Bimmer32

On non M 5 series, BMW didn't designed for end users to setup mufflers on both sides of the car for quad exhaust setup. Hence, we have to retrofit or purchase a tuned system to fit into the 5 inch width between the spare tire compartment and the battery housing. I've seen 4 x9 mufflers laid vertically, but you sacrifice the look of a muffler hanging out pass the bumper ground clearance level.

I thought I was clever to go with round 4" mufflers which did achieve the "no muffler" appearance. The sound is awesome with these glasspacks, but there were drawbacks.

Attack of the droning . . .

You see, I have reinstalled all 3 factory resonators (2 small preforated straight through and 1 boxed resonator - preforated straight thoughs), installed an x-pipe, and replaced 2 stock baffled mufflers with 2 glasspacks. The sound is sweet, and the sound level above 2K rpm is about 5 db above the stock sound. BUT, during deceleration (no engine load) or acceleration (straining engine load) around 1500 to 2000 rpm and idle at 750 rpm, the exhaust pressure isn't strong enough to push the air particles fast enough out of the exhaust system. Hence, the "sound waves" bombard the walls of the piping and thereby cause DRONING or resonance. Apparently, my search on other V8 forums identified that this is a "popular" problem with V8s. Additionally, idle sound is notably louder at 750 rpm versus 500 rpm.

BMW got around this droning or resonace problem with their stock exhaust by installing a springed switch valve at the end of the second muffler and using 2 baffled mufflers (compared to my glasspacks). Additionally, the path to the second muffler acts as a side resonator. Hence, under low engine load, the V8 exhaust has 5 resonators/mufflers, that is 2 fronts, 1 center, 1 rear, and the second muffler (as a side resonator when valve is closed). Since the exhaust air is traveling through a smaller (volume) path (compared to my twin 2.25 inches)and going out of a baffled muffler (compared to my glasspacks), there is little or no droning at low rpm because the air is more dense packed and less space to bombard around. At higher engine load (higher rpm), the springed valve opens . . . hence, you hear a nice tamed growl because the second muffler is now being used (opened).

So, what's the fix for droning when going with aftermarket exhaust? Spend money and get complete "tuned" headers and exhaust system or engineer a custom exhaust to get the SOUND and LOOK. Since there where no "tuned" system on the market that had the "look" I was looking for, I went with the second option.

To fix the droning or resonance and still keep the "no muffler appearance below rear bumper ground clearance level," I'm proposing to (in any combination):

1. Wrap the glasspacks in SS mesh or fiberglass (might not be practical)
2. Insert custom made reducers in the exhaust tips (creating silencers effect)
3. Find prefab. dual resonated tips (anyone found any?)
4. Reduce piping size after the center boxed resonator from 2.25 in to 2 inches
5. Quit, save the grief, and go back to stock and add a fake exhaust tip on the right side

What do you guys/gals think?

Bad Bimr

Do the above utilizing an electric cutout for the right side tips and have both quiet and loud at the touch of a switch.

BP

JPJ

I was going to suggest a similar approach of somehow adapting the OE flapper valve into the right side path.

Bimmer32

I was thinking about the same thing - to retrofit the OE spring loaded flapper the right side. The only challenge is that each header has itsown path to the glasspacks and only cross at the x-pipe where as in the OE, the mufflers and flapper was fed by one big pipe to two mufflers. Should I place the flapper after the x-pipe (hope there's room) or after the center resonator? I'll be butchering the OE system even more. I hope I'm targeting the right source of the drone.

JPJ

I'm thinking you could do it anywhere after the x-pipe/cross over. Could you try plugging up the right side (just at the tips) to see if there is still droning? If not you know this will fix it and then with the valve it would open when you needed more flow.

Bimmer32

Thanks, JPJ. I'll also try steel wool. Just hope I don't shoot a glowing hot ball on someone behind me. I think the location of the valve is important, but if someone can chime in with some advise, that would be great.

rodybmw

I installed a B&B muffler on my 545 a few years ago and after a month or so I couldn't take the droning anymore, so I put the stock muffler back on. Since then I have been looking for local members who have installed different exhausts on their cars so that I could take a ride in their cars and see if there are any that don't drone. In the last few months I've been bitten by the quad bug and have stepped up my research. Here's what I've found out:

-Custom quad Bolas w/ X-Pipe and no resonators.......moderate droning.....not as bad as my old B&B's, but still significant enough for me to take it off my list of possible candidates.

-Custom quad Magnaflows......did not take a ride in the car but the owner said that it has a lot of droning.

-RDSport full quad exhaust with X-Pipe. Joe (VT) let me ride in his old 545 and I did not hear any droning. I was in the car for only a couple of minutes and did not hear any droning, but I suppose it may have had droning under certain driving conditions that we didn't go through, but Joe said that it did not, and I don't think that it would have. The thing that rules out the RDSport for me is mainly the price.

-Remus quad system for the 525/530.......I heard this on both an Inline 6 and a V8. The inline 6 had all resonators removed and there was some droning, but much less than other systems that I had heard. The V8 still had all the resonators on the car and I did not hear any resonance/droning at all. That in addition to the deep "civilized" sound that was slightly louder than the stock has made this Remus my favorite system as of now.

A couple of things that I found out while I was researching the different setups:

-I called Manaflow and asked their tech support guy what he would recommend for no droning or least amount of droning. He just said that ALL their mufflers will drone because they are performance mufflers. I then specifically asked about one of their "XL 3-chamber mufflers" that they specifically market as one that would "reduce unwanted resonance" and he said that particular one would have the most droning because the gas would be bouncing off the front and rear walls of the muffler . That did not make sense as this was supposedly designed according to their own words on their website to "reduce unwanted resonance"....I am not convinced that he knew what he was talking about.

-I also called Borla and talked to their tech and he said to use the biggest muffler that I could fit in order to minimize the chance of droning and only have a 30% louder sound vs. the stock. He recommended their Borla Turbo XL.

By the way, both Borla and Magnaflow have ovals that would fit in the 5" space and they both have "offset" mufflers which have the outlet pipe at one end of the oval instead of the center of the oval. If you install the muffler so that that end is at the bottom then the muffler won't hang below the bumper level any more than a standard muffler on the left side.

So at this point personally I think the Remus quad for the I6's is the best setup for me. I heard it on Peter's (Newbiebimmer's) car and I have ordered one for my car too, although it will take a few weeks to get it in and installed.

Bimmer32

Thanks, Rodybmw, for the detail post. Today, I went to Lowes Hardware and bought a pack of 16 steel wool (used for paint removal application) for about $4.00. I stuffed 4 rolls in the tips (1 in each of the 4 tips), and MAGIC. Droning, COMPLETELY GONE. It had a nice growl below the 2000 rpm that I could hear from the rear, and I could even hear the radio on very low volume. The exhaust note did not change, just the sound level down and NO DRONE or RESONANCE. The sound is noticably louder than stock, but not too loud for a conservative guy like me civilized with a touch of aggressiveness.

Now, I just have to figure how to keep the wool in there.

rodybmw

Interesting.........aren't the steel wools blocking the exhaust path? Are they not restricting the flow?

Bad Bimr

I was thinking the same thing. Exhausts that use steel wool wrap the steel wool around a perforated pipe inside the muffler chamber. Also unless you are using stainless steel wool it will rust and make a mess in no time.

BP