RLoibl Posted February 21 Share Posted February 21 Hey sports fans, dont know if this topic has been discussed yet, or how I found out if it has....😖😖😖. Looking to buy a K&N air filter, is there any DIY mods to the air box that will improve airflow? Thanks, Ron Quote Link to comment Share on other sites More sharing options...
Member Contributer Thumbs Posted February 21 Member Contributer Share Posted February 21 In a word ……No 1 Quote Link to comment Share on other sites More sharing options...
Member Contributer Mohawk Posted February 21 Member Contributer Share Posted February 21 Ignore previous. Yes there is search Big Airbox mod 👍 Quote Link to comment Share on other sites More sharing options...
RLoibl Posted February 22 Author Share Posted February 22 Couldbnt find Big Airbox Mod anywhere Quote Link to comment Share on other sites More sharing options...
Member Contributer Tirso Posted February 22 Member Contributer Share Posted February 22 Quote Link to comment Share on other sites More sharing options...
Member Contributer BusyLittleShop Posted February 22 Member Contributer Share Posted February 22 Understanding how an air box works and the reasons why a stock box is a safer bet... 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 fuel injected Honda 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! My friend Stephen called long distance from England because he just installed a $900.00 HRC air box on his RC45 and saw 120HP on the dyno... mmmmm... together we wondered if the stock box be modified??? We found that stock RC45 throttle bodies are 46mm but the air box was restricted to 40mm... no problem... I'll bore the air box out to 47mm on the milling machine... I drew up plans for 47mm bell mouth based on the stock 40mm bell mouths and purchased a block of black Delrin... I'm not happy doing repetitious work but I labored long hours to machine 4 each bell mouths with my best accuracy... Don't you love when a plan comes together especially if it turns out perfect??? Now I had an unrestricted air box with my own 47mm bell mouths... it was the best I could do to replicate HRC $900.00 air box... not to mention I wanted to keep my home made K&N filter... Time to put the Mod to the test on the dyno... this is Dave at Chandelle Motorsports... No joy... I lost 1.8HP on the dyno... so bigger is not better in this case... a whole week worth of work shot down in flames... it seems Honda got the intake velocity right for a stock pipe after all... air boxes are like tuned instruments... alter the holes and the tune just makes sour notes and power suffers... Mr.RC45 fueling is not the problem... my air box will remain stock because our air box works like a finely tuned instrument... any wild ass guess mod disrupts this highly engineered resonant to where to you're producing nothing but sour notes... The airbox inlet tubes, or “horns”, are specifically designed to provide a resonance that can increase the total airflow by up to 10-15%. Second guessing these can cause the engine to loose power and increase the intake noise as in my case... RC45's stock intake horns are there for homologation purposes only and do not directly feed into the airbox only the HRC intakes feed ram air into the airbox... 2 2 Quote Link to comment Share on other sites More sharing options...
Member Contributer BusyLittleShop Posted February 23 Member Contributer Share Posted February 23 On 2/21/2024 at 7:27 AM, RLoibl said: Looking to buy a K&N air filter, Hiya Ron... the orange BMC will pass more air than a K&N... but you might need to remap the ECU... K&N are designed to pass just as much air as the stock paper and thus no remapping... Quote Link to comment Share on other sites More sharing options...
Member Contributer Wald Posted February 23 Member Contributer Share Posted February 23 For those interested, Formula one teams did a lot of experimentation with velocity stacks in the 60ties. It was called air resonance charging if I remember correctly. The idea behind was that the air in a long stack with certain conical profile and diameter to length relation could be accelerated in the intake by resonance. There were even books in the engineering section of my school about it. I played with this many moons ago on my first underpowered car and limited funds. These were cool times 2 Quote Link to comment Share on other sites More sharing options...
Member Contributer Mohawk Posted February 23 Member Contributer Share Posted February 23 Yep they did & that is where the Yoshi-stacks & my big airbox mod came from. As Larry explains so well, components have to match in the induction & exhaust systems or the harmonics won't work. Quote Link to comment Share on other sites More sharing options...
Member Contributer boOZZIE Posted February 24 Member Contributer Share Posted February 24 On 2/22/2024 at 2:27 AM, RLoibl said: Hey sports fans, dont know if this topic has been discussed yet, or how I found out if it has....😖😖😖. Looking to buy a K&N air filter, is there any DIY mods to the air box that will improve airflow? Thanks, Ron Be aware that there are 2 different K&N airfilters, the small 1 pictured above and 1 identical to the BMC above Quote Link to comment Share on other sites More sharing options...
Member Contributer tsmitty Posted February 24 Member Contributer Share Posted February 24 @BusyLittleShop nice lathe work. Quote Link to comment Share on other sites More sharing options...
VFR750F3 Posted February 24 Share Posted February 24 I went with the Pipercross. Easier to clean and oil in my opinion. Quote Link to comment Share on other sites More sharing options...
VFR750F3 Posted February 26 Share Posted February 26 I am not sure why everyone is so worried about the size and filtration of their air filters. My modified RC51 uses a tiny foam air filer which was also used on other aftermarket airboxes. Quote Link to comment Share on other sites More sharing options...
Member Contributer bmart Posted February 26 Member Contributer Share Posted February 26 33 minutes ago, VFR750F3 said: I am not sure why everyone is so worried about the size and filtration of their air filters. What do you mean? Quote Link to comment Share on other sites More sharing options...
VFR750F3 Posted February 26 Share Posted February 26 Some k&n filter area is smaller Quote Link to comment Share on other sites More sharing options...
RLoibl Posted February 27 Author Share Posted February 27 On 2/22/2024 at 5:43 PM, BusyLittleShop said: Understanding how an air box works and the reasons why a stock box is a safer bet... 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 fuel injected Honda 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! My friend Stephen called long distance from England because he just installed a $900.00 HRC air box on his RC45 and saw 120HP on the dyno... mmmmm... together we wondered if the stock box be modified??? We found that stock RC45 throttle bodies are 46mm but the air box was restricted to 40mm... no problem... I'll bore the air box out to 47mm on the milling machine... I drew up plans for 47mm bell mouth based on the stock 40mm bell mouths and purchased a block of black Delrin... I'm not happy doing repetitious work but I labored long hours to machine 4 each bell mouths with my best accuracy... Don't you love when a plan comes together especially if it turns out perfect??? Now I had an unrestricted air box with my own 47mm bell mouths... it was the best I could do to replicate HRC $900.00 air box... not to mention I wanted to keep my home made K&N filter... Time to put the Mod to the test on the dyno... this is Dave at Chandelle Motorsports... No joy... I lost 1.8HP on the dyno... so bigger is not better in this case... a whole week worth of work shot down in flames... it seems Honda got the intake velocity right for a stock pipe after all... air boxes are like tuned instruments... alter the holes and the tune just makes sour notes and power suffers... Mr.RC45 fueling is not the problem... my air box will remain stock because our air box works like a finely tuned instrument... any wild ass guess mod disrupts this highly engineered resonant to where to you're producing nothing but sour notes... The airbox inlet tubes, or “horns”, are specifically designed to provide a resonance that can increase the total airflow by up to 10-15%. Second guessing these can cause the engine to loose power and increase the intake noise as in my case... RC45's stock intake horns are there for homologation purposes only and do not directly feed into the airbox only the HRC intakes feed ram air into the airbox... Quote Link to comment Share on other sites More sharing options...
RLoibl Posted February 27 Author Share Posted February 27 Wow, my brain hurts after that!.....lol. great info. I will either get a K&N, or just replace with stock filter. Cheers, Ron Quote Link to comment Share on other sites More sharing options...
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