1994-2002 [Subscribe to Daily Digest] |
You will hear the turbo whine as it winds up, but that noise is transient, and you can hear a roar and rush... whoosh? When things are working right this is what happens. With the NG900's and 1999 9-3, the air boxes were very restrictive and also, by design, filtered out much of such noise. This older design presented many techical aspects that required modifications. The new designs are much much better and very little has to be done to improve intake flow.
K&N panel elements should not be ever swapped end for end when inspecting or servicing. The elements conform to the air box shape, which will not be perfectly symetrical with heat deformation. If you swap it end for end you may get air leaks past the filter suround that would not otherwise occur.
Filter charger? Not a drop in replacement element?
(Those who install cone filters that take in air under the hood experience net power reductions in warm and hot weather.)
There are those that will argue that with a T7 boost control system, that a K&N will have no advantage. Well, there is some merit to that argument, and I will not go into all of that logic. However, even with a T7 system, a reduction in flow restrictions leads to lower temperatures from the turbocompressor which promotes better ignition timing, and the turbine is worked harder as the compressor requires less speed and power. This means that the wastegate is further open, and the exhaust back pressure above the turbine is reduced, and this directly translates into greater shaft HP for the same T7 operating point. Lower temperatures also provide greater thermodynamic effiencies for the same T7 operating point as well. Note that with these types of turbo chargers, that the exhaust pressures developed to create 20 psi of boost, which the T7 can sometimes provide, will be in excess of 40 psi. The rule of thumb is around a 2:1 back pressure to boost pressure ratio. At high flow rates and in hot weather the turbine is operating in parts of its 'compressor map' where the efficiencies that are relatively poor and things can only get worse.
There are two realms of this. One is where the turbo is able to meet the T7 air flow and pressure demands and the wastegate is being used to modulate the wastegate. This is where the T7 arguements apply that the a K&N and other mods are argued to have no first order benefits. I outlined the second order benefits above. There is the second case where the air flows are so high, that the limits of the turbo chargers have been reached, and the wastegate is closed and the turbo is doing everything that it can do to product boost. The turbine is just too small. In this area of operation, the boost pressure is dropping off at high RPM. Some of this is created by pressure drops across the IC and some from the air filter. When such things occur, the IC and filter can be improved and first order power benefits will be had. As these things occur at high air flows which occur at high RPMs, the result is increase HP. So one can, under certain circimstances, see improved boost at higher RPMs. All of this is very theoretical and how this theory meets reality with these engines is something that I am unfamilar with. I have a T7 9-5 Aero and I am just starting to see what it can do as the engine wears in. With 5K it seems to be changing quite nicely. But with traction control and snow tires things are quite out of reach.
So thats the way that I see it. If anyone can refine or evolve my current understanding I will happy to learn more.
posted by 208.24.179...
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