Shortening intake runners/enlarging opening

quarterliter · June 27th, 2013, 04:11 PM

Anyone tried this? I believe the stock ones are meant for noise reduction and less for performance? Should I shorten the stock length stacks or bore the opening(which in turn deletes the stacks completely)

agent of orange · June 27th, 2013, 06:14 PM

you would have to tune the carbs for it. shorter stacks will give you higher peak hp number but you will reduce your low mid range torque. i think thats how it works.

agent of orange · June 27th, 2013, 06:16 PM

or you mean the carb to head boots? as the 250 has pretty long ones and the diameter matches the bore of the carbs

quarterliter · June 27th, 2013, 06:48 PM

Orange i was talking about the insert that goes into the top of the airbox. The lid sort of thing. I might shorten them up but im just trying to figure out if I want to make the openings bigger b/c the carbs opening is larger than these holes.

DaBlue1 · June 27th, 2013, 06:55 PM

Quote:

Originally Posted by quarterliter

Orange i was talking about the insert that goes into the top of the airbox. The lid sort of thing. I might shorten them up but im just trying to figure out if I want to make the openings bigger b/c the carbs opening is larger than these holes.

See this thread. http://www.ninjette.org/forums/showthread.php?t=79318

quarterliter · June 27th, 2013, 06:59 PM

Do you see the curves heading into the runner on the stock one? I want to keep those I think the dimensions were designed to help with flow. I was thinking of boring then out keeping some of those angles but increasing the area of the openings. But i would lose all the runner length as boring it would get rid of them.

quarterliter · June 27th, 2013, 07:02 PM

^in the link that Dablue posted

choneofakind · June 27th, 2013, 07:53 PM

I cut those out with good results. The bike really seems to like it. Just remember to shim your needles a tad. Currently, I'm running an open intake lid, full exhaust, and fuel injection. The air still seems to be smooth because it gives consistent performance. I ran the same setup with carbs and got good results as well.

Throttle response in the mid-range is a touch better, top end is a touch better, sounds good as well. Not sure how much of this is the intake change vs how much is the jetting change.

here's a picture:

choneofakind · June 27th, 2013, 07:57 PM

Just curious here Kevin,

have any of your little changes (sanding, etc) actually made any noticeable difference? I honestly thing a clean air filter and a little jetting help would make more difference than sanding the inside of the air box

quarterliter · June 28th, 2013, 06:57 AM

I just had the air box off anyways....but regardless haha I do all sorts of little things that I believe add up. I raced another 250 a little while ago and my bike pulled noticibly harder. Granted I am only 135 lbs

choneofakind · June 28th, 2013, 10:04 AM

I'm light also, no worries. Right around 135 without gear on.

Go for it with the intake lid! One trick I found was that if you sand the edge you cut, then brush it lightly with the flame from a blowtorch/lighter, then edge melts just a tad, and really cleans up all the plastic burrs/whatever from sanding. Not necessary, but looks a lot better. This goes for any cuts you make to ABS plastic.

voidrider · June 29th, 2013, 07:55 PM

Those tubes are actually called Helmholtz Resonators. They actually serve a (albeit minor) purpose.

Just for informational purposes...

The overall concept is that air is of course a fluid. The valves/piston draw air into the carbs, you can sort of think of each "draw" as a pulse or "blob" of air. Its sort of weird to think about, and it goes into the realms of laminar and non-laminar flow in fluid mechanics, but simply put, if a fluid is traveling smoothly through a pipe or system, and not "bouncing against all the other blobs of air", you get more air through the system. (Its actually more about pressure waves and regions, but the pulse/"blobs" model works). The length and diameter and even the angles of the resonators are "tuned" to help the air move through the carbs and into the engine head with good flow.

But its not even that simple. You want laminar flow to get high volume of air into the cylinders, but you want "the right amount" of non-laminar flow downstream of where fuel enters the system to get a good fuel air mix. There are some videos and computer animation that show the atomization of fuel and how the flow moves though the valves and into the cylinders.

