supra5677
Pro
Posts: 1279
|
posted February 07, 2010 12:20 PM
AIR BOX PRESSURE UPDATE
I was able to find a 200 millibar pressure gauge from Ashcroft Gauges. ( 68.9 milibars equals 1 psi.) I didn't want to drill holes in the air box which is why thissmall project has been on hold. I finally found a grommet screw that goes directly into the air box. The gauge has a 1/8 th inch tube that connects to the back of the gauge from the air box entrance. No leaks. Once I mount it to the handle bars I can read the gauge.
At idle when revved it reads between 0-2 millibars. I cut the intake resonators off and sealed it with plexiglass. I'm not sure that will
make a difference but we will see. I know Psycho has done some similar measurements..
Supra
   
|
Shane661
Needs a life
Posts: 11494
|
posted February 08, 2010 02:46 PM
Let us know what the airbox pressure is over ambient...at say 190+ mph. 
|
KZScott
Needs a life
high on speed
Posts: 7235
|
posted February 08, 2010 02:53 PM
what are you trying to accomplish?
____________
01 ZX-12R 8.84 @ 156.3 no bars, DOT tires. Pump Gas, NA.... turbo 8.47 @ 164.
00 ZX-12R 8.62 @ 165.2 no bars, slicks, Pump Gas, 55 shot.... turbo 8.32 @173
00 ZX-12R Fastest NA Kawasaki in the world 1: 222.046 1.5: 226.390 Loring AFB
00 ZX-12R street turbo 1: 227.9 1.5: 234.1 Loring AFB
00 ZX-12R LSR turbo 1: 263.1 1.5: 266.5 Loring AFB Worlds fastest ZX-12R
CMG Racing RCC Turbos
|
supra5677
Pro
Posts: 1279
|
posted February 08, 2010 03:19 PM
Iv'e been reading Kevin Camerson's Sports Bike Performance Handbook. Excellent Reading on Air Box Resonance Frequencies etc.
1. I'm trying to see how much pressure the air box can generate.
2. Using the resonance formula it is possible to move around the power bands.
3. What I'm trying to accomplish is more horsepower and of course go faster!
supra
|
Y2KZX12R
Needs a job
CompetitionCNC.com
Posts: 3762
|
posted February 09, 2010 04:16 AM
Logging at 200+mph I saw about 30 mb of pressure on my 2000 zx12r with all stock ramair system and a 1427cc engine with big valves and stage 2 cnc porting.
____________
Y2KZX12R
CompetitionCNC.com
|
supra5677
Pro
Posts: 1279
|
posted February 09, 2010 04:35 PM
I remember seeing that data, I think on another site. Question.
1 30mb of pressure is horrible. About 7 bhp.
2 Is your box sealed?
|
Shane661
Needs a life
Posts: 11494
|
posted February 09, 2010 04:41 PM
 Edited By: Shane661 on 10 Feb 2010 00:44
Hey Supra...with all due respect....
WTF are you talking about? You are hardly in a position to assess any ram air system. Instead of using a data logger to accurately plot airbox pressure you are using a gauge....because you don't want to drill a hole.
You offer advice such as telling someone to measure airbox volume with Lego pieces.
You sound like a complete idiot. No offense.
|
KZScott
Needs a life
high on speed
Posts: 7235
|
posted February 09, 2010 05:17 PM
this is the guy that thought a zx14 crank would fit the 12r cases...
i stress again supra, there are proven mods out there to get more hp. when you run out of those then try this stuff. you will get more positive results
____________
01 ZX-12R 8.84 @ 156.3 no bars, DOT tires. Pump Gas, NA.... turbo 8.47 @ 164.
00 ZX-12R 8.62 @ 165.2 no bars, slicks, Pump Gas, 55 shot.... turbo 8.32 @173
00 ZX-12R Fastest NA Kawasaki in the world 1: 222.046 1.5: 226.390 Loring AFB
00 ZX-12R street turbo 1: 227.9 1.5: 234.1 Loring AFB
00 ZX-12R LSR turbo 1: 263.1 1.5: 266.5 Loring AFB Worlds fastest ZX-12R
CMG Racing RCC Turbos
|
supra5677
Pro
Posts: 1279
|
posted February 09, 2010 05:28 PM
Ok Shane. I will not take offense. First time Iv'e ever been called an idiot.
|
shiphteey
Needs a job
Posts: 2529
|
posted February 11, 2010 01:38 PM
Supra....what speeds to you plan to log airbox pressure up to? There is an old Sport Rider article on the ZX-9R B model (94-97) where they logged airbox pressure and I think at speeds of 160 or so it was about 9-10 HP gain? Which is inline with what I see when I run the 98 against 929s and literbikes during countless roll-ons.
