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Discussion Starter · #1 ·
If we ditch the pair plumbing, and move the crankcase breather, is it possible to just run straight pipes from the air cleaners to the throttle bodies? What would be the disadvantages? I think maybe one disadvantage would be no draining of water if it got in there, but besides that?

I'm thinking that some smoothly curved tubes straight to the throttle bodies from the air cleaners might be more laminar.
 

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phaed said:
If we ditch the pair plumbing, and move the crankcase breather, is it possible to just run straight pipes from the air cleaners to the throttle bodies? What would be the disadvantages? I think maybe one disadvantage would be no draining of water if it got in there, but besides that?

I'm thinking that some smoothly curved tubes straight to the throttle bodies from the air cleaners might be more laminar.
I'm sure your stock intake, which is connected to both throttle bodies, is one large cavity with two intake holes, one to the back of each air box. Technically speaking, I believe that when a cylinder is on the intake stroke and the intake valve is open, you are drawing air through both right and left filters simultaneously. If you place two separate intake pipes, one to each throttle body, you are reducing the total volume of air available to the cylinder. A separate intake runner for each filter sounds good but I think it is one of those mods which would have to be proved with some dyno time for a real comparison to be made.
 

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Discussion Starter · #3 ·
I believe that when a cylinder is on the intake stroke and the intake valve is open, you are drawing air through both right and left filters simultaneously
that's a good point.

maybe a 2 into 1 into 2 system that's more smooth (the stock airbox is pretty chaotic) might be beneficial. the way it is stock, the right air filter flows "over" the the left throttle body intake (rear jug), and left filter "over" the right throttle body intake (front jug). if both filter tubes could be spiraled into a circular cavity, it might get some smooth vortex going.
 

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raw_taz said:
I am being told that Volume of Air is going to be the problem with direct velocity stacks.

TAZ
Seems logical that each separate stack would have to have at least the volume of the stock air intake :bigthumbsup: :bigthumbsup: :bigthumbsup:
 

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[from http://www.calsci.com/motorcycleinfo/Airboxes.html]

Resonant Airboxes

Your exhaust mufflers are made of a series of open chambers connected to each other by tubes. The exhaust pressure pulses get caught in the chambers and bounce around in them, then have to leak out relatively slowly through the tubes. The math that governs mufflers can also be applied to air boxes: you need a big chamber to hold a bunch of air, and an inlet tube to let air in at a controlled rate.

The air in a box is compressible, so a box is the acoustic analog of a capacitor or spring. Air has mass - about 1kg / cubic meter, about 2 pounds per cubic yard. In a tube, the air moves back and forth as a slug, as long as the frequency of the movement is small compared to (tube length / speed of sound). So, at low frequencies a tube is a mass term. Since the speed of sound is about 1000 feet per second, a foot long tube is equivalent to 1 khz. 10,000 rpm is 160 pulses per second on a V-Twin, so "low frequency" clearly applies on an air box for any snorkel shorter than about 6 feet long. A wire screen is the acoustic analog of a resistor. It slows air motion, converting the energy into heat. The combination of a box and tube is a system with a resonance. Exactly as a child's swing has a resonant frequency, exactly as a ported speaker enclosure has a resonant frequency, so does your air box.

A system at resonance is nearly perfect - there are small frictional losses in any system, but at resonance these are the only losses. Imagine pushing a child on a swing - it takes very little energy to keep her going at the natural frequency of the swing, just a little push each swing is enough. The only thing slowing her down is air resistance and a little friction in the chains. So at resonance, air flows through a tuned air box almost without resistance. This is as close as we can get to a superconductor of air.

A modern engine with valve overlap will naturally have a dip in the torque at about a third to a half the red line rpm. If the air box is tuned to have minimum resistance to air flow at this rpm, the dip in the torque curve will be partially filled in by the ease of pulling air into the engine.

So, your air box is most likely designed to add horsepower in the mid-range. The air box will have little or no effect on peak hp.

