What Is The Secret Importance Of An Intake Airbox?
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- เผยแพร่เมื่อ 31 ก.ค. 2024
- Think of a motorcycle airbox as a glorified beer bottle. We’ve all blown across the mouth of a bottle and heard the “whoooo” of bottle resonance. If the volume of the airbox and the mass of the air in the intakes are correctly chosen, the box will hum like a beer bottle-and boost engine torque.
If you have ever had the gas tank off your late-model sportbike, you will notice that the front of the fuel tank doesn’t hold fuel; it holds an airbox. In the old days, when you bought a new bike, it had an air-filter case attached to feed the carburetors or the fuel-injection intakes. All the sharp, young guys would immediately rip off the filter case and replace it with four sock filters. Reduced airflow resistance. Much better performance.
One day in the late 1980s, they began to rip off the airboxes of their new bikes and their engines fell on their faces. They lost a bunch of performance. “This can’t be happening! Putting on sock filters always worked before.” But it turns out the industry found a way to boost performance by making what is known as a resonant airbox.
We have all in an idle moment blown across the mouth of a beer bottle and heard the "whoooo" of the bottle resonance. As air goes across the mouth of the bottle, it creates a low pressure, which causes air to flow up. That deflects the air away from the mouth of the bottle. Then the air goes back in, the airflow from your mouth goes back across, and the cycle repeats, rapidly fluttering and producing that deep tone. The compressible air in the bottle is acting as a spring, and the slug of air in the neck of the bottle is the mass that vibrates against that spring.
This intake airbox from a Honda CBR600RR is just a glorified beer bottle. Instead of the engine blowing across the mouth of it, its four throttle bodies are sucking from the box, pulling its pressure down. Air rushes in through the ducts in the fairing to fill up that low pressure. The next cylinder sucks the bottle pressure down and more air rushes in and restores the pressure. If the volume of the box and the mass of the air in the intake pipes are correctly chosen, the box will hum like the beer bottle.
The trick is to get your engine to draw air from the box when the pressure is up and then the box refills when the pressure is down. And that is why ripping the airboxes off and putting on old-time sock filters resulted in a reduction in performance. In a specific zone of rpm, a resonant airbox can boost your engine’s torque by 10 percent. That’s worth having!
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You've done it again Kevin, explained why something I knew worked, works. Thank you for keeping engineering interesting.
That clears up a lot of questions.... excellent video!!!!
thanks for that explanation, i WAS going to remove my airbox on my motorcycle THINKING it would give better airflow and torq. boy was i wrong 🤣
Wow, Kevin Cameron speaks! I didn't know you were here. You are the best!
great explaination thank you for sharing your wisdom. this is what youtube is about!
Fantastic explanation! Thanks
Very well explained , thanks
Thank you, great explanation
So, like an expansion chamber, but on the intake side of the engine!
Always good.
Tq sir..
Love this man...¡¡¡¡¡¡¡¡
does the size of the gearings affect the speed of a motor bike?
Kevin, a few of those hand movements would be dangerous in parts of the world! Silliness aside, another simple & brilliant explanation of what’s important to understand- thanks!
This comment needs more recognition!
After watching this video, I'm not ready to take the test on the theory of resonant airboxes. I heard Mr. Cameron say "beer bottles," and then got lost. We excite an oscillatory mode if we blow the right way? I think a sketch or two on a blackboard might help. Just a suggestion. I do wonder if Mr. Cameron ever washes his hands. Cycle World should run a Cameron hands photographic retrospective, maybe titled "50 years of dirty fingers".
Tell us about the Cycle World staffer who pulled the O2 sensor from a test bike and was puzzled why the performance suffered
Is this also the case with dirtbike air boxes? The only performance modification I’ve seen to dirtbike airboxes over the years is having more holes drilled in them for more air flow. I’m really curious if this idea could be better utilized in the motocross world?
how about single cylinder
10% more torque
Wow 😮
Would you rather have 10% less?
I see people mod mt09 by cutting off the snorkel. I assume the snorkel is to divert water away from the filter. When I do a K&N Filter and Dynojet pc3 tune on my 2019 Tracer 900 GT, should I cut the snorkel or not?
