K&N Filters and LOSS of HP

I noticed on page 73 of the February 2012 edition that you experienced a loss of 2.3 bhp when you added a K&N filter to the ZX-6R.

This is not the first time I've heard of this, Michael Wheeler aka Lord Duckhunter of www.rc51.org and www.919.org fame first brought this to my attention several years ago.

Was V&H or K&N asked about this?  

Maybe they're soaking the thing with oil, restricting air?  

I use the stock air filters.  Although, Kawi wants like $50 bucks for one to fit the Rex!  

joegresh:
Maybe they're soaking the thing with oil, restricting air?  

I use the stock air filters.  Although, Kawi wants like $50 bucks for one to fit the Rex!

I don't think that is the issue.

"Lord Duckhunter" and a fellow in California did a lot of dyno testing, and they experienced similar results with many bikes and the K&N (and other aftermarket) filters.

I believe K&N even offered foam for the filters on some models (RC51?) to try and correct the issue -  




Here is a link to a good write-up by LDH

I understand this is a very touchy subject as advertising dollars are at stake.  

If more air always produced a HP gain....we'd ditch filters altogether.

[edit]

What I mean is that if an engine is well developed for a specific airflow rate, changing one thing that increases airflow could upset the balance.  One small example is that if air flows too freely, there may not be enough turbulence to mix the fuel and air.  There are also countless other variables.  

I've had a similar issue with my '08 B-King GSX1300.  A K&N filter along with air box mods caused very slightly higher top-end rwhp, but at the expense of a drop in rwhp and especially torque in the low and midrange.  I had the bike dynoed for optimum a/f mix ratio with the K&N and open air box.  Now, I'm thinking about reinstalling the OEM filter and closing the air box back up to see if I can restore low and midrange torque, but will have to retune again so that my a/f mix is not too rich.  It's a troubling little experiment I've got going.  Any suggestions or thoughts from anyone?  

This is typically what happens with the CV type carbs. If you allow tons more air to flow, the amount of air exceeds the ability of the carb meaning that it needs a certain amount of restriction to actually work. People forget that when CV's first came out, even on the same bike but a different year, they were often 2-4mm larger.

On a XJ forum I also belong to, it's the subject of the day more often than not. Guys install pods only to see their bike run like crud and they won't listen to what's required to straighten it out.

jeff  
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'74 RD350 in great shape & 1975 GT550 restored&built up and a beautiful, low mileage '73 CB350(same as my 1st bike), another '75 GT550 taken in pymt for port work on an H1. All original, nearly flawless '75 H2, '74 H2-fire breather, 82 Yamaha 650 turbo running 18psi, 75 H1 restored, 75 H1 for restoration

Well the way I think of it is the Fuel doesn't just fall into the cylinder, it is sucked in and with no filter it, its sucking power just went out the carb.

It isn't like the old days when we had plenty of fuel, everything is running lean now. Let the Engine suck the fuel its needs first before you give it more air.

I put my stock filter back on my DRz-400 Motard because it filters better and I believe it runs a bit richer.  
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joegresh:
Maybe they're soaking the thing with oil, restricting air?  

I use the stock air filters.  Although, Kawi wants like $50 bucks for one to fit the Rex!

I think you got that wrong Joe. Those K&N filters flow more air and dirt, you can ruin an engine in an afternoon on a dusty Motocross track.

Don't ever tell anyone to not put oil on a K&N filter. K&N even makes a Spray on Oil for their filters.

For dirt use, the stock filters I believe are best and much better than a K&N. Use the K&N on Pavement with clean air...  
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My ZRX ran crummy off idle when I first got it.  Some whiz-kid had drilled holes in the air box lid to "let 'er breathe"

I still have blue masking tape over the holes, runs much better.  

joegresh:
My ZRX ran crummy off idle when I first got it.  Some whiz-kid had drilled holes in the air box lid to "let 'er breathe"

I still have blue masking tape over the holes, runs much better.

I have a 1" by 4" hole cut in my KLR air box and it runs great with a DG Pipe and a JD Jet kit. I am still running my stock filter because of dust on some of my rides.

My Zuki Motard also has a hole cut in its air box and a Yoshimuria pipe with a JD Jet kit. And it runs great, turned 10,000 miles on it last fall. I have a K&N for it but run the stocker so it will run a bit richer and filter better.

 
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joegresh:
My ZRX ran crummy off idle when I first got it.  Some whiz-kid had drilled holes in the air box lid to "let 'er breathe"

I still have blue masking tape over the holes, runs much better.

Whats your ZRX? Is it a 4 cylinder carb bike or fuel injected?

Even if drilling the holes would have helped, it would only help on the top end where the bike couldn't get enough air if someone had given the bike more fuel in that area too.

The whole range, low, mid and high has to be matched to the amount of air comming in from your holes and exaust changes. If it isn't, leaving it stock is always the best bet in my book.

The changes made on my KLR and my DRZ are from top to bottom and both run like they should all the way though. I don't take the credit, the instructions were spot on with the jet kit on both bikes.

If your ZRX was an 1100 or 1200, that would be more work than I would want to get into, so taping up the holes would have worked for me too.    
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Carbs on the zrx1100.  I have to clean the Magna's cabs, a man has only so many V-four carb teardowns...  

joegresh:
Carbs on the zrx1100.  I have to clean the Magna's cabs, a man has only so many V-four carb teardowns...

I really work hard at keeping my 1986 V-Max in running condition so tearing down the carbs won't be on my list with that bike.

Now I have an XR-200 Honda that I only start every few years, (No Place To Ride It) and each time I set out to start it again, I first dump out the gas and tear down the carb and clean out the jets.

Once I get it started, the tires aired up and the bike cleaned up, I'll ride it around the yard and up and down the street a few times. Then ride it everyday for a couple of weeks, then somehow forget about it again for a few years.    

I think next time I get it running I'll try to sell it for a fortune.  
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