Performance Intakes have several functions.
First and foremost, the function of an intake is to
filter out dust and particles from the air about to enter
the engine while impeding flow as little as possible.
Simple drop-in types like K&N and ITG Panel Filters allow
the owner to keep the factory airbox, and provide
superior filtration and flow. Performance differences
may or may not be noticeable with this simplistic setup.
An advantage to this setup is the renewable aspect
of the filter itself - with a simple filter recharge kit
that costs about $10, you wash, dry, and re-oil the filter
instead of buying a new one. One filter should last
the lifetime of the car with proper care.
A slightly more aggressive solution is to remove the entire
factory airbox and replace it with a large cylindrical-type
K&N Filter (or similar). This kind of setup keeps the filter
in the same basic position (safe from water and snow) while
providing superior filtration and MUCH better airflow. The
difference in power should be noticeable, as should the sound
of the engine (VR6 engines will sound noticeably deeper and more
throaty while 1.8t engines will have a more pronounced "whoosh"
noise when the diverter valve vents). These filters are usually also renewable
using a filter recharge kit. A notable downside to this setup
is the fact that it is sucking in hot air could decrease any gains
that you would get from better airflow, or worse could result
in less power than the stock airbox.
Cold-Air Intakes are a twist on this kind of setup and are a much
more aggressive solution to obtaining higher performance. The basic
idea is that an engine will produce more power when inhaling
cold air rather than hot air. These kits usually consist of a
large tube (hopefully made from non-heat-conducting material) running from the
intake down into the wheelwell, where the filter is placed. Here,
it can breathe in much cooler air compared to the solutions that
place the filter right next to the piping-hot engine. The sound
of the engine will change to about the same extent as listed above,
and power gains have been quoted in the 5-8 HP range.
Finally, there are hybrid type solutions that keep a high-quality
filter in the stock area, but use heat-shields and sometimes ducting
to draw cooler air into the intake. Power gain and sound difference
should be noticeable
It is generally agreed that cold-air intakes are the best solution
for high performance, BUT with that comes an inherent risk: water!
If you happen to live in an area where torrential rain and snowstorms
are commonplace, you may want to reconsider this type of solution, or look
into safeguards that will stop the water from getting to the engine
in the case that it is sucked through the filter (AEM makes something
along these lines).
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