Overall its a pretty good system, and anymore its getting near to an exact science, but the design engineers usually don't design for "performance", a lot of thought goes into reliability, a "level of of functionality" and probably a half dozen other criteria with all the compromises that comes with that sort of thing.

Are they necessary? Obviously not! Its just that a poorly designed system with "bigger pipes" is not necessarily more free flowing. It could have bends and reflection points that actually cause less flow. I have a hard time understanding how the Resonators do much good with the air filter in the way, but its supposed to be "tuned" to the size of the airbox, and the volume of air the engine draws per air intake cycle.

I think it would be nice to have a system in a wind tunnel type system with smoke and high speed video to actually make visible the pressure waves in systems, like pods, an airbox with no lid, stock airbox, etc. Then you could do a cross reference of carb adjustments. Following that with dyno tests would be great, and that is pretty close to what the big racing team engine guys are doing between races. From that sort of testing you could pull the data off that applies to your style and type of riding.

The system the engineers came up at KHI is what comes stock, its good for most riders under most conditions for most riding styles. Knowing how/why they arrived at their design, and what criteria they used would be valuable knowledge. Since we don't have that, studying the system they arrived at is a good step in knowing what modifications will give the biggest benefit.

If you go to a more free flowing exhaust, its does very little good unless you can supply more fluid into the system, and the reverse is also true. If you don't balance the in and the out you will not really get the full advantage of your alterations.

choneofakind · June 30th, 2013, 11:06 AM

Good info Sam!!

Yes, I knew about the intake resonances and why those tubes are there, but the bike does seem to respond very well with a full exhaust and the intake lid opened.

In a perfect system, those resonances can be very helpful. My question is; does opening the intake lid ruin those pressure waves in the air? There is still a solid back, and still a long flow of air for the waves to travel along. It would seem to me like opening the intake lid would not ruin the ability of the pressure waves to bounce back and forth in the air box. It also seems to me like the foamy OE filter would dampen some of those so that it really doesn't matter either way.

You talk about laminar flow and getting the correct proportion of dirty air to mix fuel and air; one of our members from Greece with OE FI setup mentioned drilling holes in the air box in opposing corners in order to create a 'swirl' pattern inside the air box. Do you think this would be beneficial to mixing air and fuel consistently?Judging by how much better my fuel injection setup runs with the air box compared to a pod filter, I assume that the air box with the opened intake lid provides more clean air flow than a pod filter. However, I'm also willing to try small things to help that out however I can.

I'm asking questions because I'm curious, and I hope to stimulate some conversation from users who know what they're talking about and can help us all learn. Let me know what your thoughts are on this.

voidrider · June 30th, 2013, 02:36 PM

I realized that another example of Helmholtz resonators that some riders may be familiar with are velocity stacks on autos. I have heard of the engine guys on race teams changing them out depending on air temperature, since temperature changes the air density. But let's face it, that is trying to get that last 1 or 2 percent of performance.

Quote:

Originally Posted by choneofakind

My question is; does opening the intake lid ruin those pressure waves in the air? There is still a solid back, and still a long flow of air for the waves to travel along. It would seem to me like opening the intake lid would not ruin the ability of the pressure waves to bounce back and forth in the air box. It also seems to me like the foamy OE filter would dampen some of those so that it really doesn't matter either way.

Here is where I must admit a good deal of confusion myself.

My understanding is that the most problem causing waves which tend to choke off the fullest possible flow come from the valves opening and closing. The piston draws air into the cylinder, the valve closes. Suddenly there is no place for the air that was just about to enter the cylinder to go. The air 'behind' that bit of air still has momentum, which results in a higher pressure region. A pressure wave is generated which moves back towards the carburetor as the moving air continues to pile into the now non-moving air. Its similar to a sound wave moving against the flow. Another less accurate model I have run across about bad pulse flow uses a chain-reaction pile-up on the freeway.

