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The great (informative) K&N filter debate. (here we go again)

2093 Views 89 Replies 19 Participants Last post by  MN Willie
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It is with great pride that I'm able to start this conversation here today.

The purpose of this is to be informative, educational and last but not least controversial;)

There has been many a debate about the legendary K&N air filter with staunch arguments on both sides of the fence.

First, allow me to present some detailed instructions on how to properly maintain said filter (or any cotton gauze element type).

Then, I'll cover a case sample for further review and debate.

Last but not least I'll support everything with a short video from a man who is world renowned within the automotive industry (airflow research). When the OEM manufacturers have a problem they need solved this mans phone rings. His name is David Vizard, his level of experience and expertise is unmatched.

I know of several well respected figures who have done testing of their own in the past and those results have been repeated numerous times; here and elsewhere online. My intent is not to discredit those results in anyway. I'm merely presenting an entirely new set of facts and explanation of conclusion as to why it is the way it is and why those previous results ended up how they did.

Here's some initial food for thought: How much dirt and dust are we going to find behind this respectfully dirty K&N filter?
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Stay tuned for part 2 coming soon!
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Exactly what I thought. those fingers full of dirt will be like skinny tree branch with a fat cat on it.
I remember at the start of Covid there was a team of Japanese or Korean scientists measured how far the sneeze droplets can float in the air before falling to the ground. The same camera used for measuring dust particles flow through the filter could be very interesting.

I just noticed that the top cover can be disassembled. How come nobody came with some kind of inverted cone. This way there will be no turbulence behind the flat cover and fix the air flow issue. 3D printing anyone?

View attachment 42814
I don't think it's as much a turbulence issue as a lack of airflow. You need that open top for more airflow.

K&N actually has a line of automotive filters with a filter built into the top for more airflow. Something like that would work here, but it would increase the already high cost to something unreasonable.
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I don't think it's as much a turbulence issue as a lack of airflow. You need that open top for more airflow.

K&N actually has a line of automotive filters with a filter built into the top for more airflow. Something like that would work here, but it would increase the already high cost to something unreasonable.

They make tops that flow for the old carb vehicles with round filters. I have one on my 79 and 66.

The yamaha grizzly filter i mention is pretty bad too.

There is oe style


The K&N has 1/2 the surface area.
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I don't think it's as much a turbulence issue as a lack of airflow. You need that open top for more airflow.

K&N actually has a line of automotive filters with a filter built into the top for more airflow. Something like that would work here, but it would increase the already high cost to something unreasonable.
Maybe like this?

Arlen Ness filter. courtesy of cyclegear
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It's a simple set of equations that are required to calculate the requirements for area of filter required to support X power level on a given engine.

Perhaps some are not understanding fully that K&N employs said formulas to the design of each filter.

If the idea is that those engineers are simply slapping some filter medium/media into a particular shape, for a given application and then just crossing their fingers in hopes it works is absolutely false.

The other point is how much "surface area" the pleats provide. Hint: it's greater than you think.
It's also entirely possible to fall back on the surface area x flow/cm^2 equations without thinking about the bigger picture of air flow in something other than an open air situation.

For example, that lid with a built in filter does jack all on my 67 mustang with the hood sitting right on top of it.

Likewise, the airflow in the KLR airbox is such that a full mesh filter with breathe better than a K&N with a solid lid.
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It's also entirely possible to fall back on the surface area x flow/cm^2 equations without thinking about the bigger picture of air flow in something other than an open air situation.

For example, that lid with a built in filter does jack all on my 67 mustang with the hood sitting right on top of it.

Likewise, the airflow in the KLR airbox is such that a full mesh filter with breathe better than a K&N with a solid lid.

EXACTLY, very well stated; the K&N may well have the equivalent or better surface area but it FLOWS LESS inside a KLR airbox - this has been tested and is a fact. K&N did NOT design a filter for the KLR, they made a filter that fit the exact opening that was already there...

Dave
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K&N did NOT design a filter for the KLR, they made a filter that fit the exact opening that was already there...With sufficient surface area for the airflow requirements
Precisely.

Now, the KLR airbox design is another can of worms entirely. ;)

Best wishes
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I do have to wonder if anyone has ever redesigned the intake and air box on the KLR.

