If this is true, it would seem to totally negate the logic of buying aftermarket air filters :dunno_white:
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
Not sure where you copied that from, but I do not agree. Air boxes on any vehicle I've yet been around are designed for nothing but shielding the filter element and cutting down on noise. I understand the logic and application of a "surge tank" or "volume tank" for engine inlets quite well. The fact of the matter is; the air box on basically any modern vehicle has not had extensive fluid dynamic analysis. It is not designed to improve inlet velocity for low/midrange power. If you don't believe me, look at nearly any dyno chart comparing airbox vs. no airbox on a car, motorycle, moped, etc.
Modern air boxes generally *can not* flow "as much air as the engine requires". At least not any that I've yet seen. That article has some seriously weak logic...
-Turd.
You need to post the source of the article.
Look at a dyno chart of a GS with an airbox and then one with a lunch box along with an appropiate exhaust. Tuned correctly, there is no comparison.
Take the TLR. Removing the air box increases midrange power. The ram air is not effective until above something like 100mph, where it effectively increases hp.
Also, the GS design is from the 70's.
Before this gets out of hand, I just want everyone to know that I also believe the "science" supporting this article is flimsy at best, but I thought that this crowd would find it as ironic and/or silly as I do. :cookoo:
The link of this profundity of info is as follow:http://motorcycleinfo.calsci.com/Airboxes.html
Quote from: ambisinister on May 09, 2007, 09:51:40 AM
Before this gets out of hand, I just want everyone to know that I also believe the "science" supporting this article is flimsy at best, but I thought that this crowd would find it as ironic and/or silly as I do. :cookoo:
Well, its not
horrible logic, its just a bit ill applied. I appreciate you posting this up, its fun to read things like this and decide if they have any merit.
-Turd.
Quote from: dgyver on May 09, 2007, 09:32:07 AM
Take the TLR. Removing the air box increases midrange power. The ram air is not effective until above something like 100mph, where it effectively increases hp.
Well, and even the "ram air" effect is a huge source of debate. I still feel that at even 100 mph the effects are very minimal. The main benefit to such a system is a cooler, denser charge.
Quote from: dgyver on May 09, 2007, 09:32:07 AM
Also, the GS design is from the 70's.
But the air box is a product of the 80's I would assume. Still, I'm sure no more than a few hours were spent in planning out its design. The GS air box is a huge restriction all across the power band.
-Turd.
T78
Just look at a race bike... I don't mean some jim-bob racer, I mean PRO race bikes.
They start with a stock "off the shelf" bike....... If that bike was engineered for max performance, or even only the airbox, then why would PRO racers modify them? They have access to Dynos, computers, tracks, and every other advantage you can think of.
I can't argue with the engineering... But, I can point at a racer. :dunno_white:
Yeah, dynos don't (generally) lie, the affect f removing the airbox has been proven over and over again. If this article had concrete evidence such as a head-to-head comparison of airbox vs. open intake filter in a graph I would hesitantly believe it. But Dgyver is also correct, even if it were true, the GS500 is based on the GS450 of yesteryear, before major emissions regulations.
Good post though, opens up for debate.
does anyone have a before-and-after dyno comparison for with and without the airbox? I'd love to see where the gains are... (this is not scepticism, this is genuine curiousity)
Quote from: thirdman on May 10, 2007, 11:08:48 AM
does anyone have a before-and-after dyno comparison for with and without the airbox? I'd love to see where the gains are... (this is not scepticism, this is genuine curiousity)
We are deafened by the silence. :icon_razz: Everyone's expressing an opinion but no one's bringing proof, so take it with a grain.
For example, recent conventional wisdom making the rounds here is that the airbox is more restrictive than the exhaust. How would anybody know that? :icon_confused:
I'm pretty sure AlphaFire had a dyno done with the lunchbox isntalled. I haven't had time to search, it should be around here somewhere.
