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Originally Posted by ItsPeteReally
Thats true at anything less than full throttle. Most of the time the driver limits the air flowing into the engine by applying less than full throttle and any other limitation of the airflow into the engine goes unnoticed.
But there is always a pressure drop across the air filter which increases as the engine revs rise and the engine tries to consume more air. If all other effects are discounted, removing the filter will increase the airflow into the cylinders when the throttle is wide open.
But there are other effects, which makes the outcome much more difficult to predict: the most obvious one being a change in the resonant behaviour of the inlet tract, caused by the change in the effective length and the amount of resonant damping.
My best guess is that the resonant frequency of the inlet tract drops and becomes 'peakier' ...... but the only way to be sure is to actually measure the flow
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The after market, the word “market” is significant, relies on the fact that specific measurements are very difficult to establish and assumptions become the basis of argument.
Manufactures most certainly take into account full throttle performance. Media testing has a profound affect on sales. When assessing the issue the layman should observe and give thought to the relative area of the OEM filter enclosure, as compared to the area of the inlet tract.
Rather that guess in regard to the pros and cons, I can put forward practical evidence. I have some experience with production car road circuit racing, whereby the regulations required that the OEM or an exactly fitting filter of alternative manufacture, be used. I became aware that several competitors were cheating by modifying there filter elements.
As a result I carried out a simple test to establish if they were placing me at a disadvantage. During practice, I removed the filter from my car, (On this occasion a Subaru FF1). The result was no improvement in lap times, which had been established as absolute maximum performance. As a result I refrained from protesting against the opposition, leaving them in dreamland.