____________
Gemini Motorcycles
Topping out everything from Ninja 250s to nitrous ZX-14s.
|
Shane661
Needs a life
Posts: 11494
|
posted February 11, 2010 01:57 PM
Edited By: Shane661 on 11 Feb 2010 21:58
quote:
Supra....what speeds to you plan to log airbox pressure up to? There is an old Sport Rider article on the ZX-9R B model (94-97) where they logged airbox pressure and I think at speeds of 160 or so it was about 9-10 HP gain? Which is inline with what I see when I run the 98 against 929s and literbikes during countless roll-ons.
Ali, don't try to play both sides here. 
http://www.bikeland.org/board/viewthread.php?FID=3&TID=52581&set_time=
|
supra5677
Pro
Posts: 1279
|
posted February 12, 2010 12:20 PM
Kawasaki Claims 12.8 bhp in upper speed ranges. I'm planning to log from 40mph to around 175 mph. Kawi claims about 2.3 bhp for every 10 mb of pressure. Y2k's 30 mb is way less than we my buddy logged his zx11 C model.
|
Shane661
Needs a life
Posts: 11494
|
posted February 12, 2010 01:31 PM
quote:
Kawasaki Claims 12.8 bhp in upper speed ranges. I'm planning to log from 40mph to around 175 mph. Kawi claims about 2.3 bhp for every 10 mb of pressure. Y2k's 30 mb is way less than we my buddy logged his zx11 C model.
I wonder why Y2K's bike might have more suction in the box than, say, a 1052cc stock motor?
|
supra5677
Pro
Posts: 1279
|
posted February 12, 2010 04:58 PM
My friend who is a ford test car race driver for a career logged over 68 mb of pressure in his zx11.
|
Shane661
Needs a life
Posts: 11494
|
posted February 12, 2010 05:06 PM
Edited By: Shane661 on 13 Feb 2010 01:08
quote:
My friend who is a ford test car race driver for a career logged over 68 mb of pressure in his zx11.
His stock motor ZX11? Or was it a deep-breathing 1427cc motor spinning at high rpm?
Which motor do you think sucks more air out of the box? Which box is harder to pressurize?
|
shiphteey
Needs a job
Posts: 2529
|
posted February 12, 2010 06:39 PM
Interesting...too bad my airbox pressure readings are skewed by the ol cold dry shot. The one pass I made off spray at Loring I forgot to press RECORD on the LM1...argh....
____________
Gemini Motorcycles
Topping out everything from Ninja 250s to nitrous ZX-14s.
|
KZScott
Needs a life
high on speed
Posts: 7235
|
posted February 12, 2010 07:18 PM
hmmmm 1427cc 12400rpm BMC Race Air Filters Reworked Throttle Bodies w/ Thinned Shafts, Blended Stacks and Manifolds Competition CNC's Stage 2 CNC Porting
Competition CNC's custom Valve Job Kibblewhite 1mm O/S Valves Custom Megacycle Cams .443"/257 Intake .415”/252 Exhaust.......
pressure isnt everything here, flow is. high pressure in the air box could just be a very low hp motor. we all know thats not the case with Jims 220 hp NA-on-pump-gas beast. we do know it flows a hell of a lot of air
____________
01 ZX-12R 8.84 @ 156.3 no bars, DOT tires. Pump Gas, NA.... turbo 8.47 @ 164.
00 ZX-12R 8.62 @ 165.2 no bars, slicks, Pump Gas, 55 shot.... turbo 8.32 @173
00 ZX-12R Fastest NA Kawasaki in the world 1: 222.046 1.5: 226.390 Loring AFB
00 ZX-12R street turbo 1: 227.9 1.5: 234.1 Loring AFB
00 ZX-12R LSR turbo 1: 263.1 1.5: 266.5 Loring AFB Worlds fastest ZX-12R
CMG Racing RCC Turbos
|
Y2KZX12R
Needs a job
CompetitionCNC.com
Posts: 3762
|
posted February 13, 2010 04:51 AM
Edited By: Y2KZX12R on 13 Feb 2010 12:53
I was working with a very qualified friend on this airbox/ram recovery stuff after Loring. We calculated the frontal area of the scoop, speed, engine consumption, etc. looked at all the data from the dyno and the logged runs and cam up with some conclusions.