Years ago, before airboxes were designed as resonant systems, it used to be popular to cut additional holes in the air box to allow more air flow for high rpm. This is no longer a good idea. Modern air boxes can flow much more air than the engine will ever use. Modern engines have throttle bodies or carburetors with throats that are typically about 45mm in diameter, about 16 sq.cm in area. The inlet snorkel to a modern air box will be roughly 300 to 800 sq.cm - much larger than the throttle body or carburetor throat. The idea that the snorkel makes for a significant impediment to air flow into the engine is questionable at best. Drilling holes to let in more air is exactly equivalent to drilling holes in your speaker cabinets to let out more sound. Removing the snorkel from your air box is the exact same thing as removing the port in your speakers, the tube that's carefully engineered to have just the right diameter and length to reinforce the bass on your speakers at low frequencies. By altering your air box in any significant fashion, you're most likely going to cost yourself three to five hp in the mid range, and gain nothing measurable at high rpms.
 

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WOW!! Excellent post, very informative for those of us with little or no practical mechanical knowledge, like me. Thanks for the post!!

:bigthumbsup:
 

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Discussion Starter · #7 ·
very cool stuff, thanks for posting jeffw
 

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That's a very interesting set of analogies Jeff -- but I'm not sure that they really apply to this situation.

Some months ago on this Board there was a great link to a video showing a small rice burner car hooked up to a dyno. The guys in the video simply shoved the end of a hair dryer into the air intake, and showed very significant gains in H.P. -- thus, no matter what size the throttle body, if you can generate some "ram air" effect with your air intake, there are going to be some gains, especailly if the extra air is matched to some additional fuel with a Power Commander.

Assuming that the cylinders are simply "sucking" the air/fuel in during their down stroke, your theory(ies) may have more relevance.

Nonetheless, they are going to be sucking a lot more air in at high rpm than they are at low. Your post suggests that if you were sucking air through a straw, and that straw had a constriction in it (throttle body) -- that there is a way to design the portion of the straw leading to the constriction so that it would be "tuned" to optimize flow and a certain flow-rate. Although this is probably true -- it is also true that if you suck harder than that SPECIF flow rate, you are going to quickly be out of that "optimal" flow rate range. Thus "tuning" an air box would be limitied to a narrow (and specific) rpm range. Above and below that range, you're going to be de-tuned.

The question at hand is whether you gain more eliminating turbulence and other factors (lenght of tube, etc.) than you gain by being "tuned" at that specifc flow rate.

To me this is exactly the type of question that can be best resolved by testing under different conditions. Lamosnter's pre- and post- Big Air dyno runs suggest that the gains outweigh the losses when you open up the intake with the air boxes ON -- the same would have to be done with the air boxes on and off to see what actually happens (unless you have a PhD in physicis) -- and even then I'm not sure.
 

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That post (from the site that I listed) was talking about a Suzuki V-Strom (1000CC v-twin), so I really think it does somewhat apply to the M109.
 

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tomph1 said:
  That's a very interesting set of analogies Jeff -- but I'm not sure that they really apply to this situation.Â

   Some months ago on this Board there was a great link to a video showing a small rice burner car hooked up to a dyno. The guys in the video simply shoved the end of a hair dryer into the air intake, and showed very significant gains in H.P. -- thus, no matter what size the throttle body, if you can generate some "ram air" effect with your air intake, there are going to be some gains, especailly if the extra air is matched to some additional fuel with a Power Commander.

  Assuming that the cylinders are simply "sucking" the air/fuel in during their down stroke, your theory(ies) may have more relevance.Â

  Nonetheless, they are going to be sucking a lot more air in at high rpm than they are at low.  Your post suggests that if you were sucking air through a straw, and that straw had a constriction in it (throttle body) -- that there is a way to design the portion of the straw leading to the constriction so that it would be "tuned" to optimize flow and a certain flow-rate.  Although this is probably true -- it is also true that if you suck harder than that SPECIF flow rate, you are going to quickly be out of that "optimal" flow rate range. Thus "tuning" an air box would be limitied to a narrow (and specific) rpm range. Above and below that range, you're going to be de-tuned.Â

  The question at hand is whether you gain more eliminating turbulence and other factors (lenght of tube, etc.) than you gain by being "tuned" at that specifc flow rate.

  To me this is exactly the type of question that can be best resolved by testing under different conditions. Lamosnter's pre- and post- Big Air dyno runs suggest that the gains outweigh the losses when you open up the intake with the air boxes ON -- the same would have to be done with the air boxes on and off to see what actually happens (unless you have a PhD in physicis) -- and even then I'm not sure.

