rodybmw

Let's assume that you have replaced your muffler with an aftermarket one and are very happy with the sound. However, you want to experiment and see how it would sound if it was just A LITTLE BIT louder.......which resonator(s) would you remove to add the LEAST amount of sound AND the least amount of droning (hopefully no droning/resonance at all)? Would you remove the two individual tube resonators up front, or the combined box resonator in the middle? This question does not apply to my car (yet), but I thought I would post it and see what you guys think. I heard the new exhaust of one of the members here and loved the fact that it was just a bit louder than stock and there was no resonance/droning........it's what I've been looking for since 2 or 3 years ago. He likes it the way it is (civilized, relatively quiet, deep sound, and no droning), but was curious what would make it just a little bit louder, and also be reversible if he didn't like it. I'm sure he will join in on the discussion in this thread too.

vegastrashed

Hey Rody,
When I put the RDSport quad exhaust on the 545i, the center box resonator was removed and replaced with a x-pipe. I found this to be too quiet and then had the two tube resonators removed. So, when I took you for a drive it was without the three resonators. I think you'll be happy with just the center resonator removed.

Bimmer32

Here's the true anatomy of the 545i/550i stock exhaust system:

The front 2 resonators straight through preforated pipes with fiberglass filled. Their aborbers by nature, so they do little to lower the noise or restriction of airflow.

The center resonator is basically 2 straight perforated pipes with also with fiberglass filled. The are like the above resonators except that it does a better job of absorbing the low frequencies associated with droning.

Then you have the two mufflers which only one is active while the smaller one comes alive with increase engine load (reving).

So in general, the 3 resonators do a good job of absorbing the low frequencies associated with droning while the muffler in the back quiets the noise further. Hence, stock exhaust are quiet and when the second muffler opens up, it sound tamed but sweet growl. I don't know the true anatomy of the stock mufflers, so I don't know its efficacy in sound/pressure management. As for back pressure, I'm not sure where the back pressure occurs on the stock exhaust system - maybe at the rear mufflers.

VT's x-pipe helps to balance out the engine pulses and "some" noise silicensing, but I don't know at what frequency. He's rear muffler are oval shaped, and might not be straight through pipes but tube and chamber filled with fiberglass. This type of muffler/resonator are most effective in noise silicensing, but because he has no resonators up front, it probably produce a sweet growl in the back. It's all about sound/pressure engineering and tunning.

Now, here's my theory based on what I have read and done:

Silence the low frequencies up front with tuned resonators/mufflers (tube and chamber and/or x-pipe combo) to minimize droning in the cabin, letting the higher frequencies flow to the back. Then take out the mufflers in the rear and put in resonators (straight through perforated pipes wrapped in fiberglass (glasspack), or cherry bombs. Then you'll get a nice growl that's louder than stock. Check out the sound clips on my Quad Monster threads.

KnIgHtCoM

I still have that discount available to me from RDSport if you're interested Rody.

jet190rs

JDN (RIP) always said that taking the center resonator out produces a drone while not making the exhaust any louder or sound better
http://forums.e60.net/index.php?s=&sho...st&p=122523
http://forums.e60.net/index.php?s=&sho...st&p=137121
http://forums.e60.net/index.php?s=&sho...st&p=169959

this member removed the front 2 resonators and he liked it -
http://forums.e60.net/index.php?showtopic=...mp;hl=resonator

Bimmer32

Those are good finds, jet190rs. Now if someone could tell me the anatomy of the rear stock mufflers, that would help to know for 545i / 550i stock exhaust system more (besides the cats and headers of course). If only I found JDN's post before, I probably would not have removed mine in the first place.

newbiebimmer

Rody was talking about my post here

http://forums.e60.net/index.php?showtopic=...st&p=498027

It was a long saga, but I finally go the Quad Remus, and it's sweet. I love starting it up, and driving with the windows down, stomping on the gas.. It's just a tad quieter than I think I expected. But the plus is that there's no droning..

Hence this post. Any first hand experience would be great..