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Please don't laugh, I've been a musician my whole life, never a mechanic. I'm learning a lot being a part of this forum, however, I keep reading people saying they have an "open airbox". First off, what does an airbox do, and second, what does it mean/ do to be open? Also, what is a K & N filter and why is it so good? Please be kind to my ignorance...
 

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An airbox for a motorcycle is designed to work with the resonant frequency of the air being sucked into the engine through the carburetors or fuel injection throttle bodies so that the engine will have a smooth powerband. Without an airbox, the engine might make more power at a particular engine speed, like 8000 rpms, but be weaker at some other speed, like 5000 rpms. The original airbox on the Monster has the additional duty of reducing the intake noise to pass federal noise laws.

With the carbureted Monsters, at least, a few more horsepower is available by removing the rubber snorkels in the airbox to let more air flow through at higher engine speeds. This makes more noise when the throttle is open and requires changing the jetting of the carburetors to provide a richer mixture so that the engine produces optimal power. You can get even a little more airflow by cutting open the whole top of the airbox, which we then call an "open airbox".

As for the K & N filter, it is a different air filter that is supposed to let more air through. You can also clean it yourself so that you don't have to buy new air filters every few thousand miles. It's not the only aftermarket air filter; I had a foam Uni-Filter on my Monster. Some people claim that the stock Ducati paper air filter actually flows more air than a K & N filter, but I've never seen any scientific proof either way.

I would recommend getting a copy of Sportbike Performance Handbook by Kevin Cameron, which explains how things like airboxes work, as well as all other parts of a Motorcycle. It's an excellent way to get a good Motorcycle Education.
 

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Thanks Scott, that's very helpful. I figure the only way I'll learn is to ask. I'll definetely look into that book, I want to be able to work on my own bike if need be.
My bike is a '03 620 with no mods. It's completely stock. What benefit would I have from opening my airbox or changing filters? Can I truly expect more noise (a plus ;D) and/or more horsepower?
 

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Yes with an open air box you could expect more hp as well as more noise. Both of those elements are great. The great thing about the "open air box" is that you hear the engine howling out of the air intakes. Here are some ways the air box can be "open"
1. Lift your gas tank and you will see this plastic box with two trumpets portruding from the top. You may remove those.
2. This plastic box's top is held on by clips. If you un snap the clips the top of the box will come off and inside you will find your air filter. You may cut out the middle part of the airbox leaving only the bottom of the lid so that you may fasten the lid back to secure the air filter.
3. You can totally remove this lid and just have the air filter totally exposed. This is the way I ran my bike. I thought it worked very well. Some members have some reservations about doing it this way due to water being able to enter the air box, though I never had any problem with this, AND the bottom of the airbox has a collector and a drain just in case water got in there. Though not very good, here is a picture of my air filter taken from the right side of the bike looking toward the front of the bike.

4. The most advanced way to do this option, which most do not take to, nor helps that much over a true exposed air filter is to delete the whole air box and mount air filters right to your intake mechanism (carb/throttle body) I just did this mod today, and it is mainly for looks, but here it is anyway.


As you go down the list of suggestions, the "potential" for more horsepower increases as each suggestion suggests a way to let more air into the engine. The more air a engine can receive the more power potential it has to make.

The best thing about the "open air box" is that each owner can do as he pleases and will be happy with the results. If you don't want to take your air box lid all the way off, then don't just cut the lid, or whatever, its your bike you decide how you want to modify it.

One last thing is engines need to key ingredients: Air and Fuel, so if you increase one of the two ingredients you need to also increase the latter as to keep them in equilibrium.

-Patrick
 
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Don't forget you will need somewhere for all that "extra" air to go. ie... a more free flowing exhaust!! Depending on what you want to spend, Total System=$$$$, Slip-Ons=$$, Strati=$, Or core your own=FREE. It isn't "necessary", but it does complete the package. And **** if you have more air you will need more fuel so now you are talking ECU upgrade, or ECU tweeked by your dealer, PowerCommander, Or multiple other fuel management systems. Just face it you have been bitten by the MOD bug, you are now doomed to spend the rest of your riding days thinking of what can i do next to the DUC and how the hell am I going to pay for it!!!!!!!!!
 

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My bike is a '03 620 with no mods. It's completely stock. What benefit would I have from opening my airbox or changing filters? Can I truly expect more noise (a plus ;D) and/or more horsepower?
Don't open the airbox unless you also rejet (I mean, get the fuel computer remapped). You can take the snorkels out temporarily, but you should notice a big lean spot in the powerband in the midrange.

I've tried all combinations of stock airbox/open airbox, stock pipes/slipons, and my conclusion is that the airbox modifications do a lot more for power than the pipes do. The pipes make it sound faster and maybe look faster, but does very little in the way of adding real power to a stock engine.
 

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Good Stuff Wheelinman.

I can notice major changes by playing with the different configs of my intake (airbox and stuff). If you lean out the bike to much, bad things man. Be careful, rejet.
 

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The '03 620 (and probably 02 and other Monsters) doesn't have the snorkels. There's a single entry slot in the airbox cover that runs the airstream across a resonator that's designed to reduce noise further. The resonator is a hollow rounded box moulded in to the cover.

Other than that, all the advice so far has been good.

As far as a K&N goes, it may or may not flow as much as stock, but the filter isn't the choke point of the intake (once the cover is removed or opened up). With the filter area of the stock filter (or K&N) it's unlikely the filter matters too much unless it's real dirty. I'd expect that the next most important choke point in intake flow is the fuel injection throttle body throats, and there's not much you can or would want to do about those.

Exhaust flow is probably not too important in the overall scheme of things, if you include valve size and timing and such, but the noise from aftermarket cans or pipes is worth the price.

With just the airbox mod and fuel mix tweaking ($20 at a dealer), your bike will probably top off around 120+, which is not too shabby for a 620 aircooled 2-valve twin.

Oh, that reminds me. Improvements in flow have a much greater effect at higher rpms where the volume of the flow is greatest. Anything you feel at <3000 rpms is probably imaginary.

-Don
 

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Good advice D.

Don't worry, right after I slapped those two filters on yesterday, I went to the dyno. Air/fuel was perfect.

-Patrick
 

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What type of riding is this opening up the airbox best suited for? I would assume it would be for the in town kind of rider? What does it do fuel consumption and maintenance routine? I'm curious because I have thought about doing the same mod. I'll be doing about one long tour on the cycle otherwise mostly on fast open twisty roads in the country. Not so much in town.
 

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The airbox mod (with fuel mix tweak) allows more air to flow at higher rpms, resulting in more power. In town it won't matter at all unless you're riding around at 7,000 rpms.

On the other hand it won't hurt anything around town either, except maybe reduce fuel economy a touch.

-Don
 
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