The Theory
The theory here is, as you let more air to the combustion chambers
to mix with the fuel, you get more power, but the first point is
that under which conditions does the air flow and do performance
air filters really provide more air as it has been told?
Aerodynamics, or let?s call it air flow here, is so complicated so
you can never be sure that the replacement of your conventional air
filter with an open element filter (like K&N, Kingdragon or
Green) will provide more air flow to the intake system
In-Box Applications
Let's discuss in-box applications like replacing the stock filter
with a inbox K&N first, for those who want to apply that kind
of air filter mods. On a test which made with a test air box
measuring the flow resistance of air yielded the following
results:
(The number 100% states the maximum flow resistance to the air,
meaning the air is somehow obstructed maximum by the filter or the
air box itself while passing through the combustion chambers.
Numbers lower than 100 indicate that air flows more easily
relatively to the conditions represented with the number 100. It is
natural that the air will flow most easily if you detach the filter
and the airbox, thus the lower number is 37.5 meaning the least
resistance has exposed to the air.
stock box w/ filter 100 %
stock box w/ K&N 100 %
stock box w/o filter 100 %
modified airbox (trimmed) w/filter 62.5%
modified w/K&N 56 %
individual filters 44 %
manifold only 37.5%
This test has shown that changing the stock filter with an inbox
performance filter like K&N is useless unless you make some
mods to the airbox, but the most surprising result is that whether
it?s an original filter or a performance filter like K&N, if
you take one of these filters out and apply the test again with an
empty air-box, there is still the same resistance like there is a
filter inside. That?s really really hard to believe, but when you
remember the test made with manifold only, you see that air still
has a resistance of 37.5. So, that?s aerodynamics we talked before
which is so hard to understand, and it?s not a big surprise that an
airbox causes so much resistance.
It?s clear that changing the stock filter with an in-box
performance filter like K&N is useless unless you make some
mods to the airbox, and it?s clear that it?s not usual to drive
without filter and the box, so instead of modifying the box, why
don?t we use an open element cotton filter? We can get a result
between 37.5 (the manifold only) and 56 (modified airbox with
K&N).
Open Element Performance Air Filters
Normally, the air passing through the intake system is 21% oxygen
while nitrous oxide is 33%. We all know that nitrous oxide is a
power-boosting, complete and more expensive mod in tuning process,
and I hope we all agree on the performance of this mod. Nitro
increases the density of the oxygen in the air to 33% from 21%,
which is still quite close to the natural density. Do you believe
that a cotton performance filter can increase the density of the
oxygen? No.. So, the only fact about the open element performance
filters is that they only let some more air to pass through, and
the most important question is that how much horsepower do we get
from them?
Tests on dynamometers show that you will lose horsepower, not gain
it if you don?t find a way to duct cool air directly to the cone
filter. Unshielded cone filters (K&N or any other) were
reported to yield a net loss in horse power. The factory filter
pulls cool air from outside the engine compartment, while open cone
filters will pull warm air from the area behind the radiator. Warm
air is less dense than cold, so this can cost between 6-13 HP. Cone
filters like K&N and similars only raise the Hp's by 0-2 Hp's
on a normally aspirated engine, however, on turbocharged or
supercharged engines, the increase is somewhat higher like 8-10 HP,
according to the power and vol. of the engine.
Another issue on performance air filters is that they only affect
the top end, meaning close to redline. You can feel a power loss at
low revs. And one other is that the cotton filters let in
considerably more dirt (300-500% more) than stock. Filter allows
more dust and fine dirt particles into the engine, but general
consensus is that this should make no difference to engine
wear.
Filter Maintenance
To maintain good filtration performance, regular cleaning and
application of filter oil is necessary. Otherwise the performance
will be worse than the original. The cleaning period depends on
driving conditions but a 6 month period is acceptable for average
maintenance time. Maintenance exist of two sections: Cleaning and
oiling.. To clean the filter, pour some gasoline into something
like a large, PVC bottle, and dip the filter into the gasoline for
1-2 hours. Rinse the filter and let it dry. Re-oil the filter by
spraying the oil onto the inside surface. That?s all..
Result
To get HP to increase, you need cold air... hot air will decrease
HP. So find a way to isolate the filter. Use a special, large entry
box that will help suck the cold air from outside the engine
compartment, or cut the hood.
Change your driving characteristics. Change gear at slightly higher
revs, cause you will get power at high revs especially closer to
redline. (I?m sure you also do that in any case, at least for
hearing the sound
Clean and re-oil your filter periodically. Even if you don?t clean
the filter, just re-oil it so you can be sure that the fine
particles or dust can?t pass through the filtering element.
