My Custom Stainless Exhaust System.

[MSGGrunt]

After lots of research, questions and reading on all kinds of forums I finally bought all the pieces for a custom Stainless exhaust system on my 1987 M6 with M88 motor.

* I will be building a single 3" all T304 system from the header down pipes to the muffler.

* I will replace the stock down pipes off the header with 2.25" stainless dumping into a 2.25" to 3" Y-pipe. I can't find a T304 Y-pipe.

* Just before the Cat will be my O2 sensor.

* Off the Y-pipe will be a 3" Magnaflow Pre OBDII 3-way polished Catalytic converter from Jegs. Part No. 94309. $119.85 (T-409 SS)

* After the Cat will be a Vibrant Performance Ultra Quiet resonator from Jegs. Part No. 1142. $94.50

* The muffler will be a Vibrant Performance Streetpower muffler from Jegs. Part No. 1119. $94.50

* System will incorporate SS V-band clamps for easy of removal and all T304 mandrel bent tubing.

From the very beginning I knew I would not settle for anything less than T304 stainless. Though T409 is durable enough I wanted the shine that only the T304 can provide with no maintenance. This limited my choices and initially I was sold on buying a Borla muffler and initially an MBRP resonator as they are both made out of T304. I wanted a resonator and not add just another muffler or cherry bomb after the converter as from my research the two are designed to do two different things. The muffler to muffler sound as its name implies and a resonator to cancel out certain sounds waves.

MUFFLERS:
The job of the muffler is to lessen the sounds of the engine to an appropriate and acoustically pleasing level. How does it work? Technically, a muffler quiets the engine by reducing the sound pressure emitted. Factory mufflers are made to sound good, but are restricted by efficiency concerns, ease and cost of manufacturing, and of course sound level laws. For many enthusiasts, the stock mufflers are too conservative. Mufflers are engineered with multiple chambers that expand exhaust gases as they pass through. These chambers feature perforated tubes or baffles – maybe even both. Exhaust passes through these perforated holes and baffles, resulting in expansion. As the gas expands, its pressure lessens, and consequently so does the sound level. Furthermore, OEM mufflers are often packed or lined with materials (such as fiberglass) as a soundproofing measure to further absorb the sound inside the muffler and emit less ambient noise. All in all:

Muffles/lowers sound level
Usually packed with fiberglass
Does not eliminate certain frequencies of sound (droning)

RESONATORS:
The purpose of a resonator is to cancel out a certain range of sound frequencies. Without getting too scientific, sound is simply a pressure wave emitted at a certain frequency. Like waves in the ocean, sound waves have certain amplitudes (comparable to overall size), a crest and a trough. At the beach, when the crest of a wave meets the trough of wave of the same size, the two waves actually cancel each other out and there will no longer be any wave. The exact same principle applies to sounds waves. If you have two sound waves of the same size and frequency meet crest-to-trough, they too will cancel.

This begs the question, what range will be cancelled? Well, that's left up to the engineers. Typically an automotive sound engineer will choose a range that is not pleasant to hear and build the resonator to eliminate that frequency. Noises that are cancelled are harsh noises or ranges where the exhaust note produced would be a loud drone or irritating buzz.

So what does a resonator do for your BMW? A resonator makes your overall exhaust note louder and more aggressive. It's not quite a straight-pipe, but it isn’t too far off. Note that nowhere does it say that a resonator lessens sound. It only eliminates certain frequencies.

Almost straight pipe sound level
Cancels certain frequencies to stop droning and obnoxious noise
Not adjustable at all, you either like it or you do not

The MBRP resonator, though made out of T304, is sold by a company that caters to the diesel crowd and I was uncertain if these motors have different "annoying" frequencies that need to be cancelled out so I continued my search. What I found was a resonator built by Vibrant Performance that specifically talked about 6 and 8 cylinder gas engine and this is what I went with. They also sell mufflers and researching the difference between Vibrant and Borla was sound and more personal preference than anything. I did read that Borla is made in the USA where Vibrant is made in Taiwan but, each got great reviews for sound and quality of build. The Vibrant was also $45.00 cheaper. The cost savings was a very small issue but what did sway me was having a "system" (resonator and muffler) from the same manufacturer.

I will report what the custom install costs once I have a break in the New England weather to take my car to the shop.

I will make sure to get a sound bite for those interested in how loud or quiet my concoction turns out. Especially since most people stick with the twin pipe design and I'm going with a single 3" system.

More to follow.

[MSGGrunt]

An eye opening response from Vibrant Performance when I asked them what the difference was between their resonators and mufflers. I sent them this question after mine arrived and their was no discernable difference between the two other than size. And all my research lead me to believe that resonators were designed differently to reduce sound waves where a muffler reduces noise. Am I wrong and the exhaust companies are just selling a one application fits all be it a resonator or muffler?

http://vibrantperformance.com/catalog/i ... _1033_1055

Hi David,

All our resonators and mufflers are a straight through design to maximize flow. Traditionally, a resonator is smaller as they need to fit in a smaller envelope in the mid-pipe of an exhaust. I have taken many calls from customers who want to maximize the reduction in the db level of their exhaust and often I will recommend using a muffler in place of the resonator if space permits. The rule of thumb with exhaust components is that the larger the body of the resonator/muffler, the more effective it will be at reducing the db level.

If you have any other questions, please let me know.

