GTi Jake I appreciate the time and effort you took to write and start the thread but you don't fully understand how exhaust flow, frequencies, resonances and the like work other than what a book or video might tell you. In the past I've built custom one off exhausts for cars to tune out or move up the drone to higher rpm or to cancel it as much as possible on Hondas, Mustangs, Subarus, Evo/DSM. Which are heavily known to drone, boom, or rasp. For the GTI I search companies like BBE, Borla, Corsa, APR, AWE TOURING on what they were making and see they have spent much time into producing these systems. Of these companies; BBE, Borla and Corsa being the ones using patented technology specific to resolving this issue.
Your approach and understanding of the UQ Vibrant resonator of being too small is wrong. I have used these and have gotten better results in some cases. It's not the size but the placement. You will not know where to place the resonator which takes hacking up your setup a few times to get the right location. The 18" you offer does nothing more or less than add weight over UQ does the same if not better because overall the canister is large in diameter and it doesn't slow the exhaust down due to being short.
Currently I have a 4" CATLESS downpipe with BBE catback. I have no drone, I do however have a high pitch cam phasing at 2800 to 3000rpm. My BBE resonator is stubbier than the vibrant you suggested to use but 2 times the diameter. My resonator is not straight thru as well. The 2 mufflers are not straight thru either. I have no loss of power and I so happen to make 345+whp/400+wtq on a Dynojet and 320whp/381wtq on a Mustang Dyno on a STOCK IS20 which is nothing short of amazing with such a restrictive cat-back you would say?
BBE puts perforated baffles in the resonator and both rear mufflers, quite possibly the most "restrictive" physically looking exhaust on the market. It's quieter around town and idle then the stock catback. If I would get rid of it, it would be in favor of the other 4 companies I mentioned due to wanting a lighter weight system in exchange for more dB.