The system is far from perfect. But the design constraints are what they are and hard to change.
When I have more time I'll post more on this.
Then I put it all on hold because of the thought of switching platforms for this season.
If I dont get a zx14 in the next month or so then I'll continue where we left off and run the zx12r for another season.
But I can tell you that 200mb of airbox pressure isnt accurate.
____________
Y2KZX12R
CompetitionCNC.com
|
supra5677
Pro
Posts: 1279
|
posted February 13, 2010 05:53 PM
Clarification. I have a 200 mb gauge! I would be happy to get 70 mb in the box. 200mb seems impossible.
|
supra5677
Pro
Posts: 1279
|
posted February 13, 2010 06:31 PM
Kirk Cameron claims 10 to 15 percent increase in power if box has correct resonance.The formula is 5300 square root of total area of intake pipe divided by air box volume times length of intake pipe.I'de put some money up to continue this research.
Supra
|
supra5677
Pro
Posts: 1279
|
posted February 13, 2010 06:57 PM
Interesting read:
ntroduction.
Motorcycles have had air boxes holding their air filters for decades. However, in the last couple of decades the purpose of these air boxes has changed quite dramatically.
Originally the air box was just there to keep flying dirt, rain, and bugs from directly hitting the air cleaner. They were simply an attempt to keep the air cleaner a little cleaner a little longer.
In the '70s, the US government started making noise regulations tighter. At some point, the manufacturers realized that the noise from the air intake was part of their problem. They started to look for ways to muffle not only the exhaust, but the intake roar too. Sound waves are pressure pulses in the air. Pistons pull in air on their intake stroke, creating a low pressure pulse in the air box. Then on the compression, power, and exhaust strokes the intake valve is closed and the air box is free to return to atmospheric pressure. These alternating low pressure and normal pressure pulses are sound waves. The manufacturers needed some way to dampen them out.
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.
Part I: Theory.
Here, from first principles we'll develop the theory of how an air box and an inlet tube form a coupled spring- mass system with a resonant frequency.
air box volume = V
inlet pipe = area * length = A * L
Air Mass = 1.25g / 1000 cc
Atmospheric Pressure = 104kg / cm sec2
PV = nkT (Ideal Gas Law)
If the air in the inlet tube moves X cm into the air box, then the volume of air inside the air box changes to:
V' = V + AX
Since Boltzman's constant and the air box volume don't change, that leaves only the temperature and the pressure. The gamma for air is 1.4, so
T' / T = (V' / V)^.4
T' / T = (1 + AX/V)^.4
We'll presume AX/V is small, so (1 + AX/V)^.4 = 1 + .4AX/V
The number of atoms in the air box changes to n' = (1 + AX/V)n. So, the new pressure is:
P'V = (1+AX/V) nk (1+.4AX/V) T
P' = (1 + AX/V) (1 + .4AX/V) P
P' = (1 + 1.4 AX/V) P
Now we can find the spring constant of the air box, K:
Force = Pressure*Area = Kx
Kx = 1.4 AX/V * A * 104 kg cm / sec2
K = AA/V * 146 kg / sec2
The mass of air in the inlet tube is
M = AL * 1.25g / 1000
The resonant frequency w, in radians per second, of a spring-mass system is:
w = sqrt( K/M )
= sqrt( AA/V * 146 kg / sec2 * 1000 / 1.25g AL )
= sqrt( A/VL * 146*1000*1000 / 1.25 sec2 )
= 1000 sqrt( 116.5 A/VL ) / sec
The resonant frequency is w / 2pi, and the resonant rpm is 30 * number of cylinders * f. For a V-twin, rpm = 60 * f.
f = w / 2pi = 160 sqrt( 116.5 A / VL )
resonant rpm = 4775 sqrt( 116.5 A / VL ) (single cylinder)
resonant rpm = 9550 sqrt( 116.5 A / VL ) (V-twin)
resonant rpm = 19100 sqrt( 116.5 A / VL ) (4 cylinder)
Part II. Applications.
Here we'll examine a particular design, and see if we can understand the purpose of the design.
On the Suzuki V-Strom, the air box holds approximately 8 liters, about 8000 ccs. There's an inlet pipe which has a 90 degree bend in it. The two sides, inner and outer, differ in length a bit. We'll use their average, the centerline distance, as the length of the pipe. The pipe opening is about 200 square centimeters, and the length is about 20cm. Fortunately, as all these numbers appear inside a square root, our results will not depend on highly accurate measurements. Of course, if you're designing an air box you would want to be quite precise, but we're just trying to understand an existing design, so if we're off by a few percent it won't really matter. We'll also concern ourselves with the flow through the pipe and see if the mach number of the airflow is low enough to ensure linearity.
At 12,000 rpm, the V-Strom's 1 liter motor is pumping 6,000 liters per minute, 100 liters per second. The V- Strom inlet snorkel has an opening of about 200 cm2. 100 liters per second is a column of air 1000 cm 2 wide by 10 meters long, or 200 cm 2 * 50 meters long, so apparently the peak velocity through the inlet tube is less than 50 meters per second. The speed of sound at sea level is about 340 meters per second, so this is about mach .14.
Whenever air flows past something, like the walls of the inlet snorkel, the air touching the walls will stick to the walls and not flow. The air very close to the stuck air will flow, but sluggishly because the nearby air isn't moving. Thus there will be a region of air right next to the tube walls which does not flow easily. This area is called the Poisson stagnation region, named after the French physicist who first described it mathematically. The faster you try to flow air through the tube, the thicker the stagnation region gets. In a narrow tube at extremely high flow rates, the stagnation regions can grow to pretty much fill the tube and the flow through the tube can get slowed quite dramatically. However, mach .14 is not a very high flow rate. This low peak velocity guarantees the Poisson stagnation region on the tube walls will remain thin, and the tube will be substantially open for free flow. We've satisfied the engineers's prayer "Please, God, let it be linear."
The resonant rpm will be 9550 * sqrt( 116.5 A / VL ) = 9550 * sqrt( 116.5*200 / 8000*20 ) = 9550 * sqrt ( 116.5 / 800 ) = 9550 * .38 = 3650 rpm
This number is consistent with the torque dip in a 10,000 rpm v-twin with valve overlap. Remember, we only estimated the volume of the air box and the length and width of the snorkel, so 3650 rpm is just an estimate and is most likely off by a few hundred rpm. Apparently the Suzuki engineers designed an air box which would resonate at the torque dip, thereby giving essentially frictionless airflow at the rpm where the engine was having the most trouble making torque.
If you decided to make substantial modifications to your engine, like high compression pistons, new cam shafts, and re-mapped ignition and fuel injection, you would very likely change the rpm at which the mid-range torque dip happens. In this case, if you can measure the new rpm on a dyno, you could use this information and our formula to decide on a new snorkel length to change the air box resonance to match the new torque dip.
|
supra5677
Pro
Posts: 1279
|
posted February 13, 2010 07:29 PM
Interesting Reading Part 2
QUOTE:-
Oddly enough, I am pursuing this very topic (design of a resonant airbox) on another forum. I'll let you know if I get any good responses!
Here is from a previous post on this topic
OK, this is regarding my diesel, but just so you know I'm still pondering airboxes and this one is a good example.
Typical helmholtz resonators are a volume (airbox), fed by a duct of certain length and cross section. these 3 things determine the resonant frequency of the airbox. look at an RGV250 and you see a pair of inlet ducts, a few inches in length, that feed the airbox. shortening those ducts raises airbox rez freq. anyhow--
My TLS has a little flapper in the inlet duct, it closes at low rpm. to provide restriction? nooope- read on!
OK, I gave the TLS airbox my best analysis. (sat and stared at it) just how does the flapper affect things? The airbox is a CLASSIC helmholtz resonator, complete with entry duct (that is the tube coming up from the floor) . stock, I figure (flapper open) the duct length is approx 2.4" and area is approx 5 sq in. with a box volume of 550 cu in it resonates at approx 120 Hz.
flapper closed, sectional open area of inlet duct approx 1 sq inch, airbox now resonates at 53 Hz (low end boost)
remove flapper, you lose that variable resonance
shorten the inlet duct to 1" in length, resonance goes up to 184 Hz. cut it off completely and I'm not sure what happens?? This is a very clever bit of work. The TL has a weird double-gulp intake event every other revolution. I'll treat it as a single for simplicity- with flapper closed, the airbox resonates approx 3200 cycles/min, so you'd have a weaker resonance at 1600 rpm and then a stronger resonance at 3200 rpm. once the flapper opens, you have airbox resonance at 7200 cycles/minute -- so you get a weak resonance at 3600 rpm --and a stronger resonance at 7200 rpm.