Thank you for choosing Vibrant,

Aaron Weir

TECHNICAL SUPPORT

Vibrant Performance
310 Courtneypark Drive East
Mississauga, ON L5T 2S5

T: 905-564-2808 x254 F: 905-564-8653

E: [email protected]

www.vibrantperformance.com

[MSGGrunt]

I have received all of the pieces that I will be supplying to the guy who will be building my exhaust. Clearly there will be some additional tubing in between each component, V-band clamps, hangers and some sort of exhaust tip.

I wonder, given the relative, IMHO, small size of the resonator and muffler what kind of and level of sound I will end up with. Only one way to find out I guess.

[MSGGrunt]

Aside from the resonator being shorter and oval and the muffler being longer and round, they look like the are made identically on the insides.

Overall I am satisfied with the build quality of the Vibrant Performance products.

[Dan101smith]

What made you go for 3" pipe, out of interest?

I dropped my race car off for a new exhaust this morning, and the wisdom was that 2.5" is more than enough, unless you want it to be loud.

[MSGGrunt]

I based going with 3" off research and others experience... Others that went with a single vs emulating the factory dual exhaust with larger tubing.

Da_Hose gave me a lot of advice. Here is what his thoughts were/are and it sounds logical.

OEM exhaust for the M6 is dual 50mm (2") at the collector. A pair of 2" pipes has a total area of 2.78 square inches per pipe, for a total area of 5.56. A single 3" has an area of 6.51. That isn't a huge increase over stock. If you go with a single 2.5" pipe, it only has 4.45 square inches. That is a reduction of 20% from stock. The criticism of a 3" is that is reduces velocity due to the slightly larger volume. The criticism of 2.5" is that it's a restriction compared to stock, and the S38/M88 is a high revving engine that doesn't like restrictions in the exhaust flow.

I have the Euro M88 in my M6 so, I went with 3". I also liked the idea of a single vs dual exhaust as it consists of half the tubing, half the bends, half the welds, and half the V-band clamps and makes for, I hope anyways, a less expensive exhaust system.

I also bought 4 V-Band clamps to weld into the system to make putting it together and taking it apart much easier, especially if I find my current set-up too loud and have the need to add another resonator/muffler

[MSGGrunt]

Some of my reasoning came from this thread.

viewtopic.php?f=2&t=24489&hilit=single+vs+dual+exhaust

[JCS]

A single 3" exhaust pipe is fine.
But the rear view tips should be 2 pipes, to avoid looking like a RICER car, and retain the stock look!

[MSGGrunt]

I will have nothing short of twin exhaust tips. This is a signature look of the back of the E24 and I will retain it.

[wjtesquire]

I just redid the exhaust on my M635. I ran two inch pipes from the headers to a Billy Boat exhaust can. It sounded great except at idle where it was too loud. I tried an X pipe as close to the headers as I could get and now its perfect. At idle it is much quieter and the sound in the cabin while driving is significantly reduced. With the windows down it sounds lower and meaner. If you run twin pipes and its too loud, try an X pipe first.

[MSGGrunt]

It will be 2.25" off the headers into a Y pipe that dumps into a 3" Magnaflow catalytic converter then into a Vibrant Performance resonator/muffler back to another Vibrant Performance muffler at the rear of the car to twin exhaust tips. All 3" rear of the Y pipe.

[Dan101smith]

I went with this:





Trying to keep it quiet enough for track limits here.

[MSGGrunt]

I would imagine my using a Cat will make mine a bit quieter but, probably not a whole lot. I am fully aware that it may take some trial and error to get just the right sound, no or little drone, etc. Fortunately this car is not a daily driver and is only brought out on nice sunny, Summer days so I "may" be able to live with a louder exhaust note than I would on a daily driver.

[sansouci]

Does anyone add a layer of Dynamat to tune or attenuate the cabin noise if the piping is not quite what you wanted to achieve?

[Dan101smith]

I would imagine my using a Cat will make mine a bit quieter but, probably not a whole lot. I am fully aware that it may take some trial and error to get just the right sound, no or little drone, etc. Fortunately this car is not a daily driver and is only brought out on nice sunny, Summer days so I "may" be able to live with a louder exhaust note than I would on a daily driver.

Don't get me wrong, I've not actually heard mine run yet - it might sound awful!

[MSGGrunt]

I have heard great things about Dynamat. The only negative being added weight. Speaking of weight, I was amazed at how heavy some (the rear A/C side panels, door panel inserts, cooler top cover, rear passenger side panels) of the interior pieces weight. The A/C side panels and door panels inserts actually being made of out sheet Metal. I am used to the Mercedes where these are made out of fiberboard. The only thing "light" are the rear seats themselves.

[TBM]

Any updates on the exhaust work??

[Da_Hose]

Your setup is essentially what I run. Except I also have a Moroso Spiral flow inline and a Flowmaster DBX muffler. With your straight through setup, you will have a pretty brutal drone at 2500RPM or so, and you will be LOUD! It will sound like a friggin race car when you spool it up, and bark on decel.

Jose

[MSGGrunt]

This project kind of lost steam when I removed the rear muffler and added straight pipes from the converter back and was pretty happy with how the car sounds. That and I bought an E30 325i convertible that I have been doing some small projects on. I still have all of the pieces so, when I run out of other projects this one will be revisited.