Quieting down exhaust noise

[jasonrusso]

My club recently got thrown out of our old field for a single noise complaint which turned into a zoning infraction (using a farm for non-farming activities). Either way, we found a new field and some of the members are paranoid about noise now.
Anyway, I have 3 main helis I fly. I have a Trex 700n with a YS-91 SR. I have a Hatori pipe on that one. I have 2 600n. One has a YS-56 and the other has a OS 55HZ. Both have the respective Outrage pipes.
I haven't flown the OS for a while, but the 600 with the YS was measured at 91dB and the 700 was measured at 90dB.
Is there anything I can try that will lower the noise without robbing the power? A different pipe? After-muffler?

[ChapaWolf]

I had an outrage on my os 55, not only was it fricken noisey it sucked. The only way I know that, is when it fell apart I bought the OS Powerboost II and not only did it make half the noise it became easier to tune and produced serious power. Hopefully you will take my advice and buy the OS Powerboost, when it comes to pipes who knows better than the manufacturer. Plus I have a couple dents in mine and no sign of breakage. Plus the fastening is better than most with the outrage I couldn't keep it from rattling loose. With the OS I forgot about the troubles I used to have because I only put a wrench on it when I take it off or put it on.