I have a custom exhaust that is just way to loud, IN THE CAR, for me to continue to consider long drives.

My system consists of a London Stainless Header with hi flow CAT a 2.5" SuperSprint connector pipe (no resonator) and two mandrel bent pipes from Burns Stainless, followed by a 17" SuperTrapp with a side rear exit. I am happy with the way it looks and sounds outside the car though I wouldn't mind it being a few db quieter.

How much difference will the SS resonator make? I just ordered it from ProMini. They said it was 5" in diameter which is good but it looks like it could be longer. It's going to take 4 weeks to get it though!

A friend taking, a similar approach on his exhaust, but with a JIC Bullet muffler said his resonator (not the SS) made very little difference and he has to use a silencer in the end of his bullet just to drive across town and that it kills the power. Some people say the same about the SuperTrapps, though Garfield gave it good reviews on his stock class MCS. I never got mine on the dyno.

I have also decided to replace the SuperTrapp. What looks like a no brainer is the Borla XR-1 Bullet with a 14" case. It looks like it is just the right size to replace the ST without any extra work. It has a perforated multi core interior, which is supposed be quieter than other straight through designs due to reflective technology, but it's only 3.5" in diameter so I'm wondering how good could it be? Looks like it will cost apx. $160 for the Bullet but they also have another XR-1 mulller #40941 for $126 I might be able to squeeze in. It's an oval with a 12" case, 2.5" in/out and 4.5" x 7.875" so it should have a lot more room for deadening but it's not one of their multi core designs that I can tell, so I'm kind of left to guess which is best. Anyone with experience on these?

4/19/06, Important Supertrapp info contained further down this thread!

 

I changed from w/o the resonator to their center pipe w/ resonator, and there is a difference. I'd say the db's were a tad less, and sound more refined...

I have a straight-through system with a Borla Turbo muffler, and the sound is very acceptable. You might be content with the simple addition of the center pipe w/ resonator...

 

Any chance you took sound level measurements? I'm hopeing to reduce sound levels at 3K by 6db or more.

 

Believe it or not, I did! Peter of M7 sent his sound pressure meter to me during my experimentation. I have a monster thread on MINI2, in their Performance forum... A key word search for "muffler of choice" should find it...

With that said, I don't believe I took readings with the SS center pipe, so you might not want to bother hunting it down...

If you don't mind going non-stainless steel, check-out the Moroso Spiralflow. This will fit in the tunnel, and should help as well...

 

WHAT???!!!

 

After thinking things through some more and calling Borla, I decided to order a XR-1 Bullet from Summit Racing and a light weight, stainless, racing muffler from Coast Fabrication (they make Burns mufflers) to use as a resonator and cancel my SS resonator order. They will make custom lenghts, are rebuildable and offer different sound deadening materials, depending on your needs. I went with their 4.5", (SuperSprint was 5") 17.1" standard lenght (total lenght) muffler and got the "scrub able interior". That means, the deadening material is STAINLESS and highly heat resistant. The way the guy described it, think stainless steel wool but instead of fine wire it's flat, maybe an 1/8" wide, and curley.

They had none in stock but would MAKE ME ONE on Monday!!!

While my car is in for the JCW kit I had the guy measure for the resonater and he said 18" max, was the available space. The Coast muffler is thin stainless and only has about 1/4" of pipe after the tapered rear end of the muffler so he recommended expanding the existing end of my pipe to slip over that and to weld it to the End Cap of the muffler, for added strength. The front end has a typical slip connection. My guess, I'll need to cut out about 15", of the existing pipe.

I may try to get a sound meter on all this, in stages.

 

I had a quick chance to put the Borla XR-1 Bullet on in place of my 17" SuperTrapp. It was a nice fit and we started the car without clamping the slip joint down, since it was such a good fit. It seemed to be louder than the Supertrapp so I took it off and put the Coast / Burns race muffler on. The Coast was clamped down as time was about up and I really didn't want to put the Supertrapp back on. This seems to be about as loud as the ST but with a slightly different sound, a little worse, and the loudest part of the rpm band was extended maybe another 200 rpm. The Coast will be moved to just behind the CAT, to be a resonator, as I intended from the start but I am somewhat surprised it wasn't quieter than the ST, as it has about 2.5 times the sound deadening material of the ST. I guess it's the straight through design and maybe the difference in deadening material.

Since the Borla seems to be out, I considered two Coast mufflers, maybe with a different deadening material for the rear, since heat would be less an issue but in checking Supertrapp options I found that their 5" disc version, besides being 1" bigger in diameter is apx. 2" longer and has apx. 2.7 times the sound deadenig material of the 4"x17" trapp. so I've ordered one of them. The 24" long, 4" trapp would fit at the rear but would require me to get two tighter bends, than I now have (45 & 15) and they would be right on top of each other, instead of the 12-14" I have now and the 24" Supertrapp has only apx. 1.6 times the sound deanening material of the 17". The 5"x19" trapp plus the Coast muffler will give me apx. a 523% increase in deadening area over just the 4"x17" Trapp.

