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Discussion Starter #1
So I cleaned my air filter on the 05 c50 the other day. It's in need of replacing. I'm looking at the k&n. Does it really make a notable power difference? I'm running stock pipes that I debaffled. Will I need a fuel mapper? Is it worth doing or am I better off sticking with oem?
 

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I really can't answer your question, but I can tell you my experience. When I bought my second-hand '08 C50 it had a K&N filter in it. The bike exhibited pretty frequent exhaust popping on deceleration, fuel mileage was not that great, and it always felt a little sluggish on acceleration. I cleaned the filter thoroughly, but that didn't change things. Eventually I bought an OEM paper filter. Immediately the popping went away, gas mileage went up, and I could feel significantly more power throughout the rev range.

Your experience may not be the same.
 

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Love me a K&N thread.

OK so here's the layout. In the left corner you have people who will tell you to forget it. Here are their reasons:
  • K&N filters are oiled media filters, not paper. They require maintenance and if you don't maintain them, they will permit more dirt into your engine.
  • K&N filters are high flow, which by definition means bigger holes. Even with proper maintenance they will let in bigger particles.
  • (Unrelated to the Volusia/c50) On vehicles that have a mass air sensor some people have seen these sensors fouled by by oil from the filter
  • Even adding a K&N filter will only increase your power by about 4 hp, which they will say you can't actually feel.
They will usually cite the two studies that have been floating around the web for years. I have the link handy for one of them here: K&N Air Filter Review - Debunking the Myths (and why OEM is better). Do note that K&N comes out looking pretty poor in these tests. Also note that none of the other brands make filters that fit the Volusia/c50 air box, so forget about them and just compare to paper filters.

In the right corner we have those who like K&N air filters. Their arguments go like this:
  • A properly maintained K&N filter will last forever, and unless you ride in incredibly dusty conditions all the time, all you have to do is spend an hour a year to do this.
  • While K&N air filters do permit larger particles they aren't large enough to matter to longevity of the engine.
  • Mass air sensor issues are anecdotal, easily fixed, and only happen if you really over oil the filters.
  • A 4 hp increase on a Volusia/c50 is a 10% increase.
  • The Nico club study shows what a K&N filter will do with a literal 1 lb of dirt on it. Hopefully you never let it get that bad. I would expect any filter with a pound of dirt on it to not function correctly, and I don't care by how much.
I put in a new K&N air filter in my 2003 Volusia last week and have done a couple of test drives so far. I can tell you that butt dyno says that yes it does make a difference you can absolutely notice. When I am going about 25-30 and I give the throttle a good twist I am suddenly going 55 in 2nd gear (I do have the DJ Drive mod). You won't increase your top speed with a new air filter but you will increase your acceleration. On the highway I can actually accelerate from 75 to 85 now, not just hope I eventually get there. (Again, DJ mod will make a big difference here). Note: to accelerate at any appreciable rate from 75 to 85 with the DJ Drive mod I need to be at WOT. 7/8th of the way to WOT there isn't much acceleration, but at WOT it suddenly feels like you twisted its tail real good.

The reason I chose to do this mod is because from the research I've done the fears of K&N filters killing engines are way overblown. I have not seen even anecdotal accounts of an engine failure ever being directly attributed to a K&N air filter. I took the risk on it because for $35 I could get a new paper filter, but I scored a brand new K&N on eBay for $43. They normally go for about $55.

You will need a fuel controller with it because your bike will not run correctly without that. For 2001-2004 you will instead need a jet kit. Rejetting a carb is a super simple process, and there is no voodoo about guessing the correct jet sizes as others have done it all for us. Take a look at the Rejetting matrix post here: Rejetting Matrix

Note that those that are familiar with the Harley world will have the mindset that your order of improving horsepower for your bike goes like this: get an exhaust, then get a fuel controller/jet kit, then finally do the air filter. I am not 100% sure how this applies to Harleys, but looking at the rejetting matrix post you can tell that a freer flower exhaust won't do nearly as much for you as a K&N filter + jet kit. I assume on the c50 it is similar. The stock jets are I believe 28 pilot jet, 125 or 128 main jet (not 100% certain which comes from the factory). You can get a very small improvement just by going to 28/130 and a Dynojet needle. I did this with everything else stock and the main improvement was that I didn't need to use the choke nearly as much to get the bike going. Power-wise it felt the same.

