In previous testing, which I don't believe I ever posted here, in my IS300 I found that there is actually MORE restriction created by the aFe filter for the IS300 (due probably to the construction of the filter - more on that in a later article if I can find the pictures).
The HKS air filter (foam) flowed -slightly- better, but by slightly better, I mean less than 0.1 inches of water better which is so little that it literally makes no difference at all. The K&N was a similar story to the aFe.
I don't care what your butt dyno says because frankly, it's the most deceptive thing on the planet and you can't feel a 1-2hp difference... no matter how good you are.
But there's worse news for the drop-in filter crowd. Unfortunately, as expected, they also filter a lot worse than the factory paper air filter. Over time, that means more wear on your engine. Enough to matter? Maybe not, though some foam filters are pretty awful and I can only imagine how bad those cheap eBay conic filters are.
The bottom line is, don't bother wasting money on a drop-in... the "every little bit counts" mentality will only result in wasted money and decreased reliability here. While there may be anecdotal evidence that these filters add power on a dyno, that's all it is...anecdotal evidence. 1-5 horsepower is well within the margin of error on a dyno. In other words, it's easy to have two runs back to back with a 1-5 horsepower difference...
Invest your money instead in a differential pressure meter and do the testing described in the "Intelligent Modifications" article, your money will go a lot further that way. I use factory air filters in my cars and I recommend you do the same.
Check the link for more information about the filter filtration test:
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