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Of course, K&N filters come with a “million mile warranty”, so another option would be to gripe to K&N about the
problem.
For some of us, performance is not the issue with air filters; the wear rate of an engine can be closely related to the
filtration of the air intake, and any risk of inferior filtration would not be worthwhile. K&N claims that a NASCAR
stock car fitted with its filters will outperform a car with no filters over a 500-mile event, since the deterioration of the
engine due to contaminated air over 500 miles will exceed the power loss due to the intake restriction of a K&N filter.
K&N claims excellent filtration -- although there have been some contradictory reports from other sources. K&N
filters contain a layer of cotton soaked with sticky oil; as the air passes through the cotton, particles should stick to the
oil. Such a system normally is not described as a particular size micron filter, since it really should stop all particles
regardless of size. The stock paper filter, on the other hand, is a porous media filter, and particles below a certain size
are free to pass right through.
Either K&N or the stock paper filter is probably acceptable from a filtration standpoint. However, speaking as an
engineer, I must express doubts about the filtration efficiency of most of the foam filters I have seen (I haven’t seen the
AJ6 Engineering foam filters). A foam filter works on a similar theory as the K&N, the foam providing a media for the
air to pass through that is coated with sticky oil. However, the passages between the cotton fibers on a K&N filter are
very tiny indeed, it’s hard to imagine how a speck of dust could get through without sticking, but some foam filters you
can see through. And even some of those you can’t see through appear to have passages that are quite large. And I’ve
also seen foam deteriorate, with crumbs of foam breaking off and going into the inlet. And even if the chunks of foam
don’t harm the engine, note that each chunk leaving leaves an opening for more dirt to pass through the filter
unimpeded.
OPENING UP THE AIR INTAKES: Each of the air cleaner housings has a long tapered tube with a relatively small
opening for the air intake. The purpose of the small intake opening is to accelerate the air to near Mach 1 at wide open
throttle. This prevents intake sound from coming forward through the intake. In other words, it makes the car quiet.
Unfortunately, the air is now moving fast, and there’s an air filter up ahead. If the air is allowed to simply run into the
filter, the energy associated with the speed will be wasted, and the result is a loss of pressure. Therefore, Jaguar
provides the tapered tube to gradually and efficiently slow the air down, recovering most of the energy and pressure.
Jaguar designed this tapered tube as long as they could fit under the hood.
Also unfortunately, once the air reaches Mach 1, the passage is “choked” and all the sucking the engine can manage
will not increase the amount of air flowing through it. The opening therefore forms an absolute control on the
maximum amount of air going into the engine -- and therefore the HP generated.
If you cut off this intake tube and form a large opening for the air intake into the air cleaner housing, you will eliminate
this restriction. If you interfere with the mounting of the temperature sensor in the left side intake tube, relocate it into
the housing itself (drill a hole and use a nut on the inside); it can sense the air temperature anywhere in there. Because
the EFI system detects manifold vacuum, the system will automatically compensate for the increased airflow; no tuning
modifications are required. There is no effect on emissions, so there should be no complaints from inspectors.
At part throttle (most of the time with an engine this powerful), the butterfly acts as an air-accelerating restriction, and
no sound gets out anyway. The car will sound like it did before. However, when you open it up, you will be greeted
with a sonorous growl from under the hood. This is a very sexy sound, but some Jag owners may not like it.
The performance improvement goes along with the noise. In any situation where there is still no sound, there is no
change in performance either. When the engine growls, there is more airflow than there was before.
This mod will have no effect on fuel economy, except when you hear the growl; at that point, increased fuel use
accompanies the increased airflow and increased power.
You can give this mod a trial run without much effort. Unscrew the air temperature sensor, then reconnect the wire to it
and tape it down anywhere convenient. Then, remove both air filter covers and tie the air filters in place with some
wire. This setup will provide the same performance (and a little more noise) than the intake tube removal described
above.