So, hacking the stock air box appears to have done very little besides increase the intake noise slightly. A click or two up on the volume of the radio takes care of that in street driving. It was time to test out the other theory of removing the air box lid completely. I went back out to my secret test location, did two pulls with the lid on, stopped, took the lid off with the car still running, and did two more pulls all within a few minute span. Taking the lid off with the car still running made it easily apparent the car was going to be quite a bit louder. At WOT, it sounded like S2000s equipped with K&N intakes, but a bit louder.
What was the culprit for the power reduction? The hot air coming off the radiator caused drastically higher intake manifold air temperatures. The points I have tagged are at 7800rpm at the end of the first pull. Lid on versus off, the IAT was 131F vs 144F. Ignition timing was 25deg vs 24deg. Check out the ignition timing curves however and you can see with the lid on, the timing was running much higher through the entire pull. Looking through the complete plots and the second pulls, you can see the trends are consistent.
So, one lesson learned is Honda did a damn good job on optimizing the stock air box design and there’s nothing to be gained in power by hacking it up. The other lesson is colder is better (as should be obvious). Removing the air box lid will make your car much louder making everyone look at you. Removing the lid will also reduce your power significantly giving everyone more time to look at you. If you crave attention, I guess remove the lid. If you like more power and not drawing attention leave the lid on.