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The K&N reduces the pressure drop in the system. Your MPGs are a part throttle operation and there is a huge pressure drop across the TB at steady speeds. The turbo is then not on boost. Any reduction of pressure drop across the filter will simply lead to the throttle plate being slightly more closed. So there is no effect on MPGs, and claims to the contrary on TV from autozone are totally misleading. That would only be true for some vehicles running with carbs and no O2 sensors. There are not many of those left on the road.
The benefit of a lower restriction air filter is some reduction in boost delay and higher torque at high RPMs. There is no real expectation of any improvement until you have Wide Open Throttle (WOT).
You have a T7, and the system already controls the air flow, so a lower restriction air filter does not lead to higher air and fuel flows as with the T5. But the turbo charger then needs to work less hard to generate the boost to get the ECUs target air flows. The turbine then has to produce less turbo shaft HP and the wastegate then is more open which reduces the turbine back pressure in the exhaust manifold. This directly translates into increased engine HP. This is the major secondary effect in a T7, there are others that I could describe.
A typical gas engine turbo application at 15 PSI of boost can be expected to have around 30 PSI of turbine back pressure. The boost energy is definately not free. But the 15 PSI of boost does deliver some power to the pistons during the intake stroke. So the thing that you are concerned with is the pressure difference relative to the boost pressure. So in this example, there is 15 PSI working against you.
Reduction of intake and exhaust pressure drops also serve to keep combustion chamber temps and exhaust vavle temps under control. In many tuned applications, high tempteratures are the limiting factor to engine survival. So power is one thing, and meltdown or valve buring is another.
, Wed, 27 Apr 2005 20:58:35
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