Tuning in this realm is all about controlling the flow to minimize the "piling up" effect. If you have a conveyor belt you want the spacing between, say boxes to be right. The boxes need to be the right size and shape and spaced right. Convert that to volumes of air that moves in very rapid pulses in a tube or enclosed system. The resonators control the size and spacing. The move towards more valves in engine design is somewhat analogous to adding more conveyor belts.

You mention the filter. Yes it would have a dampening effect, but a really good system designer could account for that dampening effect. I have to wonder if at the given pressures the foam filter becomes incidental, like a screen in a window? It keeps the bugs out, but despite actually making the window effectively smaller, the wind still blows through it nearly unimpeded. If you have someone waving an old fashioned fan on the other side of the screen you still feel the "pulses" of moving air. But, in the airbox/carb system, I am honestly not sure.

Quote:

Originally Posted by choneofakind

You talk about laminar flow and getting the correct proportion of dirty air to mix fuel and air; one of our members from Greece with OE FI setup mentioned drilling holes in the air box in opposing corners in order to create a 'swirl' pattern inside the air box. Do you think this would be beneficial to mixing air and fuel consistently?Judging by how much better my fuel injection setup runs with the air box compared to a pod filter, I assume that the air box with the opened intake lid provides more clean air flow than a pod filter. However, I'm also willing to try small things to help that out however I can.

I am unfamiliar with the FI systems on the newer Ninjas, so what follows is mostly WAGs on my part. The "swirl' of air in the airbox would need to be beneficial to how the air moves from the airbox into the rest of the system. The shape and volume of the airbox and the size and positioning of holes would probably all influence the flow to some degree. Dyno testing would show if there is a benefit, but it would take something like the high-speed photography/dozens of pressure sensors arranged throughout the airbox recording in real time to show what is going on to create the benefit.

Your description of your bike running better with the airbox than pods is not necessarily due to the pressure waves being able to bounce back and forth in the airbox, or even having a more free flowing system. Its likely that having the airbox in place is helping the tune of the system. Again that is sort of like sizing the pulses of air going into the airbox to match the size of the air pulses leaving the airbox, which is defined by the conditions downstream...all the way at the intake valves. I think of it a bit like those timing lights that limit the number and spacing of cars as they move onto the freeway. Consider that the volume and frequency of the pulses generated by the air moving through and being blocked by the intake valves has a certain frequency range, from idle to full throttle. Everything upstream of that needs to be in 'harmony' to prevent the pulses of air from having continuous collisions. If the system is tuned only to one end of the frequency spectrum or the other it will be sharp or flat in respect to the ideal. Since the frequency in changing there is no perfect design, so the system is designed to work the best across the entire operational frequency range. if someone ends up riding most of their times at high revs, the stock system is not the best for them.

A lot of the concerns about the laminar (most volume) flow to non-laminar (more turbulent to mix fuel and air) depends on where the fuel injectors lie in the system. The injectors themselves are designed to atomize the fuel better than the venturi effect in carbs. They just make a finer spray of microdroplets. You aren't using a change in pressure to do that job as much. I would surmise a FI system could have nearly laminar flow throughout the intake system. It would definitely be able to flow more air without leaning occurring, since the fuel amount would be in tune with the greater air flow.

Your described approach is exactly spot on. If you had various air boxes you could design an experiment where you alter only one thing at a time, dyno the bike with that particular alteration, record the results and repeat. Of course it gets hard when you start exploring the interactions where change A showed an improvement, but change B showed worse result, but using both seems to be a benefit? That's where the higher level mathematics that people say "you will never use that in the real world" gets used with great results, in fact its the only way to get quantified repeatable results when dealing with complex systems. If you want to get more into that, I will have to bring my wife into it, because she is the math genius in our family!

Quote:

Originally Posted by choneofakind

I'm asking questions because I'm curious, and I hope to stimulate some conversation from users who know what they're talking about and can help us all learn. Let me know what your thoughts are on this.

I'll try to help, even though my background in engineering is more mechanical and manufacturing. If you could find someone who is more into aeronautical engineering, or a specialist in fluid dynamics, then you could get really knowledgeable replies.