Cheers,
J
the argument can work both ways as the bike manufactures have to make the bike pass regulations for pollution regs etc they will always err on the side of less power or noise for the street but if you look at say a new R1 with its adjustable air trumpets I would guess that would make the filter a little useless but for an old aircooled motor like the GS the airbox would restrict due to pollution and noise regs as they are old designs that dont benefit from modern materials and designs to make them perform quietly and with lower emmissions and plus engineers won't put in to much design effort on a cheap bike a guess thats one of the reasons we have a balance shaft in the motor.
[34
Quote from: Wrecent_Wryder on May 10, 2007, 03:57:16 PM
Quote from: Gisser on May 10, 2007, 01:52:30 PM
We are deafened by the silence. :icon_razz: Everyone's expressing an opinion but no one's bringing proof, so take it with a grain.
For example, recent conventional wisdom making the rounds here is that the airbox is more restrictive than the exhaust. How would anybody know that? :icon_confused:
Yeah, well... could be that those who have done both can easily FEEL the difference. Of course, some won't accept that, too subjective...
Right. And in your case you aren't differentiating between richer than stock jetting and the addition of the Lunchbox. You assume that what you FEEL is better breathing rather than simply richer mixture in the EPA strangle-zone.
Quote from: Wrecent_Wryder on May 10, 2007, 03:57:16 PMCould be because those actually doing it have noticed, over and over again, that exhaust changes require minor rejetting changes, and intake changes major. But, of course, some won't accept that either. Doesn't matter how many people have done it and agree, of course, they could ALL just be deceiving themselves...
Correct. They are ignorant of the effect that atmospheric pressure has on the ability of the intake pulse to draw fuel through the mainjet at a given needle position when the main air corrector kicks in. They believe the resulting imbalance to the air/fuel ratio to mean that the engine is
breathing more air instead of the flipside that the intake is
drawing less fuel.
Quote from: Wrecent_Wryder on May 10, 2007, 03:57:16 PMAnd, of course, if someone DID the dyno thing, it would have to be the same bike, the same dyno, carefully controlled conditions, no other changes, reverse each change before applying the next.... and if all else fails, the naysayers can always claim it's a "statistically insignificant sample" or a "probable anomaly".
Have it your way. Here's Alfa's claimed dyno result for the K&N Lunchbox (no pipe): 41.7HP
Here's the official GStwin dyno result for the V&H pipe (airbox intact): 43.2HP. http://www.gstwin.com/dyno_run.htm (http://www.gstwin.com/dyno_run.htm)
Pipe wins. :icon_razz: And with a tiny 122 MJ at that. ;) Is it beginning to sink in?
Now I may be reaching but more HP would mean better breathing and less restriction, no? Of course, this doesn't speak to acceleration beneath peak and that's why the request for the charts.
Quote from: Wrecent_Wryder on May 10, 2007, 03:57:16 PMYou know what? Some people are just never going to be persuaded... and there's absolutely no payoff in trying. They can sit and yell "PROVE to me the Earth is round!", and then get all smug and dismissive when nobody wants to bother, as if that proved their case.
Are we having fun, yet? :laugh:
Quote from: Gisser on May 10, 2007, 07:18:26 PM
Correct. They are ignorant of the effect that atmospheric pressure has on the ability of the intake pulse to draw fuel through the mainjet at a given needle position when the main air corrector kicks in. They believe the resulting imbalance to the air/fuel ratio to mean that the engine is breathing more air instead of the flipside that the intake is drawing less fuel.
Brilliant! Thank you for saying that; I was pondering that exact point, but could not decide how to phrase it.
I just love introducing a topic that I know will cause lively discussion/debate. It's always entertaining. :laugh:
Since I posted this I thought I would also add my two cents since everyone else has already.
Original airbox and exhaust designs on motorcycles (or cars, for that matter) also have to take into account durability issues as well as sound, emissions, ease, and expense of part manufacture,as well as speed of assembly at plant to make it cost effective to build. That's why "works" bikes or professional race bikes are modified so heavily.
We all know that the more horsepower you get out if a given engine inversly affects the durability. So I think we can all cry :bs: on this particular topic. ;)