I really think just having a resonator is the most important part of reducing mid-range drone, 3K +/- 300 rpm, from everything I've read here.

Other options, get Coast to build me a 19x5" muffler, with ceramic deadening material for the rear, instead of the Trapp or get them to build me a 24"x3.5" muffler for just before my 45 deg. bend and have 3 mufflers then. That, 3rd muffler, should certainly take resonance out of the equation and bring my deadening area up to 675+%.

I was not unhappy with the way my 4" trapp looked but think the 5" will look worse, the Coast certainly look's different at the end. Better or worse I'm undecided but probably better than the 5" Trapp will look.

I do, now, have a sound meter and will take numbers.

 

My new 543-2519, 5" disc, Supertrapp went on today and it works GREAT . I did some before and after sound level measurements, more tomorrow, and it looks like 3-6 db sound reduction depending on conditions but that's not the whole story. The sound quality is much better, no drone even without a resonator which I thought wouldn't be possible with my headers and 2.5" minimal bend system. I may change my mind but the Burns muffler, that was going to be my resonator, may never go on. I just don't think it's needed now.

The Burns weighed 3.56 lb. the 17"x4" disc Trapp was 4 lb. and the new 5" disc Trapp is 7 lb. but well worth it!

I did notice some oddities about the SuperTrapps. Well, these are Universal mufflers so maybe I should call them compromises. As I had some time on my hands until I could get to a lift, I decided to take the new Trapp apart and put high temp. anti-seize on everything that may ever have to come apart and just generally check out the design. The 5" disc trapp seems to be optimized for either a 3" or 3.5" core as there is an expanded space between the 2.5" inlet of mine and the 2.5" core of the sound deadening area. The space was mostly an even taper but had two steps. The length and width of this open, unmuffled area was 4"x apx. 3.5". I felt like this might compromise the performance (hp output), like a gutted CAT if the inlet pipe wasn't extended all the way to the sound deadening core, 6.5" from the actual begining of the muffler. Before taking it apart, I thought, I might have to take 2" off the existing pipe, since the new Trapp is 2" longer than the old but then I found I needed 4.5" more pipe, than I thought, to do the job I now thought needed doing. As, I just happened to have 2' of extra 2.5" stainless, I cut 4.5" off and stuffed it in the hole, to span the void, after first making sure everything lined up, then butted the old pipe into that. Of course, now my old pipe is 2" to long after all but it pretty much had to be done that way to span the void. 2" will come off the old pipe later.

It appears the 4" disc Trapps are optimized for a 2.5" core, so if you are thinking about putting one on a smaller diameter pipe you might want to consider spaning the void as well. This may even be part of the reason for the resonance I had, even though mine is 2.5". When in doubt span it.

Also odd, is the sound deadening core is the same length, for the 19" Trapp, as the 17". It's that damn tapered void on the 5" dics model, needed to make it fit 3 different core sizes. In the end, my sound deadening area only increased 100% over the 443-2517 Trapp I had but boy does it work!

As the number of discs affects noise levels and the effective open area of the muffler, I will point out that I went from 11, 4" discs, to 12, 5" discs, which by some of ST's techniical data, I figure, I now have 36-37% more open area and it's still quieter.

Good things, sometimes, come in slightly larger packages.

More sound level measurements, at idle, in car, windows and vent closed, dbC changed from 86 to 78. dbA changed from 64 to 58. Highway speeds 50-60 mph current dbA 75 with engine speeds from 2.6K to 3.2K and 90 dbC. At 70 mph in 5th and 6th, 77 dbA, 93 dbC. Vent open window cracked 6th gear, 81 dbA, 98 dbC at 70 mph.

 

So do I understand correctly that you didnt replace the SuperSprint center pipe without resonator? Sounds like you were going to operate on it but havent done that either? I'm only asking because I was hoping that you did replace the pipe so that you would want to sell the old one.

 

No, I was told it was going to take 4 weeks to get, so two days later I ordered the Burns/Coast racing muffler to use as a resonator. Of course when I called to cancel the Supersprint order a few days after that, it was already out for delivery. I just refused the order.

 

Well, here when I thought with the different hitch options for the MCS, now on the market, that no one would do another one sided SuperTrapp exhaust. It turns out that when OasisT (Craig Wilcox) made practice runs in my car at the Peru Tour he liked it so much that he has ordered all the parts to copy my system.

 

Well, after 14 years and 130,000 miles I Blew out the guts of my 5" disc SuperTrapp, Middle of 4th or 5th run, felt a slight loss of power, then POW! Needless to say much louder after that and the ride home was super annoying. It also seemed faster. It looked to me like a lot of the disc's were obstructed or closed up, maybe rust. I'll be buying another one on Monday.

Since my last post on this thread, I had upped the number of disc's to 20, while dyno testing shortly after starting this thread. Power was still going up a little, so I think I'll just start at 24 discs this time but boy have they gone up in price!

 

I totally forgot about Supertrapp’s. Any pics of it on your MINI?

i used to run one on my CRX in the late 80’s. Do you have the stainless endcap, or the machined aluminum cap with the logo?