2007 G35 VQ35HR 5AT.
I decided to upgrade my Y-Pipe back exhaust from that crappy 1.5" to 2.5" with a pipe kit from eBay. Pipe kit cost me $80, the passthrough resonators from ebay were $60 pair, the hangers i reused and bought 2 new hangers for the resonators cans and 2 new 2.5" band clamps.
At first install, the car sounded nice and bassy on idle, like a V8 but after giving it some gas, it started to sound like sht! Like a cat-less mustang begging for a muffler!
There was a serious drone, i mean, brain rattling drone between 2k-3k rpm in the range of 120-140Hz.

I've researched dozens of forums, youtube videos and found 1/4 wave resonator pipes (J-Pipes) and Helmholtz resonators. I tried the J-pipes but it was a total waste of time!
I decided to go with Helmholtz unit but there are so many calculators online that i just couldn't figure this out! Until i found this MR2 blog online about Drone Reduction and i was
VERY sceptical about it at first but after looking at my mushy brain from this drone, i decided to pull the trigger. I made a video, take a look, it's worth every bit of it!