But look at the rest of the combinations: the second largest jets are used with an airbox mounted K&N filter: 37.5 pilot, 150-155 main jet. People will tell you that the main jet is only for near WOT and doesn't affect the rest of the range, but it really does as the needle goes in/out of the main jet holder. And remember these are not linear gains but square gains: A = pi * r^2. Going from a 128 to a 150 main jet you gain 37% more area which directly translates into that much more fuel drawn in. Basically you will always draw more fuel in with this setup, which will by definition result in more torque at higher RPMs. Note that adding an aftermarket exhaust with a stock air filter makes you go up just one size jet from the stock recommendation (or two sizes from the factory jets). It does almost nothing on this bike, except make it sound different.

Small anecdote: I didn't have a 37.5 pilot jet handy when I put in the K&N air filter and the 150 main jet. I put in a 32.5 jet and used the idle mix screw to try to adjust it. It ran fine but definitely wanted to be all the way warmed up. How do I know I was drawing in a lot more fuel? On deceleration it backfired like a motherfucker. Yesterday I got and put in the 37.5 and now it's back to quiet pops once in a while.

Here are the potential risks I see specifically for the Volusia/c50 with this mod:
  • Theoretically you are going to be pushing more power through the same engine, and the bottom end was not necessarily engineered for this. I dismiss this as horse feathers because the power increase is a mild 10% at peak. If this engine was designed with a less than 10% safety margin, they would be failing all over the place.
  • Dirt in the engine will ruin it faster. Maybe but I am in the right corner (see above) with never having seen anyone attribute engine failure to a properly maintained and properly installed K&N filter. Worst case, yes this will cost me $700 to get a used engine off eBay, but then I'll have two motors, one to rebuild, one to run at any given time.
  • Gas mileage will suffer. Maybe a little, but going 50mph should not really consume any more fuel than it did before. The bad mpg comes from going "oh I can really rip this thing now!" and riding at WOT more than you would before.
  • Some Amazon reviews for the SU-8001 K&N air filter state that they don't quite fit into the Volusia airbox, but fit perfectly into the c50 one. Some had to go as far as cutting off a bit of the trim off to make it fit with a scalpel. I did not personally experience this, but be prepared I guess. Worst case, buy a c50 airbox for your Volusia to make it a perfect fit?
I encourage you to make your own decisions about this. Worst case, you can always go back to stock and sell your filter and fuel controller for not much less than what you bought them for.
 

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If you want a more powerful, faster bike, you will have to buy something else. The c50 is a fun ride but you can't tweak it enough to drastically change it from what it is designed to be.
 

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The only thing a K&N will do is separate you from your hard earned money. Your '05 is fuel injected, so throwing one into your airbox will cause the bike to run lean. You will also need to add a fuel processor, as the simple 32bit ECU onboard cannot compensate for the additional air flow. Throw on a set of pipes and you just burned a grand and gained a whole 4hp. The throttle response will be a little more crisp, but despite what the butt dyno says, it isn't going to run any faster.

If you are looking for more power, save your money and get a bigger bike.
 

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Just to put the "K&N won't harm your engine" debate to bed, this is the throttle body from my 1995 F150, after running a K&N filter in the air box for about 30k miles. Notice the amount of dirt stuck to the oil residue?? It was like that all through the intake runner.
 

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Discussion Starter #8
Thanks for all the response folks! I believe I'm just going to stay stock with this bike. I've decided it's time for more bike. Now how to pay for it??? :D:D
 
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