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The Boxster's unique location for the intake may have an effect on HP losses or gains many have claimed. Unlike a front engined vehicle where the intake system can take advantage of the high pressure area naturally provided by forward motion, the Boxster's side mounted opening creates a low pressure at the intake opening as the vehicle moves forward. I suspect the snorkel places the intake opening at a point closer to the moving air than if the snorkel is removed. This would force more air into the intake system than with the snorkel removed. You can feel this effect easily by driving your car at 60 MPH and opening the window slightly. There is an immediate drop in pressure that you can feel in your ears. The area behind the grill feels the same drop in pressure. The higher pressure that exists at the opening of the intake dictates how much air is ingested into the engine. The odd shape of the intake area, with the snorkel removed, may cause areas of low pressure due to Bernoulli Effect of the moving fluid past the opening providing less air pressure at the intake opening. For this reason, it is possible the engine is getting less air with the snorkel removed.
I read the tuner's thread about the 17 runs he did, and on a stationary vehicle his claims may be correct but may not be correct on a moving vehicle due to the unique nature of the intake opening. A desnorkeled Boxster with a scoop on the side may give better results.
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