The stock systems are good, but are the results of hundreds of compromises. Engineers like easy, and sometimes the easy solution is not the best. Overall, most modifications marginally improve some aspects of a system and usually compromise some other aspect, more power but lower fuel economy for instance.

You always risk "Correlation does not imply causation" errors in these discussions - "more powerful engines are louder, so if I make my engine louder it will be more powerful"

"Butt dyno" is too subjective.

Overall, the airbox is about having a "reservoir of air" sufficient to supply the piston draw. Tuning for the timing and volume of the pressure waves determine the size shape and location of the intakes into the airbox. The point is to allow air to enter the system so it as close as possible to being "in synch" with the waves the system is generating.

Sorry for the long replies. Your short questions and comments are actually quite complex, and I feel deserve my trying give thoughtful replies. If someone out there does work in fluid dynamics or the like and cares to add, I would love it. I hate to find I am spreading bad information or have made the error of holding onto outdated data.

If this is too verbose and no one else wants it, we could take this to PM as well.

choneofakind · June 30th, 2013, 06:09 PM

Sam, that was one awesome post! Thanks for the time and thought you put in on that.

I'll be keeping this topic in the back of my mind when I go through Fluids class this year. (Starting my junior year of ME at Ohio Northern University this fall) Hopefully I can pick my prof's brain a little bit on the topic of air boxes and swirling air and air filters. My understanding of this is basically modeled by a slinky being compressed and extended longitudinally; you'll see the 'piling up' and you'll see the 'wave' transfer along the length of the slinky. However, my slinky model only accounts for the 'tube' section of the air box (into the carb/throttle body) and does not really account for the volume of still air in the box, or the effect of the filter on the wave. Once I get to that part, I get kinda lost.

DaBlue1 · July 1st, 2013, 07:28 AM

Absolutely good info Sam.

I do have one or two observations about air filters inside the airbox. I discovered that the foam air filters can compress under suction along with producing turbulent air. Sort of what you were wondering about.

The current air filter I have now reduces turbulent air, compression and provide a better laminar flow because of it's construction. It's also allowing the cylinder to fill up better, which is making the engine work a little easier and smoother.

June 27th, 2013, 04:11 PM	#1
quarterliter ninjette.org guru Name: Kevin Location: Madison Join Date: Apr 2013 Motorcycle(s): 2004 Ninja 250 Posts: 465	Shortening intake runners/enlarging opening Anyone tried this? I believe the stock ones are meant for noise reduction and less for performance? Should I shorten the stock length stacks or bore the opening(which in turn deletes the stacks completely)

June 29th, 2013, 07:55 PM	#12
voidrider ninjette.org member Name: Sam Location: Klamath Falls, Oregon Join Date: May 2010 Motorcycle(s): 1996 Kawasaki Ninja 250, 2000 Kawasaki Super Sherpa Posts: 79	Those tubes are actually called Helmholtz Resonators. They actually serve a (albeit minor) purpose. Just for informational purposes... The overall concept is that air is of course a fluid. The valves/piston draw air into the carbs, you can sort of think of each "draw" as a pulse or "blob" of air. Its sort of weird to think about, and it goes into the realms of laminar and non-laminar flow in fluid mechanics, but simply put, if a fluid is traveling smoothly through a pipe or system, and not "bouncing against all the other blobs of air", you get more air through the system. (Its actually more about pressure waves and regions, but the pulse/"blobs" model works). The length and diameter and even the angles of the resonators are "tuned" to help the air move through the carbs and into the engine head with good flow. But its not even that simple. You want laminar flow to get high volume of air into the cylinders, but you want "the right amount" of non-laminar flow downstream of where fuel enters the system to get a good fuel air mix. There are some videos and computer animation that show the atomization of fuel and how the flow moves though the valves and into the cylinders. Overall its a pretty good system, and anymore its getting near to an exact science, but the design engineers usually don't design for "performance", a lot of thought goes into reliability, a "level of of functionality" and probably a half dozen other criteria with all the compromises that comes with that sort of thing. Are they necessary? Obviously not! Its just that a poorly designed system with "bigger pipes" is not necessarily more free flowing. It could have bends and reflection points that actually cause less flow. I have a hard time understanding how the Resonators do much good with the air filter in the way, but its supposed to be "tuned" to the size of the airbox, and the volume of air the engine draws per air intake cycle. I think it would be nice to have a system in a wind tunnel type system with smoke and high speed video to actually make visible the pressure waves in systems, like pods, an airbox with no lid, stock airbox, etc. Then you could do a cross reference of carb adjustments. Following that with dyno tests would be great, and that is pretty close to what the big racing team engine guys are doing between races. From that sort of testing you could pull the data off that applies to your style and type of riding. The system the engineers came up at KHI is what comes stock, its good for most riders under most conditions for most riding styles. Knowing how/why they arrived at their design, and what criteria they used would be valuable knowledge. Since we don't have that, studying the system they arrived at is a good step in knowing what modifications will give the biggest benefit. If you go to a more free flowing exhaust, its does very little good unless you can supply more fluid into the system, and the reverse is also true. If you don't balance the in and the out you will not really get the full advantage of your alterations. Last futzed with by voidrider; June 29th, 2013 at 08:00 PM. Reason: spelling
	1 out of 1 members found this post helpful.

