Tom said:
The K&N filters do help airflow but beware of overoiling the filter when you
clean it. The oil vapors will destroy your mass airflow sensor. Also, It
really shouldn't impact fuel economy because the fuel/air mixture is set by
the computer. If air flows in more easily through your filter, the computer
will still adjust to the same mixture. The K&N's are great for older cars
before computers but do nothing for newer models, IMHO.
Fuel economy isn't just a function if air/fuel ratio. It is also a
function of pumping loss. Pulling air past a restriction requires
energy and the energy comes from the fuel. A less restrictive intake
and/or exhaust will reduce pumping loss and in theory will increase fuel
efficiency. However, the restriction from a paper element filter is
extremely low to start with so the K&N advantage is very small. I'd be
very surprised if the difference in fuel economy is enough to even
detect without very sophisticated instrumentation. A K&N may flow
better when heavily loaded than will a paper element filter, but very
few street vehicles will clog a paper filter in even 50,000 miles. I
still have the original air filter on my 2003 Dodge minivan at 85,000
miles and it is barely dirty. Unless you drive off-road or on a lot of
dirt roads behind other vehicles, you simply don't pick up much dust.
Old cars had the intake inside the engine compartment behind the front
wheels and the turbulence in the engine compartment from normal airflow
and the big old metal fans would stir a lot of road dust up around the
engine where the intake snorkle would pick it up. Virtually all modern
vehicles have the air intake up high behind the grill with a plastic
duct carrying the air to the air filter and then the fuel injector.
Even on a dirt road, you don't get dust into the top of the grill unless
you are driving behind another vehicle or passing a steady stream of
vehicles going the other direction. This is very different from the
"old days" when the engine compartment intake would pick up dust from
your own vehicle, not just other vehicles.
Matt