engine sounded much nicer and if there was a loss of torque my butt dyno could not tell
 

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From the little I know you get more velocity (air speed) with a smaller diameter due to less surface area friction and also I read on the Ninja 300 forum that the snorkels calm the air flow so it is not so turbulent inside the air box. It also appears that you only need a whole heap of air for really high revving engines (probably 4 cyl) that rev to 15K and beyond which is why some of those bikes have RAM air intake systems taking air from the very front of the bike.



Yes I would agree with that, those Euro 4 tests are very strict on noise these days. Dam bureaucrats!
The inlet snorkels are covered by the air filter correct? if so the air has to pass thought the filter before getting to the throttle bodies. I would think the filter would do a pretty good job of calming any turbulence. I honestly believe if you gutted the bottom of the intake so it was wide open, the only thing you would get is a better sounding bike and maybe a very insignificant power increase as well.
 

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Discussion Starter #8 (Edited)
I had a feeling this thread might create confusion... :confused:

@xplorguy I'm talking about these inlet snorkels:

P1000196.JPG

P1000195.JPG

@mad_mardigen That's interesting about the flap on the CBR and the subsequent removal of. I'm erring away from not removing the inlet snorkels as they weigh next to nothing and I can't see how any significant gains could be had. It appears Kawasaki has put some time into improving the air intake system over the 300.
Here's the official press release blurb about that part of the engine:

Significant performance gains are due to the new downdraft intake, which increases performance especially at high rpms and larger air box, which offers increased intake efficiency. The downdraft intake utilizes the shortest and most direct path for air to enter the cylinder, which improves cylinderfilling efficiency and contributes to increased engine power, especially at high rpm. Airbox volume has been significantly increased to 5.8 liters. The new airbox features revised rigidity at the top of the airbox, which eliminates unwanted noise, enabling riders to more clearly hear the engine’s intake note
when accelerating. Different height intake funnels contribute to the engine’s smooth response by allowing torque valleys to be tuned out.
 

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I had a feeling this thread might create confusion... :confused:

@xplorguy I'm talking about these inlet snorkels:

View attachment 1357

View attachment 1359

@mad_mardigen That's interesting about the flap on the CBR and the subsequent removal of. I'm erring away from not removing the inlet snorkels as they weigh next to nothing and I can't see how any significant gains could be had. It appears Kawasaki has put some time into improving the air intake system over the 300.
Here's the official press release blurb about that part of the engine:

Significant performance gains are due to the new downdraft intake, which increases performance especially at high rpms and larger air box, which offers increased intake efficiency. The downdraft intake utilizes the shortest and most direct path for air to enter the cylinder, which improves cylinderfilling efficiency and contributes to increased engine power, especially at high rpm. Airbox volume has been significantly increased to 5.8 liters. The new airbox features revised rigidity at the top of the airbox, which eliminates unwanted noise, enabling riders to more clearly hear the engine’s intake note
when accelerating. Different height intake funnels contribute to the engine’s smooth response by allowing torque valleys to be tuned out.

I'm having a hard time understanding the need for an air box with this design, most bikes with an air box have ram air and the box is utilized to increase intake pressure. The faster you go more pressure.
The only reason I see for this air box is to be able to mount the flat air filter, You could probably remove the whole air box and just mount some old style K&N carburetor air filters to each throttle body snorkel and get the same if not better results. ------ downdraft intake, id like to see that in a wind tunnel :wink:

I wouldn't do it, just saying for arguments sake
 

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My $.02

I'm having a hard time understanding the need for an air box with this design, most bikes with an air box have ram air and the box is utilized to increase intake pressure. The faster you go more pressure.
The only reason I see for this air box is to be able to mount the flat air filter, You could probably remove the whole air box and just mount some old style K&N carburetor air filters to each throttle body snorkel and get the same if not better results. ------ downdraft intake, id like to see that in a wind tunnel :wink:

I wouldn't do it, just saying for arguments sake
Gents let me start off by saying that KHI did a phenomenal job with this aribox. Those of you that have owned 600cc+ bikes and had done work with their airboxes will notice right off the bat that KHI made the Ninja 400 airbox just like the ZX-6R or ZX-10R airbox. The air filter is HUGE for a 399cc bike. Also unequal length snorkels are only seen on bigger more expensive bikes. The fact that it has not 1 but 2 inlets to the airbox is also a huge leap for the smallest Ninja. My 2010 and 2012 FZ1's airbox inlet was just about the same size of the combined inlets to the Ninja 400s.....Thats why almost every 2007-2014ish FZ1 owner does the LARS airbox mod which is essentially opening the bottom of the airbox. I will say that I have the MWR airfilter on my bike and the difference in sound is HUGE...almost as loud as my 2 brothers exhaust. This airbox has been tuned to the T and I would not dare modify it since it is extremely well egineered in my eyes. One **** of an airbox for such a small engine...Dont touch it!
 