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June 27th, 2013, 06:14 PM	#2
agent of orange ninjette.org member Name: trent Location: halifax canada Join Date: Sep 2012 Motorcycle(s): gsf1200, gsxr750, r6, gpz400, gpx400r, zx6d Posts: 21	you would have to tune the carbs for it. shorter stacks will give you higher peak hp number but you will reduce your low mid range torque. i think thats how it works.

June 27th, 2013, 06:16 PM	#3
agent of orange ninjette.org member Name: trent Location: halifax canada Join Date: Sep 2012 Motorcycle(s): gsf1200, gsxr750, r6, gpz400, gpx400r, zx6d Posts: 21	or you mean the carb to head boots? as the 250 has pretty long ones and the diameter matches the bore of the carbs

June 27th, 2013, 06:48 PM	#4
quarterliter ninjette.org guru Name: Kevin Location: Madison Join Date: Apr 2013 Motorcycle(s): 2004 Ninja 250 Posts: 465	Orange i was talking about the insert that goes into the top of the airbox. The lid sort of thing. I might shorten them up but im just trying to figure out if I want to make the openings bigger b/c the carbs opening is larger than these holes.

June 27th, 2013, 06:59 PM	#6
quarterliter ninjette.org guru Name: Kevin Location: Madison Join Date: Apr 2013 Motorcycle(s): 2004 Ninja 250 Posts: 465	Do you see the curves heading into the runner on the stock one? I want to keep those I think the dimensions were designed to help with flow. I was thinking of boring then out keeping some of those angles but increasing the area of the openings. But i would lose all the runner length as boring it would get rid of them.

June 27th, 2013, 07:02 PM	#7
quarterliter ninjette.org guru Name: Kevin Location: Madison Join Date: Apr 2013 Motorcycle(s): 2004 Ninja 250 Posts: 465	^in the link that Dablue posted

June 27th, 2013, 07:53 PM	#8
choneofakind ninjette.org certified postwhore Name: . Location: . Join Date: Feb 2011 Motorcycle(s): . Posts: Too much. MOTM - Feb '13, Feb '14	I cut those out with good results. The bike really seems to like it. Just remember to shim your needles a tad. Currently, I'm running an open intake lid, full exhaust, and fuel injection. The air still seems to be smooth because it gives consistent performance. I ran the same setup with carbs and got good results as well. Throttle response in the mid-range is a touch better, top end is a touch better, sounds good as well. Not sure how much of this is the intake change vs how much is the jetting change. here's a picture:

June 27th, 2013, 07:57 PM	#9
choneofakind ninjette.org certified postwhore Name: . Location: . Join Date: Feb 2011 Motorcycle(s): . Posts: Too much. MOTM - Feb '13, Feb '14	Just curious here Kevin, have any of your little changes (sanding, etc) actually made any noticeable difference? I honestly thing a clean air filter and a little jetting help would make more difference than sanding the inside of the air box