Did u do it?
I put a cone filter on my truck. The results were worse. Sounded good but bad performance. I put the stock box and filter back in.
I wish I've been a woman so I could marry you...
so much knowledge & experience you share and the best thing about them is THE WAY you transfer them to your audience...as always wish the best for you Kevin, keep these videos coming :]
Weird.
@@cryalowicki agree..super duper weird..
It's ok men can marry men now
Dyno testing on my bike says this is mostly true, but there are some larger pod filters that improve horsepower and torque from the bottom to the top.
What pod filters have you tried??
I'm contemplating UniFilter pods with the urethane end cap for my old GS
A T - K&N only added a little horsepower at top end compared to stock air box but was worse in normal running rpm and speed. Tried some pod screens which was worse than stock everywhere Sprint pod filters which were larger added a few horsepower from bottom to top and did the same for torque. I would recommend baselining your bike on dyno then trying a few type of pod filters while bike is still on dyno. EFI bikes with power commanders make it easier to adjust the air fuel mixtures while they are still on the dyno. For bikes with carbs it takes a little more time. The dyno is useful to keep the motor properly fueled throughout the rpm range.
Kevin would be the one guy who wouldn't need a dyno, but there is one of him.
Herr Helmholtz approves!
My Roadstar Warrior has two airboxes. A 1670cc Twin takes big breaths.
So basically, a couple bottle of coke to replace my airbox and I'd get more power? Right, Kevin?
10% torque? Isn't torque a constant value in all engines? I mean, you can't "add torque" to an engine since this is defined by the length of its pieces. Is this right?
You actually can add torque. That's what a supercharger or a turbo does. And that's what a properly sized and turned airbox does also, just as Kevin explains in the video.
What happens to that torque arm when you double the force pushing on it...
My SV1000S looks like it has a huge gastank. Its almost ALL airbox!
@Michael
Thanks for the input. My '03 has run rich from the factory. The higher the rpm the richer it gets. D&D pipes, ignition advancer, and K&N filter have all helped it run better everywhere now. I am glad I didn't do a Power Commander, I have been seeing the 3's causing poor or no running lately on older units.
@Michael
Thanks again. Lambda sensor is wideband O2 sensor? Mine definitely does not have that. It is my understanding the ECU stock won't do that. I get between 45 and 55 mph and fueling has been good since the aforementioned mods. "The Factory" brand ignition advancer (4°) did the most but I love the pipes too. I don't live near anyone with the capability to reflash or program ECUs. I literally live in the middle of nowhere! Regards from Mena, Arkansas.
@Michael
If I get froggy on her I can still get down to high 30mpg. The engine runs fine. I wish the first 3 gears were closer together, the top 3 farther apart. I can only get in to third on a 1000' drag strip. Only does 150 mph on long straights (true, not indicated). My 1000' times have been 9.12 seconds at around 129mph.
@Michael
At 48 I have had my own health issues mainly caused by aviation chemicals. I am glad to say right now I am healthy. I am sorry you are not. Keep up the good fight. Sometimes I only need a good bit of crazy speed and a nice hilly, curvy road to feel better. Fortunately I live at the base of a hill just like that! No cameras here. They can barely afford fuel for the deputies! Blokes from your area ride in a way I only could have until my 30s. After that reality sets in. That's why I ride SV1000S instead of a GSXR1000 or ZX10! Thanks for the conversation. I like this one. If you ever get over here we should meet and ride. If I get back over there I will look you up somehow.
Depends on the bike. My 1988 Honda Nt650 had the tiniest airbox coupled to no more than a 2 inch air opening. Basically no air could get in.
Resonnant air boxes came along after the NT came along.
Samsonite forever! hahaha
Samsonite forever!.... or until a better-looking design comes out, the manufacturers must believe these boxes look awesome, but they don't!
Why is he out of breath? It makes me feel so uncomfortable. Probably running back and forth to his camera, not knowing that he can edit the footage later on.
are you saying that there is no point of using a short intake ram on modern bikes???