Obviously a lot of us have modded the air box, but I wonder if there's a more efficient way of reconfiguring the filter and airbox setup.
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Like this,




Best wishes as always and remember ride hard ride often for life is short.
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Sure there is, but you will still be limited by the amount of air the carb and intake port can pass. Drilling holes in the top of the airbox and using a Uni filter pretty much eliminates the airbox and filter as the choke points. And that only nets a couple HP. To get more, you have to start modifying the intake, cams, increasing compression, etc. The guys who have managed to push the output of their KLRs to more than 40HP had to do those things.
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Sure there is, but you will still be limited by the amount of air the carb and intake port can pass. Drilling holes in the top of the airbox and using a Uni filter pretty much eliminates the airbox and filter as the choke points. And that only nets a couple HP. To get more, you have to start modifying the intake, cams, increasing compression, etc. The guys who have managed to push the output of their KLRs to more than 40HP had to do those things.
Yep; after the L mod and snorkle removal, the airbox isn't a bottleneck anymore.....at least not on moderately modded KLR's.

Dave
.With sufficient surface area for the airflow requirements Sufficient? sure but still not enough to beat the oiled foam filters for flow. ;-) They didn't change their pleats or construction to make a bespoke KLR K&N filter - they used their standard media and shaped in an oval cone that fit inside the KLR's airbox and matched with it's filter seat.

Dave
Best wishes as always and remember ride hard ride often for life is short.
sure, and stay waaaay away from the water crossings and don't ride on rainy days. :rolleyes::rolleyes:
sure, and stay waaaay away from the water crossings and don't ride on rainy days. :rolleyes::rolleyes:
Man conventional wisdom is a scary thing.

I have a river crossing most of the year just to get out of my property(see previous posts). I've been caught in heavy AZ monsoon storms multiple times at 70mph on the interstate and on the dirt roads leading to and from my place.

.With sufficient surface area for the airflow requirements Sufficient? sure but still not enough to beat the oiled foam filters for flow. ;-) They didn't change their pleats or construction to make a bespoke KLR K&N filter - they used their standard media and shaped in an oval cone that fit inside the KLR's airbox and matched with it's filter seat.

Dave

This bike came alive after I cut the box up(jetting to match). Other than the K&N filter this bike is completely stock and I can easily accelerate from 60-90mph on the interstate with all luggage attached (however, not loaded heavily). Maybe 25lbs on top of the boxes.

The stupid snorkel doesn't do much, the L mod does a better job but it's still not enough CFM to properly supply this 650cc engine at anything above 5k without excess restriction. On a flow bench we would see the mercury rise as it transitions from free flowing to restriction.

Typically, on an automotive flow bench we test at 28in/H2O However, you might be aware that one can easily adjust the "test pressure" of the flow bench to something like say 10in/H2O which would result in higher flow numbers than the test at the industry standard of 28in/H2O

Since I no longer have a stock air box to measure can someone tell me what the opening dimensions are of the factory airbox inlet (snorkel removed)??

Next, tell me what size holes we are drilling for Lmod as well as quantity.

I have airflow formulas in my work book for calculating "flow through an orifice" accurately.

I'll post up the 'area' available numbers as well as the figures for flow/CFM through said orifices that compensate for efficiency.
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This is all you need to do…IF you want your airbox to free-flow a bit better. These 1in air filter vents can be bought on Amazon.

No need to hack the entire thing off! 😆
But hey, do what works for you 👍

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This is all you need to do…IF you want your airbox to free-flow a bit better. These 1in air filter vents can be bought on Amazon.

No need to hack the entire thing off! 😆
But hey, do what works for you 👍

View attachment 42861
What's the purpose of cutting holes if you're just going to plug them back up? There's not much if any CFM gain there.

No need to hack the entire thing off! 😆
But hey, do what works for you 👍
💯 Agree. By no means am I advocating anyone do what I have done.
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What's the purpose of cutting holes if you're just going to plug them back up? There's not much if any CFM gain there.
They aren’t plugs…although they do look like it in the pic.

They aren’t plugs…although they do look like it in the pic.

Basically a plug, almost no air goes through those.
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Basically a plug, almost no air goes through those.
They will when the filters are removed! 👍
I’m planning on installing them to keep big $hit from dropping into the box. Not like that’ll happen either, but what the hell…

It probably won’t help much, KLR’s will always be slow 😆
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What's the purpose of cutting holes if you're just going to plug them back up? There's not much if any CFM gain there.


💯 Agree. By no means am I advocating anyone do what I have done.
You get good result with the open air system eliminating the air box volume limitation. How is your torque on lower RPM?
I had K&N with no air box long time ago with a small two stroker. Could not get it set correctly. It lost the torque on lower RPM and if there is an advantage in higher RPM it was probably so small I could not tell.
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