We aren't running a 500 HP diesel engine that we hope to have last hundreds of thousands of miles, under extreme conditions. We aren't discussing the suitability of a filter for long-term fleet use, and I wouldn't choose any filter other than the OEM if I were in the business of managing a fleet.
We're talking here about significant power gains at relatively low cost in a very small-displacement, high-performance, low-mileage motorcycle engine. Most riders will never even get close to putting 50,000 miles on a motorcycle. In that amount of mileage the possible additional dust contamination is never going to show up. We also have to look at our riding conditions: on-road, with clean air. We're not doing a tail-chase through the desert, sucking in massive amounts of particulate matter. And under those conditions, we want to change or service the filter more often, anyway, as both the OEM and K&N recommend.
Interestingly enough, most dirt riders use UNI and K&N-style filters and many dirtbikes come with an oiled-type filter from the manufacturer.
The image I posted simply shows that the K&N and similar filters flow more. That was the point. You've suggested that the amount is irrelevant, but it's not. It's not a fraction of an inch, it's 2" of water column, which is almost a 200% difference in pressure differential between OEM and K&N. When we are looking for performance, we'll take anything we can get. OEM is at 3" WC, the K&N is at 1". Big difference within the range of measurement expected.
High-flow type air filters make a measurable difference in performance. Racing engine builders and tuners use these filters routinely, if they use any filtration at all (in fact the OEM filter is the very first thing to go when modifying an engine for high-performance, followed by exhaust, fueling, and ignition time changes). This is a link to a before/after dyno chart showing the typical improvement associated with just an air filter kit. The Sonic 1.4L Turbo in the test picked up 7 HP, a big gain for minimal investment. The air filter and kit meet OEM specifications for filtration protection.
http://www.knfilters.com/dynocharts/69-4524_dyno.pdf
If we really are concerned about extracting high-mileage under more severe riding conditions, and we want to be conservative, choosing OEM is the way to go. However, going with a high-flow filter that meets OEM specs and nets a few more HP is unlikely to make any difference at all in the longevity of a motorcycle engine, given the vast majority of bikes will never see that kind of mileage and never be ridden in the kinds of conditions that would warrant an extreme level of filtration. A lot of motorcycle owners also use aftermarket oil filters to save a dollar or two, and the same can be said for being conservative there; OEM is best. But there's no power gain from using a different oil filter. We can show an immediate and measurable improvement from changing an air filter, but few riders are going to be discussing the condition of the valve train, cylinders, and pistons at 200,000 miles on their street motorcycles.
In any event, K&N and similar filters have been used in large numbers over the past few decades and the verdict's in; for on-road use of non-commercial vehicles, there just hasn't been any problem with them in this application.
Dakota_imp said:
Look at this another way:
The data Red Mist linked to shows a marked difference between the KnN and the Delco; the KnN let in over 17.5x the amount of dirt and the Delco had 1.37x the initial restriction. The data that I linked to shows 1.09x the restriction (I am too tired to calculate percent differences). I would argue that there will be some variation in initial restriction between different vehicles due to the cross sectional area of the filters. Different vehicles have different needs and expected air filter change intervals.
So, IF we NEEDED to increase air flow, an OEM could take a few different routes here:
1) Use the KnN and accept the inferior filtering but gain a bit of extra air flow (we still don't have any numbers to support we have gained any HP or that we needed to!)
2) Use the Delco filtering media but make the filter area twice as large. Now, we have retained the effective filtering and have very low restriction. How do you know that this isn't what Honda has done?
We could double the Delco filter area again to further reduce restriction (competent engineers would match a filter to air flow needs) but nothing we can do to the KnN will improve it's filtering effectiveness.
Interesting video showing sunlight shining through a KnN filter:
That, in fact, is precisely what the manufacturers have done. Compared to what we saw in bikes 20 years ago, both intake and exhaust systems are dramatically more efficient. The internal design and flow characteristics uncork a lot more power from engines of the same displacement. We're seeing ~200 crankshaft HP from some of the superbikes available today, from 1000cc. That's a huge increase what we were getting in 1994. It's both design and increasing the internal volume of the intake and exhaust systems.
But with a motorcycle we just don't have all the room in the world, so for any given application, increasing airflow is going to get you more power. The engine in this CB1100 is so detuned it's almost silly; we've got 1140cc of motor putting out 88 HP at the crankshaft. We could easily get another 20 HP with intake, exhaust, and ignition timing changes and I very much doubt the engine would suffer mechanically for it. The thing seems to be bulletproof and overbuilt.
We can think of the engine as a pump, and the more air it can pump, the more power it can make.
Let's just keep in mind that K&N filters meet or exceed all OEM requirements, and if we can breathe the same air our engine is inhaling (and our nose is a lousy filter compared to a K&N) then we're probably not going to have any issues.