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I had my airbox off last weekend and a riding buddy was looking at it and reckons I should remove the two intake snorkels as it will let more air in and create more power.
I suggested that this was old school carburetor style thinking and that Kawasaki could easily have made the snorkel diameter bigger if they thought the engine needed more air.

I would be interested to hear from anyone learned on this subject.

They are shown in the picture below of my airbox with the lid off. Note they are the two smaller tubes to the right in the photo., not to be confused with the larger throttle body intake tubes which are a tuned length.

View attachment 1341

I am more interested in what is going on with the velocity stacks. Can you take a picture wider out? I have tested velocity stacks, and found that the big change is that you are moving the torque peak. Shorter = higher rpm. But, on the 400, which should have equal length intakes, it looks like different length stacks per cylinder, and I find that interesting. With no other mods, that would mean that each cylinder is tuned for a different rpm. On a Busa or 14, the outer intake length, in the cylinder head, is longer. Hence, using a shorter velocity stack on the outside will somewhat equalize the tuning.

As for the intake snorkels, as has been mentioned, probably a lot to do with reducing noise...however, tuning an airbox is sort of like tuning a subwoofer...big ports are tuning for a lower frequency (hz/rpm). I have done a lot of dyno work while swapping parts right on the dyno, and this is the only way you can test these mods reliably, imo....short of doing it at the track. If it were me, I'd put it on the dyno...and swap parts to test it.

Oh, and on another note, at the speeds this bike can achieve, you wouldn't get much gain from a pressurized intake; the gain would be from the cooler intake air.

Downdraft intake refers to the fact that the cylinder/head are canted forward, in order to straighten the intake tract. A great example of one of the pioneer street bikes for this is the 1985 Yamaha FZ750.
 

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I am more interested in what is going on with the velocity stacks. Can you take a picture wider out?

Oh, and at the speeds this bike can achieve, you wouldn't get much gain from a pressurized intake; the gain would be from the cooler intake air.

Downdraft intake refers to the fact that the cylinder/head are canted forward, in order to straighten the intake tract.
Funny you mention pressure. The larger airbox in the Ninja 400 and the long air inlet tubes actually increase the speed in which the airbox is filled thus possibly creating a slight positive pressurization under the Helmholtz resonance principle. Downdraft intakes are mainly on supersport engines. It's referring to the path the air goes into the throttle body, and has nothing to do with the forward canting of the engine. Also, MWR recommends changing the longer velocity stack for another shorter one to maximize the added airflow of their filters at maximum RPMs.
 

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Funny you mention pressure. The larger airbox in the Ninja 400 and the long air inlet tubes actually increase the speed in which the airbox is filled thus possibly creating a slight positive pressurization under the Helmholtz resonance principle. Downdraft intakes are mainly on supersport engines. It's referring to the path the air goes into the throttle body, and has nothing to do with the forward canting of the engine. Also, MWR recommends changing the longer velocity stack for another shorter one to maximize the added airflow of their filters at maximum RPMs.
The cylinder is canted forward in order to allow for the straighter cylinder head intake ports. A throttle body is practically always straight, by design. A cylinder head intake port is not.

"Helmholtz resonance principle" is a fancy way of describing the "subwoofer tuning" that I was talking about. Got plenty of books on it. :)
 

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The cylinder is canted forward in order to allow for the straighter cylinder head intake ports. A throttle body is practically always straight, by design. A cylinder head intake port is not.

"Helmholtz resonance principle" is a fancy way of describing the "subwoofer tuning" that I was talking about. Got plenty of books on it. :)
Brother....manufacturers don't cant the engines for a downdraft intake system...they do it to lower the center of gravity. With fuel injection downdraft intakes exploit this characteristic. You can't say that the engines are specifically canted forward for the intake design..that's not the main reason. Take a look at the Ninja 250/ 300. They are slightly canted forward and do not have downdraft intakes. I've owned both. Another example that pops to my brain is the CBX or other aircooled bikes from the 70's and 80's. The FZR 750 Genesis engine was canted forward for 2 reasons..lower center of gravity and the fact that it was the first motorcycle engine with a stacked transmission.

And yes...I didn't read your previous post where you had mentioned "subwoofer Hz"...I skipped to the last page...LOL. It's the same thing.
 

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Brother....manufacturers don't cant the engines for a downdraft intake system...they do it to lower the center of gravity. With fuel injection downdraft intakes exploit this characteristic. You can't say that the engines are specifically canted forward for the intake design..that's not the main reason. Take a look at the Ninja 250/ 300. They are slightly canted forward and do not have downdraft intakes. I've owned both. Another example that pops to my brain is the CBX or other aircooled bikes from the 70's and 80's. The FZR 750 Genesis engine was canted forward for 2 reasons..lower center of gravity and the fact that it was the first motorcycle engine with a stacked transmission.

