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Discussion Starter · #1 ·
Hi all, .

New member here first post!:D

I installed a K&N air filter this afternoon and noticed a large snorkel like tube on the air box to allow the air flow into the box, my last bike (ZX6r) didn’t have anything like this. If I remove/shorten it will this help increase air flow/power gain? And has anyone else done this?? I’m a novice when it comes to mechanics but get a kick out of doing it myself.

Thanks,
 

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i cut mine flush and nothced out the front little plastic tank trim piece to make it a bit easier for air to get in, I did not do pre a post dyno runs but I do not see any way this can not help
 

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My klx250 has a snorkel type of rig on the air box, and several people have done the "air box" mod for more air flow. But peoples opinions vary if it does any good, bad, or anything at all. Like fizzer said, without proper testing, there is no way to prove one way or another.
 
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...noticed a large snorkel like tube on the air box to allow the air flow into the box ...
hmmm ... does it go upward? I'll have to go look at mine. I've been wondering how deep of a creek I could cross. On my KTM 950 I could do 36" streams. Here's pic of Matt finding out that 39" is too deep. We shifted 10' downstream and both of us crossed just fine



here's the video

 

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Air boxes on most modern streetbikes are designed to mold the airflow so it is smooth and not very turbulent as the air enters the fuel injectors. This is referred to as a "still air" air box. It obviously is NOT actually "still air" but it does smooth out the airflow.

Cutting the snorkel off will cause turbulence and probably reduce the power output.

Further, if cutting the snorkel actually did give you more air flow and you did not also modify the fuel maps to compensate for the increased airflow, then your bike will be even more lean than the stock fuel map settings and they are already set too lean. Too lean will also reduce the power output.

On a dirtbike the airbox is not a "still air" design as it is mostly just a box to hold the filter in.
 

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I tested 2 different mod. Cut the whole top off and open the front area only. I did felt some gain from opening the top. But it is a bit harder to tune since the air move arohnd a bit more. Not still air like Moto mention.
 

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This reminds me of another forum, where a member drilled holes in his frame, in everything, to reduce weight...

If I saw before and after dyno charts, I'd be game. M
I remember seeing that somewhere. Was it a Kawi or something like that?

Just so you know... to of the airbox is pretty cheap. I got one with some spare stack to test.
 

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Discussion Starter · #11 ·
Thanks for the feedback guys!

I had done it to my KLX years ago under the advice of a mechanic (as I don’t do mods myself unless I’m 100% sure what I’m doing). I was merely curious as to see if others had done it to the FZ/MT and the Pros and cons of it. I plan on getting the bike on the dyno once I get an Exhaust, re-flash unit and possible quick shifter added.

Thanks again!
 

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In my experience, dealing with many years of fuel injected engines/designs, and doing some serious mods, mostly with turbo charging, these factors are more important than air box design.

Few are really designed to capture wave effect charging, and they tell you about it if they do design it into the air box.
As long as the sensors are in place, things work well. (MAP, IAT etc.)

Air flow is going to be turbulent, and this idea that they are designed to smooth it out over injectors is nearly impossible. (Sure, the venturi stacks can accelerate air, and that helps with chamber filling effects, but let's face it, you are dealing with all sorts of things out in the flow, creating turbulence constantly, and variable turbulence at that, just open your throttle more or less, and you create COMPETELY different flow patterns and effects, so it's not that critical.)

With three stacks tuned to flow/fill at different rates, Yamaha clearly knows this. Add longer runners, and you would improve tourqe, shorten them, and get more top end power, it's common theory, and it works pretty well on a 4 stroke, 4 valve per cyc. engine.

The more air you allow in the air box, the more you can add to the fuel, and that's more power, and less "pumping loss" to get it, so you get the power sooner, and more of it goes to the wheel. (IE: You get more.)

In my view, from what I've seen of this air box, it's designed for noise control, not to smooth out air. The chambers and snorkel are classic sound control fodder.

If you want smooth flow, get three cone filters, remove the box, and clamp them to the three intake venturi's to filter the air. It will give you the most flow, and likely the highest power output at the wheel. Now the issue is where to put the sensors? They should read a combination of the demand for air for the engine, and you can't just place them in the center stack, and hope to get a valid reading there, since they are needed across the entire RPM range, while the center stack would be midrange power/flow tuned. (All things being equal.)

Of course, they are not. And that's the fun of discovery! :)

The box tops as noted are cheap. Cut them up, and let's figure out what's flowing the best, and/or is the best compromise of noise control lost, to power gained.
 

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PS: The O2 sensor is going to trim fuel to keep it working. And that trim figure is going to set the base line fuel map if they designed this in any sort of modern way at all.(IE: It's going to have more fuel than stock, based on the fuel trim from part throttle use, moving up the base fuel map.)

I'd also be surprised if this engine did not encorporate knock sensors, to keep it from being used too lean, and control timing? It appears the timing can be changed with a re-flash of the ecu, so it's not fixed in stone.

Also up to the rate of flow of the fuel pump and injectors, and based on the WOT fuel map, you would have to figure out how much they can flow before you would run lean by adding more airflow. (Again, the base map might be lean, but I'd be really surprised if it does not "learn" from the part throttle, and move up and down a fixed scale depending on engine tune, altitude, pressure etc.)

This would allow a bike to go from Texas, up to Colorado, and still run well, even though you completely change the volume of air to fuel needed for the engine. (And since it would be ridden there, it would happen and the rider would not notice that the sea level map is "richer" while the high altitude one is "leaner" since the MAP sensor, AIT and O2 feedback keeps the engine within the programed fuel map range.