All these resonators use a box with inlet duct of certain length. it's never just an open hole. There has to be a better way to improve things than cutting everything out of there.
One could apply this to an RG500 airbox- one on each side of the engine- sufficiently large... the use of a flapper could seriously aid low rpm power
Say we want a boost at 3000 rpm, where we have 6000 intake events/min we can shoot for a helping wave every other revolution (3000 cycles/min D 50Hz) treat each side separately- I think one could make an airbox of 400 cu in (0.23 cu ft) on each side. feed this through an inlet duct of sufficient size, - say - 4 sq in (.0278 sq ft) , , with a flapper that blocks it down to 1 sq in (.007 sq ft) . and length of... 3.6" that gives a resonance at 52 Hz. with flapper open, resonance occurs at 104 Hz (6240 cycles/min) and you get a boost in the midrange at 6200. or juggle the inlet tube length to counteract the pre-pipe flat spot anyhow, I'm still working on stuff... but my next effort will have airboxes that work!
So long
Randy
and more from 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, snowmobile 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.
snipped- post was over size limit
BACK TO THE AIRBOX
Any hi-fi enthusiast knows that woofer enclosures work best when the resonant frequency of the enclosure is nicely centred 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 carburettors. 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. Carburettors 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 analysers 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?
The airbox inlet tubes, or 93horns 94, are specifically designed to provide a resonance that can increase the total airflow by up to 10-15%. Removing these can cause the engine to loose power and increase the intake noise.
We're so used to the idea that problems have to be solved with silicon logic that we forget about steel and aluminium solutions. 93Wave 94 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 D 137 revolutions per second, or 137 X 2 D 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 D 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.(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-resonance. 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.
So long
Randy Norian
http://homepage.mac.com/rg500delta/RandysAddiction/
|
wrongway
Pro
Posts: 1078
|
posted February 14, 2010 12:34 PM
quote:
Interesting read:
The air in a box is compressible, so a box is the acoustic analog of a capacitor or spring.
I don't think so ...from http://www.centennialofflight.gov/essay/Dictionary/Compressibility/DI136.htm
quote:
A gaseous fluid such as air, on the other hand, can be either compressible or incompressible. Generally, for theoretical and experimental purposes, gases are assumed to be incompressible when they are moving at low speeds--under approximately 220 miles per hour. The motion of the object traveling through the air at such speed does not affect the density of the air. This assumption has been useful in aerodynamics when studying the behavior of air in relation to airfoils and other objects moving through the air at slower speeds.
However, when aircraft began traveling faster than 220 miles per hour, assumptions regarding the air through which they flew that were true at slower speeds were no longer valid. At high speeds some of the energy of the quickly moving aircraft goes into compressing the fluid (the air) and changing its density.
does that screw up all your calculations ?
Roy
|
Shane661
Needs a life
Posts: 11494
|
posted February 14, 2010 12:41 PM
Edited By: Shane661 on 14 Feb 2010 22:18
quote:
does that screw up all your calculations ?
Roy
What speed is the air traveling at as it enters the airbox??
When you look at the air intake design, you can see that the passages narrow which would presumably increase the air velocity. So, a motorcycle travelling at 200 mph would likely have an intake air velocity moving at a much higher speed, wouldn't it? I truly don't know the answer, but I do know that as the port narrows the velocity must increase in order to deliver an equal amount of total flow.
If there is no air compression, is it even possible to have greater than atmospheric pressure inside the box? I believe that the well designed systems can net .5 psi or more above atmospheric pressure.
On another note, I think we are looking at two distinctly different areas of the intake air system here. One is tuning the airbox for an optimum resonant frequency. The other is designing the intake for maximum pressurization at speed. The whole system has to work as a package. Anyway, that's enough theory for me. 
Shane
|
supra5677
Pro
Posts: 1279
|
posted February 14, 2010 02:19 PM
Ok Mr. Shane:
We appear to be on the same page.
1. Resonance of box
2. Intake system for max pressurization
Goal: To Go Faster!
|
|
|
|
|
HOME
NEW TOPIC