And yes...I didn't read your previous post where you had mentioned "subwoofer Hz"...I skipped to the last page...LOL. It's the same thing.
Canting the cylinder forward allows for a straighter intake tract. Pretty simple. I did not say it was the sole reason for doing so, but in the terms of intakes, of which we are speaking, it is a design consideration....and can lead to more power. A lot of times, when you Google the FZ750, you might not get all of the pertinent info. As far as air-cooled bikes of the 70's and 80's....I don't recall too many with 45 degree canted cylinders and straightened intake ports...there are probably a few, for sure?? I shopped around on CBX's, but just too expensive, now.

Also, there is no doubt, that with equal diameter ports, a longer intake tube, or stack, is tuning for a lower...not higher, frequency.

I have a 300 Ninja, 400 Ninja, and have owned a 250 in the past, also. That doesn't make me an engineer, lol. But, I do have some experience.

Anyway, I just want to see some more pics of those velocity stacks!
 

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Discussion Starter #16
Canting the cylinder forward allows for a straighter intake tract. Pretty simple. I did not say it was the sole reason for doing so, but in the terms of intakes, of which we are speaking, it is a design consideration....and can lead to more power. A lot of times, when you Google the FZ750, you might not get all of the pertinent info. As far as air-cooled bikes of the 70's and 80's....I don't recall too many with 45 degree canted cylinders and straightened intake ports...there are probably a few, for sure?? I shopped around on CBX's, but just too expensive, now.

Also, there is no doubt, that with equal diameter ports, a longer intake tube, or stack, is tuning for a lower...not higher, frequency.

I have a 300 Ninja, 400 Ninja, and have owned a 250 in the past, also. That doesn't make me an engineer, lol. But, I do have some experience.

Anyway, I just want to see some more pics of those velocity stacks!
Dont stop now, I just got me a big thing of pop corn!

https://giphy.com/gifs/popcorn-movie-nothing-RHiD0K65NxxLO

Sorry, the airbox is all closed up and fuel tank back on so no more pics of velocity stacks.
 

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snorkels

Hi guys,
I basically joined this forum just to give my 2 cents regarding the Snorkels topic. Over the years i owned many bikes with and without snorkels and put a bunch of them on the dyno to see the difference of power between mods.

Basically removing the snorkel makes the bike more responsive and always makes more power and torque in the low-mid range but never increase your peak power...Manufacturers are bright enough to make them the right size so that they flow well enough at the top end to make max power but they are a restriction in the low rpm when the engine does not suck the same quantity of air.

Kawasaki usually put dual throttle valve on bikes with big throttle bodies to smooth low end power and make the bikes easier to ride (for exemple the Z650, z900 and the z1000 but nore of these bikes with the same style of airbox as the ninja 400 have snorkels), but since the ninja 400 doesnt have dual throttle a snorkel is a way to make the bike more predictable and easier to ride. Another way would be to have a fly by wire system (like the zx10r or in this class of bikes the ktm 390 duke or rc390) so that you can map you throttle to be more progressive.

Two Easy examples of what is to be gained by simply removing the snorkels without touching the airbox (drilling holes etc...) are my sv1000s and fz-07.

On the sv1000 removing the snorkel have this effect on power on the dyno:
http://www.chewys-stuff.co.uk/tank_spacers/Dyno1.jpg
Snorkel removal adds torque! - SV1000 Portal

On the fz-07 Dynojet Power Commander V - INSTALLED!!! | Yamaha FZ-07 Forum

There are tons of bikes with snorkels and basically they all do the same job, they limit the noise and make the bike easier to ride.

The bike could be running a little bit leaner after removing the snorkels so its a good idea to dyno before/after if youre considering running the bike like that.

Hope it helps.
 

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Short stack is generally used for peak power while the long stack helps increase bottom/mid range power. I've done a lot of intake testing over past few years.

Here's just a few things I found on the dyno last month -

- Don't even bother with an aftermarket filter. Remove the backfire screen and call it a day. I dyno'd with the "modified" stock filter and without a filter at all and the graph is dead even.
- I plugged one of the front snorkels on the airbox to see if it would reduce the power for the **** of it. Hardly phased it on the graphs. Less than a half hp if I remember right.
 
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Short stack is generally used for peak power while the long stack helps increase bottom/mid range power. I've done a lot of intake testing over past few years.

Here's just a few things I found on the dyno last month -

- Don't even bother with an aftermarket filter. Remove the backfire screen and call it a day. I dyno'd with the "modified" stock filter and without a filter at all and the graph is dead even.
- I plugged one of the front snorkels on the airbox to see if it would reduce the power for the **** of it. Hardly phased it on the graphs. Less than a half hp if I remember right.
I was wondering if it had a screen on it, or was just pleated. On my 14R I got 3 hp from removing the screen. Solid mod! Interestingly, the 14R lost power with no filter; presumably from turbulence in the box. Short stacks on a 14 or 14R will bump the torque peak by 300 rpm. I find it interesting that there are two different sized stacks on the 400; you would think that the intake ports themselves would be symmetrical. On some of the bigger motors, the outer two ports are longer, and so it is clear why they would use shorter velocity stacks on the outer two cylinders.
 
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