Stock Air Filter - RESTRICTED!!! Lose It, Replace It

I assume that was a CO analyzer? That experiment doesn't really say much about how filter conductance affect engine performance. These days, with close-loop feedback controls, the engine ECU will compensate for a lot of conditions, including restricted intake. A clogged up air filter will probably flow enough volume to work just fine at part throttle and lower RPMs. At WOT and high RPM, the reduced air flow effciency will hurt performance, but the ECU will likely meter fuel to match the lesser air flow, so as to keep air/fuel ratio optimum and emissions under control. Dyno will show lesser HP up top; exhaust gas analyzer will see much of any difference.

However, I do agree that it is unlikely that Honda would have spec'ed an underperforming air filter if a much better one can be had for not a lot more Yen.

 

even if the K&N doesn't add any power, i do like the sound, and the ease and cost of maintenance