I’ve been seeing lots of discussion about induction air filters; foam filters, paper filters, and now Challenger (K&N) filters. What did my plane come with? How do they differ? Which one is best?
Technical Editor:
Complicated question. For starters, to my knowledge all of our Aero Center aircraft came from the factory with a pleated paper air filter. These filters resemble the traditional auto engine filter; some have an aluminum housing that encapsulates the filter element material. For this type, a factory replacement filter includes the one-piece unit; housing and all (and they are relatively expensive). They reportedly can be cleaned and reused, but I know of no one who takes that risk. If the filter gets damaged or loses structural integrity, it can be ingested into the engine. That seems to be to be an unreasonable risk to take for the price of an air filter, even if it is over-priced.
Most factory filters have long since been replaced by the Brackett system. This system provides a housing plus replaceable oiled-foam filter elements. These elements are not washable/reusable. They must be replaced. Replacement is seldom an issue due to the relatively low cost of the replaceable elements.
The new Challenger filter system is based on the K&N filters of automotive and racing fame. Instrumented tests show that these filters flow more air than the more common foam and pleated paper elements. While they are initially expensive, they are specifically designed to be cleaned, re-treated, and reused many times. As with most new products, they have a long list of favorable testimonials. I would love to hear from someone who has compared a new Challenger to the factory paper or the Brackett foam system, in one of our Aero Center aircraft.
For years rumor has had it that the factory paper filter results in more manifold pressure as compared with the Brackett foam filter. Bob S has also posted this opinion on the MM List. In my case, I had heard this from other mechanics, but always in the context of Bonanza applications. Sometimes I wonder whether these were instances of replacing a clogged Brackett filter element with a new Beech filter. It’s hard for me to believe that the FAA would have given Brackett (and now Challenger) their STC or PMA blessing, if the Bracketts and Challengers could not provide the same airflow as the factory filters. I have personally compared the factory paper filter to the foam Brackett filter, in my 1977 Sierra (IO360 200 HP), comparing new to new. In my case, the Brackett filter provided an extra half-inch of manifold pressure; contrary to most reports. Hopefully I will hear from someone on their results with the new Challenger; they do not yet offer one for the Aero Center IO360 applications.