Simply put on a purely scientific scale the OEM type paper filters keep the most particles out of the engine. That said the extra debris a K&N filter lets in is so insignificant that it makes no difference to engine life. Think of it like spitting in the ocean vs peeing in the ocean. Either way you are not changing the volume of the ocean although a scientist will tell you that you are.
K&Ns have been demonstrated innumerable times to be less effective at filtering than paper filters. There have been instances where KN filters actually provided more airflow than a standard paper filter but this will depend totally on the design of the OEM filter. IOW, if the OEM filters' design requires the use of a paper filter that does not have sufficient capacity for the engine, the KN may provide a power (and wear) increase. OTOH, if the OEM design does provide sufficient capacity - which most do - , a KN will do nothing but degrade the quality (cleanliness) of the air getting into the engine.
The oem filter will let enough air pass for max engine power, what are you gaining by putting a filter in with more or bigger holes
The reason I used the K&N filter is due to the large turbo/hi boost. I don't know how restrictive the paper filter is in this regard.
When I first got the 308 I bought a K&N. It didn't fit. You could force it in but it wasn't a perfect fit so I dumped it and went back to the UFI. In regards to performance, at any given point in time you have two cylinders drawing in air, one 90 degrees behind the other. You have a peak hp rpm and a redline rpm and it would seem to me that the engineers who designed this engine wouldn't then attach an air intake that was incapable of meeting the demands of those specifications. So, in my opinion, the performance increase claims made by K&N are wildly exaggerated.
Paul, I tend to agree. But I don't think they considered adding 22-25lbs of boost which is about double the needed airflow over naturally aspirated engine. I doubt the K&N is appropriately sized in that regard either
It's simple. A fitter is a resistance to flow. The resistance is dependent the permeability or porosity of the filter. Lower resistance means greater porosity. But the greater the porosity the poorer the filtering ability. Porosity depends on the size of the holes in the filter element. If you want lower resistance with the same area you have to increase porosity. If you want lower resistance with the same porosity you have to increase the area of the filter. K&N use an element with greater porosity to reduce flow resistance and tries to compensate for the reduced filtering ability by applying oil to the element which makes it "sticky". It somewhat similar to furnace filters that use electrostatic charge to make the filter "sticky" to dust particles. But in the case of the K&N the stickiness doesn't generally compensate enough to bring the filtering ability up to that of the dry OEM filters.
Expanding on my previous comment with respect to this post, when the engine is sucking in air it "swallows" a certain volume of air. The key here is "volume". With a filter of lower resistance the pressure drop across the filter will be lower. Since the density of the air, thus the mass of air in a specific volume is higher if the pressure is higher, reducing the pressure drop across the filter will increase the mass of air taken into each cylinder. Then, assuming that the mixture (A/F ratio) is corrected for the actual mass ingested (like K-jet with lambda control) you inject more fuel and can get a little more power. With carburetors, not so much.
Well I'm not familiar with your system but it would seem the boost is downstream of the filter and it's being controlled by maybe a waste gate or something like that so the filter is not the limiting factor but yes, in such a case the original intake system is not speced for those parameters.
Based on the square inches of filter area, the stock (carbed car) paper filter is good for somewhat over 400 rear wheel HP, before you start getting above 1" Hg (~3%) pressure loss across the filter. About ~90 sq-in of simple surface area. Based on dyno experience on other motors. If you have an injected car, figure 90 sq In of simple surface area of your filter is good for 400 RWHP I wouldn't ever run a K&N filter, they were rejected for OEM use by Chev and Chrysler because of lack of filtration, plus to make them work even that good, you have to oil and wash them regularly Doug
I tend to agree Doug. Surprisingly they are approved on certain aircraft and you would think they have a higher standard.
Aircraft run in a different environment and most have carb heat or alternate air systems that bypass the filter entirely. A car is bound to the ground behind other vehicles that are constantly kicking up dust and debris so you wouldn't ever want to run unfiltered intake air for any significant length of time.
Even so it's only take off and landing and they don't do that following behind someone kicking up dirt. Cars operate in that environment 100% of the time. Look at a typical Cessna or Piper Aircraft that could have an O-520 which is an eight and a half liter engine and the filter is tiny compared to a car so they have to be pretty free flowing.
K&N will give a slight hp boost, Mike C and I demonstrated that 15 years ago. But it's academic only. Not something that you can feel. Take a look beginning at post #107 https://www.ferrarichat.com/forum/threads/dyno-s-this-weekend-for-308-intake-tb-mod.88743/page-5
If you still have the original (restrictive) air box on a carb car, air filter differences are irrelevant.
The carb airbox isn't that restrictive. The inlet sq inches are good for 400 HP, again, based on dyno results from other air intakes. The air flow area on the sides, between the filter and the airbox, could be larger, but doesn't look like it is an issue, from experience, but I have no actual data to back that up. I seem to recall, but am not sure, that there is a sound baffle between the inlet oval, and the air filter, that may restrict flow by some unknown amount. The flapper valve for the heat riser may also create turbulence and restrict flow by some unknown amount. Only way to tell for sure is to measure pressure differential inside the air filter element, vs atmosphere or boost pressure, at high RPM WOT. And differential more than 6" water column, is restrictive. Doug