June 28th, 2013, 06:57 AM	#10
quarterliter ninjette.org guru Name: Kevin Location: Madison Join Date: Apr 2013 Motorcycle(s): 2004 Ninja 250 Posts: 465	I just had the air box off anyways....but regardless haha I do all sorts of little things that I believe add up. I raced another 250 a little while ago and my bike pulled noticibly harder. Granted I am only 135 lbs

June 28th, 2013, 10:04 AM	#11
choneofakind ninjette.org certified postwhore Name: . Location: . Join Date: Feb 2011 Motorcycle(s): . Posts: Too much. MOTM - Feb '13, Feb '14	I'm light also, no worries. Right around 135 without gear on. Go for it with the intake lid! One trick I found was that if you sand the edge you cut, then brush it lightly with the flame from a blowtorch/lighter, then edge melts just a tad, and really cleans up all the plastic burrs/whatever from sanding. Not necessary, but looks a lot better. This goes for any cuts you make to ABS plastic.

June 30th, 2013, 11:06 AM	#13
choneofakind ninjette.org certified postwhore Name: . Location: . Join Date: Feb 2011 Motorcycle(s): . Posts: Too much. MOTM - Feb '13, Feb '14	Good info Sam!! Yes, I knew about the intake resonances and why those tubes are there, but the bike does seem to respond very well with a full exhaust and the intake lid opened. In a perfect system, those resonances can be very helpful. My question is; does opening the intake lid ruin those pressure waves in the air? There is still a solid back, and still a long flow of air for the waves to travel along. It would seem to me like opening the intake lid would not ruin the ability of the pressure waves to bounce back and forth in the air box. It also seems to me like the foamy OE filter would dampen some of those so that it really doesn't matter either way. You talk about laminar flow and getting the correct proportion of dirty air to mix fuel and air; one of our members from Greece with OE FI setup mentioned drilling holes in the air box in opposing corners in order to create a 'swirl' pattern inside the air box. Do you think this would be beneficial to mixing air and fuel consistently?Judging by how much better my fuel injection setup runs with the air box compared to a pod filter, I assume that the air box with the opened intake lid provides more clean air flow than a pod filter. However, I'm also willing to try small things to help that out however I can. I'm asking questions because I'm curious, and I hope to stimulate some conversation from users who know what they're talking about and can help us all learn. Let me know what your thoughts are on this.

June 30th, 2013, 06:09 PM	#15
choneofakind ninjette.org certified postwhore Name: . Location: . Join Date: Feb 2011 Motorcycle(s): . Posts: Too much. MOTM - Feb '13, Feb '14	Sam, that was one awesome post! Thanks for the time and thought you put in on that. I'll be keeping this topic in the back of my mind when I go through Fluids class this year. (Starting my junior year of ME at Ohio Northern University this fall) Hopefully I can pick my prof's brain a little bit on the topic of air boxes and swirling air and air filters. My understanding of this is basically modeled by a slinky being compressed and extended longitudinally; you'll see the 'piling up' and you'll see the 'wave' transfer along the length of the slinky. However, my slinky model only accounts for the 'tube' section of the air box (into the carb/throttle body) and does not really account for the volume of still air in the box, or the effect of the filter on the wave. Once I get to that part, I get kinda lost.

July 1st, 2013, 07:28 AM	#16
DaBlue1 Long Time Rider Name: Blue Location: Charlotte, NC Join Date: Sep 2010 Motorcycle(s): 2009 Kawasaki Ninja 250R Posts: A lot.	Absolutely good info Sam. I do have one or two observations about air filters inside the airbox. I discovered that the foam air filters can compress under suction along with producing turbulent air. Sort of what you were wondering about. The current air filter I have now reduces turbulent air, compression and provide a better laminar flow because of it's construction. It's also allowing the cylinder to fill up better, which is making the engine work a little easier and smoother.