Let's get back to booming V6 exhausts.

[edwardmk]

Originally Posted by Lord of Hog

This is rapidly becoming the bane of my life entailing many hours underneath my X-plate 2.5 cursing the exhaust, the car and life in general.

The factory fitted rear box disintegrated at around 90k and I've spent the last 12000 miles fitting and removing a succession of replacement boxes all of which produced a loud resonating boom between 1200 and 2400 revs, louder than the engine in many cases which is a shame when the engine sounds so nice.

I've tried fitting additional soundproofing to the boot and that has improved things a little but I'd love to have some suggestions as to how to fix it.

Is it resonance in the boot/rear bumper area?
Is it the result of the pipes being too short and the bumper magnifying the sound?
Are the hangers too short (and if so how to fit longer ones while avoiding the pipe-knocking-on-the-crossmember sound)?

To be quite honest I'm running out of ideas so any suggestions would be gratefully accepted.

I have exactly the same resonance issue. My ZT-T was fitted with a very nice s/s Cybox cat back exhaust by the previous owner which resonated too much for us, so I had a local garage which specialises in S/S exhausts look at it. They recommended to remove it and go back to standard, which I did. The reduction was unfortunately not that significant. (I don't know what they fitted to be fair, but it was nice and shiny). Their comment was it was the correct system and should quieten down after a few hundred miles lol.
I still have the as new s/s Cybox system, but am now actively looking for the source of the resonance. I think the problem is the wheel well, which is resonating badly at 1400-2200 revs under load. The exhaust bracket on mine is welded to the passenger side of the wheel well, and even with a new rubber support, I feel it's not decoupling the exhaust enough from the side of the wheel well. With everything out of the wheel bay, tapping it really does boom like a steel drum. Play from engine mountings may also be another factor. but I haven't properly checked them yet. I'm going to clean up and paint the wheel well properly and then strategically supplement the existing sound deadener strips with Noico 2mm butyl sound deadener. I've a load of other stuff ongoing, so won't be able to report on results for a while until the car is back on the road.