OK assuming my car is standard, why would I want
to fit the largest cone filter possible? Three reasons. 1. Increased
service intervals, the larger the air filter the greater capacity it
will have to hold dirt, therefore it will need cleaning less often.
2. Increased filtration, the larger the area of the air filter
surface, the slower the air will move through the filter medium. The
slower the air moves the easier it becomes for the filter to hold
the dust particles as the particles have less momentum when they hit
the filter. (Special car should be taken when cleaning an oversized
filter as the dirt will fall off the filter much easier that it
would with a small filter as the small filter would have sucked the
dirt into the filter medium with much more force and therefore the
dust will be more strongly attached to the filter). 3. Power.
Although an appropriately sized performance air filter, when new,
will provide all the air standard engine needs, over time, as it
holds more and more dust, the less air the filter can flow. This
restriction will hurt horsepower gradually over time and so slowly
you may not even notice until you clean or replace the filter. The
same effect will happen on a large performance air filter but as the
filter can flow so much more air than is needed it will take much
much longer for the dust to have even the smallest effect on flow
and when it does start to restrict flow, the reduction in power will
take much much longer. Filters designed to flow just the right
amount of air will start restricting flow from day one as there is
no spare air flow capacity built into the filter, whereas with a
large filter there is plenty of spare capacity.
OK if oversized air filters are so great why don’t the
performance air filter companies supply them as standard? It simply
comes down to price; the aftermarket performance air filter industry
is incredibly competitive. It may be hard for a manufacturer to
justify a substantially greater price than a competitor, especially
when the power benefits are hard to notice, especially when the
filter is new and it is even harder to quantify the extra filtration
capacity.
In conclusion, like with most things in life, bigger is better.
If you are looking for a filter that will flow all the air you need,
have superior filtration of dust and have a longer service life,
bordering on fit and forget, the biggest performance filter you can
physically fit to your car will always be the best. As we
highlighted in a separate test, performance cone filters should, if
possible, be shielded from the heat of the engine and exhaust
manifold. Click here for the StrikeEngine
performance filter heat shield test
which details the temperature reductions heat shields can have
on intake air temperatures and therefore power.