82 dB at what distance?

If i were you id just do a throttle mix. The 140DZ is reasonably quiet in the air anyway so your noise man wont notice. Ive never heard a Weston muffler but to have to drop 4dB is asking quite a lot.

Plus that growl or roar you hear you get off all DZ's, even the new 160.

Angus

ps i found the 16.5X12W quite noisy. Its actually almost identical blade width to a 16X12 (16.5" APC props are much narrower than 16 inch), so your 16.5X12 is really a narrow blade prop, less load, more noise. Try the 17X12 first but not 17X13 as it will over load it. If its still over on a 17X12 then id just throttle mix it.