| Posted: Sep 27 2004 at 9:52am | IP Logged
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When I was trying to decide whether or not to use a K&N a couple of years ago I came across this site:
http://www.bobistheoilguy.com/airfilter/airtest3.htm
This guy really took a common sense approach to testing this. It seems that at least in this test they do flow more particulate matter. This doesn't answer the question of how harmful it is to your engine though. But it seems reasonable to me that less dirt in the cylinders is a good thing. If you're going to keep your truck for the long haul (pun intended), a high-flow filter may not be for you.
The other issue is performance. If you are trying to eek out an extra 10 or 20 hp at 6000 rpm, a high flow filter may be for you. If you mainly rely on mid range torque for you acceleration a K&N is not necessary. K&Ns literature gives cfm ratings for stock panel paper filters. If you do the math (I have) you'll find that flow restriction is only an issue at very high rpms.
http://www.knfilters.com/facts.htm
Note that these are average numbers. Now the cfm requirement of the Titan can be calculated by multiplying the displacement (341 cubic inches divided by 1728 for cubic feet) by the rpms divided by 2 (1 intake stroke out of 2 crank revolutions). This yields the cfm requirement for the Titan engine at that particular rpm.
For example: (341 / 1728) * (6000 / 2) = 592 cfm at 6000 rpm. That is not within the average clean paper panel filter (or K&N for that matter), but the Titan's panel filter is larger than the average unit. An average unit would be more like a mid size sedan like a Maxima. I originally did the calculations for a Maxima and found that it needed 318 cfm at 6000 rpm, which is within the average. Since I do not know the cfm rating on Titan filters, I cannot say for sure about them. But I would venture a guess that it is near 600 cfm. More info here would be interesting though.
I have performed back to back testing with Maximas and found that there may be a slight performance increase on the high end, but measuring the acceleration difference throughout the rev band yielded a different result. By leaving it in 3rd (it was a manual) and letting the engine pull from 2000 to 6000 rpm, there was no difference in the acceleration until maybe above 5500. And after repeated tests I was still unsure about that high end gain. I really enjoy high performance, but I will not sacrifice engine longevity to get it, especially if the power increase is only marginal, and at an rpm I am almost never at.
There are other flow issues that should be considered. Easing restriction does not always produce more power. It does in many cases, just not all. Since naturally aspirated (non-blown) engines fill the cylinders based on vacuum, pressure in the induction stream is essential. A buddy of mine had a 427 race Camaro when I was in school that ran stronger on a single 4 than two 4 barrels. Why? Pressure. Just like a nozzle increases the pressure of a water hose, a smaller intake can sometimes pressurize an induction system. In the short window an engine has to fill a cylinder this pressure is a big issue. So it is possible to actually reduce power if air flows too freely. In other words, there could be an offsetting decrease in power in the low end or mid range with a K&N filter. I doubt it though. Most of the airflow velocity and turbulence issues are handled by our very effective variable intake system.
For me, I guess I have decided K&N filters are not worth it. The extra dirt in the engine is what really gets me. K&N says its filters trap more particles once they get a little dirty (they don't mention what happens to flow), but that's just another area where I'm skeptical. If the power increase was across the band and very fat (and its not), I would still be leery of this dirt issue. I am planning on keeping my Armada as long as it will run. If I still own it 10 years from now with let's say 300k on the odo and it uses little or no oil, I will be a happy dude. However, for you folks that plan on trading before 100k, it is probably a non-issue.
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Nissan Titan Forums : Problems / Technical
Topic: K&N Filters May Harm Your Engine