Throw on a open air box, and it's going to adapt.
Put on a pipe, and it's going to adapt.

But it can only adapt into the range of data programmed into it.

This is why I think the guy in OZ who "Fools" the O2 sensor into running slightly richer than normal is the only real way to get any EFI system to work well over time. Sure, you can program the WOT and even part throttle for your bike on a specific day, temp, and pressure. But when that changes, you have to re-program the bike again to get it right again. With the "fooled" O2 sensor, it's going to always adapt to the changes for you, and provide the best option day to day.
 

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My klx250 has a snorkel type of rig on the air box, and several people have done the "air box" mod for more air flow. But peoples opinions vary if it does any good, bad, or anything at all. Like fizzer said, without proper testing, there is no way to prove one way or another.
The Klx250 is a bad example. It was never intended to be high performance. The intake area of that snorkel is actually smaller than the throat of the carburetor. Why would they do that? Some think for reduced sound level. I replaced mine with the snorkel from a related 300cc off road only model. Some people use no snorkel and some leave the top off the air box altogether.
 

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The Klx250 is a bad example. It was never intended to be high performance. The intake area of that snorkel is actually smaller than the throat of the carburetor. Why would they do that? Some think for reduced sound level. I replaced mine with the snorkel from a related 300cc off road only model. Some people use no snorkel and some leave the top off the air box altogether.
Believe it or not, the smaller intake area improves airflow within the box. Think about the venturi effect. On my racing sidecar, when I reduced the intake area to the oil cooler, air flow improved and I actually got more air through the cooler. Temps dropped nearly 10 degrees.
 

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Yes, out in air flow, over and around the cooler, you can get more with less. Any design that creates a low pressure area behind the cooler, even with a smaller than cooler sized inlet, will get high flow v/s one that has a large funnel opening, that looks like it should flow, but if there is no lower air pressure BEHIND the cooler, it's not going to flow more. Period.

But where an engine is creating low pressure by running, it's another story. It's about pumping losses then. How much energy is lost to just creating that low pressure v/s having some sort of "positive" pressure created inside the box of clean filtered air ready to be added to fuel.

Because air boxes are sealed up to keep filtered air clean, they by their very nature can't be designed to create their own low pressure zone inside them. There is no exit air being drawn out. (The engine is running on that air... LOL)

The harder it is to create the low pressure area, the more pumping losses you have, and the lower the engine output at the wheel.

SO, if you carefully studied every inch of surface on a vehicle, you would find places that create low and high air pressure as air flows over and around the vehicle. Put the air intake at a high pressure point, and the exit at the low, and you get amazing flow, even with small openings of shapes and sizes that don't always look like they make sense either.

Take a NASCAR air intake for example. IT's just a small slit at the base of the windshield. Narrow. No NAACA ducts, nothing fancy at all. But it's right at the point where air flow over the car creates a high pressure air bubble right there. Not any wider, further forward, or up the windshield etc. (It's also why 99.9% of vehicles have their HVAC system air intakes in this same area, free flow into the inside of the car, a low pressure area from the high pressure area created by air flow over the car.)

Problem is. the hood of a NASCAR vehicle has more surface area than most of our street bikes. :) Not much area for us to work with to generate high pressure areas that can feed the intake point of our air boxes. And most ram air systems don't work until the bike is going triple digits first.

So, open is free power at lower speeds, reduces pumping losses, and low flow restriction filter media helps too.

That's just my .02 cents worth.
 

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Yes, out in air flow, over and around the cooler, you can get more with less. Any design that creates a low pressure area behind the cooler, even with a smaller than cooler sized inlet, will get high flow v/s one that has a large funnel opening, that looks like it should flow, but if there is no lower air pressure BEHIND the cooler, it's not going to flow more. Period.

But where an engine is creating low pressure by running, it's another story. It's about pumping losses then. How much energy is lost to just creating that low pressure v/s having some sort of "positive" pressure created inside the box of clean filtered air ready to be added to fuel.

Because air boxes are sealed up to keep filtered air clean, they by their very nature can't be designed to create their own low pressure zone inside them. There is no exit air being drawn out. (The engine is running on that air... LOL)

The harder it is to create the low pressure area, the more pumping losses you have, and the lower the engine output at the wheel.

SO, if you carefully studied every inch of surface on a vehicle, you would find places that create low and high air pressure as air flows over and around the vehicle. Put the air intake at a high pressure point, and the exit at the low, and you get amazing flow, even with small openings of shapes and sizes that don't always look like they make sense either.

Take a NASCAR air intake for example. IT's just a small slit at the base of the windshield. Narrow. No NAACA ducts, nothing fancy at all. But it's right at the point where air flow over the car creates a high pressure air bubble right there. Not any wider, further forward, or up the windshield etc. (It's also why 99.9% of vehicles have their HVAC system air intakes in this same area, free flow into the inside of the car, a low pressure area from the high pressure area created by air flow over the car.)

Problem is. the hood of a NASCAR vehicle has more surface area than most of our street bikes. :) Not much area for us to work with to generate high pressure areas that can feed the intake point of our air boxes. And most ram air systems don't work until the bike is going triple digits first.

So, open is free power at lower speeds, reduces pumping losses, and low flow restriction filter media helps too.

That's just my .02 cents worth.
Great write up mate.
 
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