 Â
I have no PhD in Physics but would like to offer this observation. Under normal aspiration the maxim air intake to a cylinder would never exceed the volume of the cylinder itself unless the entering air was pressurized by either a turbo or blower. If your plenum is equal in volume to the volume of the piston cylinder ( bore x stroke ) then you would have a 1 to 1 ratio. Regardless of engine speed the cylinder fills at the same volume on each intake stroke. Engine speed will increase the rate at which the cylinder fills but would not increase the volume per stroke. Ramming air with a hair dryer would technically provide positive boost/pressure to "charge"the intake air and have the effect of a low grade turbo/blower. There is a assumption that pointing air filters to the front of a cycle has a "ram air" effect on the intake system. That my be more myth than fact. It would be interesting to know how many PSI positive pressure was created by the blow dryer.
 

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Discussion Starter · #11 ·

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Discussion Starter · #12 ·
just a quick calculation for our bike:

1.783 L * ( 1000 rpm / 2 ) / 60 sec = 14.68 L/sec = 3.88 gal/sec

1.783 L * ( 7500 rpm / 2 ) / 60 sec = 111.44 L/sec = 29.42 gal/sec

*the division by 2 is necessary for 4 strokes because it only consumes air on every other revolution

ideally, our bike wants to consume 3.88 gallons per second of air at idle speeds. this increases to 29.42 gal/sec at redline.

i had no idea it required this much airflow. fluid dynamics and sound wave resonance aside, it's easy to see why the intake system is so important now. it's also easy to see why those puny stock intakes hinder this.

p.s. i'd appreciate it if someone else would check my math
 

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The air box acts as a storage place for air. The only reason to get rid of it would be to run velocity stacks with no sort of plumbing on the throttle bodies.
 

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kat here is my 2 cents not worth much. the more air you cram in to it the more power (blowers) pc3 = more power so yes if you took off the stock air box and put on a velocity stack style intake yep more horse power. :bigthumbsup: imo
 

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Navy Guy said:
kat here is my 2 cents not worth much. the more air you cram in to it the more power (blowers) pc3 = more power so yes if you took off the stock air box and put on a velocity stack style intake yep more horse power. :bigthumbsup: imo
That's what I said ;) :clap2:
 

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I have taken the air box off of a few bikes as new as 99' that had carbs but the airbox was not ram aired. by taking the box off and running 4 K & N pod filters right on the back of the carb and rejetting it ran much better than stock, no driveability problems or holes in the midrange provided it was jetted properly. that was on a carb'd bike so a FI bike should be even better given the tuning potential. this air box on the 109 looks like it was made due to compromises on space or lack of it and looks to have little tuning value.
 

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raw_taz said:
Go to the busa boards, there are guys making better air boxes, and there are guys running velocity stacks only for track, but the two present totally different benefits and issues.

JR has made some mod's on his that give some HP 1 or 2, but would make must 109r's fill there pants. Meaning bring on that 120lbs of torque right now.

Oh yeah and where are you going to put the 3 sensors for the FI.

Good luck, keep us posted how that works out for you, be sure to post some results, track or dyno. Butt dyno ain't going to cut it.
there are always ways to build a better mousetrap! I know you can take off the secondary butterfly's too (sorry JR) but ever looked at those under tank airboxes that really flow? they are huge, another reason buell and the V-Rod have fake tanks on top. the main thing to realise here is that tiny little air box for this size motor was not contructed for performance. out.
 

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raw_taz said:
From my earlier post

"In theory if the air box was larger we could see more HP if we can make it breathe better, better exhausts, less restrictive heads, bigger valves. It has been explained to me that unless we do all of these things that we are only going to see marginal gains at best and would not be worth the effort."

1 or 2 horsepower unless you spend 5 grand or so.
Not true!!!
 

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raw_taz said:
From my earlier post

"In theory if the air box was larger we could see more HP if we can make it breathe better, better exhausts, less restrictive heads, bigger valves. It has been explained to me that unless we do all of these things that we are only going to see marginal gains at best and would not be worth the effort."

1 or 2 horsepower unless you spend 5 grand or so.
since no one has tested this theory we won't know unless we do! Bikes differ on how they respond to changes in intake and exhaust. just one look at the puny little box on this thing makes you thing of a sumo wrestler trying to breath through infant lungs. :D
 

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One thing I want to try is to block off one off the airfilters on the dyno and see if I drop hp. After reading Jeff's post I'm really curious of what the results will be.
 
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