Found this thread while searching for cures for exhaust drone. Gave it a try today and the results are better than I expected. I've got a 2010 NISMO with HFCs and Beluga axle backs. The goal was to reduce the drone between 2500 to 3000rpm. I had the muffler shop install a side branch resonator on each side just before the axle back flanges. Using the formula found in this thread, each branch length is 28in, using 2.25in pipe and capped at the ends. I'm very happy with the results, as the drone at the target rpm range has been reduced by about 80%, and the entire rpm range sounds smoother.
I'm sure others have done this as well as this thread is pretty old. I wasn't aware of this method and just wanted to report that it does work. I know that some aftermarket exhausts come with the resonators, but never thought of fabricating them on exhausts that didn't include them.
The job cost me $125 including parts and labor.
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