Originally Posted by
JimmyXR6T04
It probably won't help you due to how much drone you have, but i laid dynamat throughout my boot as i had a bit of resonance at 2500rpm. It only lasted until about 2700rpm, but for that 200rpm the whole car vibrated, it was more a vibration/resonance/boom type sound. The dynamat toned it down heaps. So if there's still a bit of resonance when you fit j pipes, try some dynamat in the boot. Mine was really bad when the exhaust was first fitted, but then i realised i didn't have the spare in the boot. Put that back in, plus dynamat and the difference was huge. The massive open wheel well was the main cause of my drone/resonance. Obviously we're talking different cars here, but just pointing out some things that might help.
One thing to be mindful of; I hated the J pipes on my caprice. They hung down like dogs balls, looked ugly and scraped on bloody everything (even driving at 100km/h on a country road they'd hit and scrape). The LWB didn't help, but it was only lowered on SSL all round, which was equivalent to SSSL for a sedan. My front bar easily cleared gutters, and i had plenty of clearance, it was just the exhaust that hung so low. Hopefully they tuck up a bit better on the GTS.