With credit to Mike Dawson:
I contacted Challenger after reading the posting on BAC site and not seeing the C23 listed as STC’ed filters. They have emailed me that they do have a approved filter for the C-23. I am considering getting one but would like to here more coments from the group. I currently have the Brackett foam filter. I understand that the Challenger is a direct replacement. Has anyone tried this filter?
With credit to John Amundsen:
Challenger air filters are actually K&N air filters. Since I have just learned that these are now approved for our aircraft I will be ordering one for my Sundowner. I have one on my Ford diesel and have found it to be superior in maintenance costs to paper or foam. My son, who is an IA, has advised me that it is similar in performance to the paper filter and 2 to 3 percent better than the Bracket filter.
Comment from Mike Rellihan:
Having heard for so long that the Beech paper filters provided more manifold pressure than the Brackett foam filters, last year I had the opportunity to perform a back-to-back test. A good friend gave me a new Beech paper filter for my Sierra. My testing, performed at 7,500 feet with wide open throttle and 2,500 RPM, showed that the paper filter actually reduced my MP by one-half inch. I switched back to the Brackett foam filter, and regained the one-half inch of MP. This experiment made me wonder whether the reports of higher MP with the paper filter are due to swapping out a clogged Brackett element for a new paper filter, or whether it is related to the Bonanza/Baron application (where most of the reports originate). It clearly did not hold true for my Sierra.
In addition to the reduction in MP, the paper filter resulted in reduced cowling clearance. You would have to pretty much have brand-new engine mount cushions, to prevent cowling contact during start-up and shut-down, on the IO360-200 HP.
While Challenger/K&N did not show Sierra filters when I last looked, I would be very interested in hearing of anyone’s experience with them, on any engine. The instrumented tests I have seen in the past on them have shown definite airflow improvement over paper applications.
As another aspect of interest, I have a strong suspicion that the factory inlet air box on the IO360 in the Sierra is very marginal in cross-section area. While the engine only turns 2,700 RPM, which certainly reduces the airflow compared to an auto engine at twice that speed or more, the IO360 is operating at wide open throttle most of the time that it is above 8,000′ (or it should be!). The air filter area, whether foam or paper element, is a fraction of the size of an auto filter on an engine with half the displacement. Makes me wonder why the airframe engineers (the inlet is an airframe design, not an engine design), seem to think that aircraft engines only need half the induction filter area, versus what an auto engine designer determines.