Drop-in Air Filters And Cais

ethan_in_seattle · October 21, 2007

Hi,

I've been trying to find factual data to compare different types of air filters and CAIs but I've been largely unsuccessful. Has anyone posted a performance comparison between different makes of CAIs using the stock air filter as a baseline? I was considering replacing the OEM paper style filter with a K&N. I don't see the value in a CAI, other than possibly a slightly more throaty sounding engine, and so I was curious if anyone had actually seen a dyno comparison between different intakes that might justify the added expense.

It seems all manufacturers of CAIs claim that their product will grant more power and better economy, but I've yet to see any numbers to support these claims. My suspicion is that a K&N replacement filter will do just the same, and perhaps better than most CAI systems on the market. My reasoning is this: manufacturers dedicate a great deal of effort towards optimizing an engine to achieve the best balance of power, economy, noise, cost, and emissions. The weakest link in the system appears to be the filter itself. I believe manufacturers continue to use paper style filters because they're cheaper and ensure reoccurring revenue. On the other hand, the stock air boxes are made of thermally insulative plastic that significantly reduces heat transfer to the incoming air and are designed to draw the air from directly ahead of the engine bay where the air is coolest. I've heard the argument that CAIs are designed to encourage laminar flow and that this increases the amount of air the engine can aspirate, but most intake tubes are large enough that the effects of turbulence near the boundary layer will have little impact upon the pressure drop through the pipe, particularly through such a short distance. Furthermore, turbulent air is a good thing in the intake because it helps to mix the air with the fuel more efficiently. The pressure drop across the filter greatly outweighs the frictional losses is the pipe so it makes sense that simply replacing the filter element with a less restrictive style of filter would provide the greatest overall value.

As I own a IS350, squeezing out another 1-2hp is not my primary goal; rather, I would first and foremost like to improve my fuel economy without sacrificing performance. I'm aware that there exists a plethora of anecdotal evidence to suggest that one or another CAI works well, but I want facts, not hearsay.