Specifically I'm looking for the most effective sound deadening device (muffler or Resonator} to go immediately behind the cat. To make it even more difficult, I want something that doesn't reduce ground clearance or horsepower.

I have heard good things for years about the Vibrant Ultra Quiet but one respected member said it didn't do anything for his Mini. My next thought was the Flowmaster Super HP 2, assuming it will fit but again another member, using at the rear (not where I'd want to put it} said it wasn't enough.

I currently have just a Supertrapp and that was fine until I had to rebuild it and I still have a couple of options with it but I'm thinking ahead. Has anyone had positive results, volume wise, with either the Vibrant Ultra Quiet, Super HP 2 or anything else?

 

I just had a “turbo” muffler installed in that spot on my R53 that’s not straight through. Bends a little inside.

The previous owner replaced the resonator and two rear mufflers with straight pipe on the JCW system.

so I’m running just that one muffler now and it eliminated most of the drone. It’s still there but overall so much lower.

Before, the exhaust would also snap crackle and pop a lot when you came off the gas. It does it still some, but more burble than a crack, if that makes sense.

But I’m mainly warning you that if your setup crackles and pops now, a resonator style muffler might really muffle that.

 

It has been my experience that Flowmasters are quite loud.

 

Flow master has a lot of different mufflers with different sound levels though.

 

Yes, & I still don't think any of them are quiet. That's why I made my own.

 

For a quality, quiet but nice sounding exhaust, resonated miltek is probably one of the best.

I used to sell them for Audi, Porsche, and vw. Almost too quiet, but they have the non-resonated for louder of course.

 

And the Jpipe method is something I’ll probably look at in the future for drone elimination

 

Those work, but to be most effective, they need to be sized correctly. You can't just stick some extra pipe on there and call it a day. That's because they work like blowing across a beer bottle - different volume, different tone. The sound pressure that's created from those tubes cancels out the sounds in the exhaust that you don't want.

I would love to do a 3" single exhaust on my Clubman with a Helmholtz chamber on the unused side.

 

Update. The Supertrapp is sufficiently quiet now. My exhaust pipe is not long enough to butt up against the internal core of the Trapp and in the past I had put a 4.5" section of 2.5" pipe inside the Trapp to span the internal gap and thought that might have made the difference between the 4" diameter Trapp I used to have and the newer 5" ones, despite the fact that I went from 12? discs in the 4 to 18 discs in the 5, which should have made it much louder but was actually quieter. At the same time I put the 4.5" pipe in I decided to take two disc's out, just in case it wasn't enough. Well that wasn't necessary and I've put the two discs back in and it hardly makes a noise difference, may be 2db. I had previously measured the difference between my 4" and 5" at least 6db, depending on the driving situation. I think maybe I had had the same problem with the 4" but just never realized it but it just could have been the fact that the 5" has 2x as much sound deadening material inside.

I still think about the possibility of a light weight dual exhaust, maybe with a round 5" muffler at the end of both pipes but I doubt anything, short of a full Titanium system is as light as what I have and even then it would probably not be a dual exhaust.

So, while I would not call my system quiet, it's quiet enough now to not drive me crazy or cause permanent hearing loss and it probably won't get me pulled by the police. If for some reason you are considering a SuperTrapp. I highly recommend that you butt your exhaust pipe up to the internal core of the Trapp. My previous one lasted somewhere between 80 an 100K miles, so I don't think I'll be needing another one, on this car anyway.

Side note, while the car was on the lift, i measured the space I thought I could put a muffler or resonator after the cat and came up with a 5" round with a body length of 14-15". Again. the Vibrant Ultra Quiet gets good ratings from most, is reputed to fit and is something like 4.75 x 6.5 x 13?