It probably wouldn't go above 10k rpms because it now needs a custom map in a PC3 to adjust for new airflow that the stock ECU can't deal with. I remember trying no airbox cover once on a 1987 Magna. Same exact thing happened. I figured it all out years later (yes, I reinstalled it right after my initial failed experiment!) when I got really interested in tuning and tweaking bikes. I'm guilty of doing a minor airbox mod, and cut a small rectangle INSIDE the intake snorkel. That's all I'm going to do, but I also have a PC3.
I also did airbox mods to later model Magnas, and they did nothing noticeable in the mid range up. Only airbox mod that did make a difference was one done to a VTX1800, and I ended up getting a real intake anyway...LOL!
- T.
He argued that it was his fuel line that was kinked... but I think he ended up getting a new airbox cover anyway and cut that 2nd one a bit less
My own personal and non-empirical opinion is that the airbox mod can only do some good to your bike if you use a PCIII with custom map (dyno).
I just find it hard to believe when someone says "I cut my airbox cover randomly and now my bike has so much more power across the band", that's all :rockon: