EXHAUST FROM HELL PAGE.
This one was actually started before the ram air, but it has been such a pain that it is still on-going. I wanted to upgrade the flow of the exhaust and also have a couple of cool tips like my wifes E36. I searched the Roadfly-E39 archives for any info I could find. I found that a lot of people remove the resonator (V shaped ugly box in the center of the exhaust behind the catalytic converters) install a 3" pipe from the catalytic converter to a new muffler and use Magnaflow mufflers. I was dumb enough to follow it, and now I have to deal with the consequences of a car that sounds like a Honda with a fart muffler. The drone is just too much. The problem comes when you open up the exhaust with the 3" pipe and install a free flowing muffler that does not have a resonant chamber built in. The 540 has a European exhaust pipe that I believe is 66mm. Measured with a caliper it looks like 2.6". In the US you can only purchase either 2.5" or 3" exhaust pipe. The 540 can only accomodate a 14-15" muffler in the back so I selected a 14" body stainless steel Magnaflow muffler #14221 with a single 3" input and dual 2.25" outputs and had Stainless Steel tips welded on the outputs. This combination of very low restriction muffler and a very large pipe produced a ricy drone between 1200-1700 rpm.
Do not do this unless you like drone. There is a reson why BMW put that resonator in there with a 2.6" pipe. A 3" pipe with no resonator is just too much.
I believe that a 2.5" pipe with a nice free flowing muffler is all that this car needs if you want to take out the resonator. I would only use a 3" pipe if you are going to supercharge it. This is NOT a big block motor and a large reduction of backpressure really hurts performance, not helps it.
On the suggestion of RevHigh from Roadfly I tried CarChemistry inserts to re-apply some backpressure in the system and remove the drone. I used a 3 disk insert and it did help a little bit. There is less drone, but it has not been completely eliminated. The CC inserts work by mixing cold and hot exhaust gases to reduce sound, so you have to install them as close as possible to the collector past the cats. Maybe if I went with a 2.5" 3 disk insert and installed right inside the 2.6" pipe where the 3" pipe connects to the 2.6" it would have worked better. Just a sugesstion in case someone is trying to do the same. After driving for a few days I noticed the MPG go up from 24.5 to 24.7. Not a lot, but it shows that these motors work better with the right amount of backpressure. After some more research, I found out that it is OK to install more than 1 CarChemistry insert into the exhaust. That may be the next option. The other option would be to add a pipe perpendicular (at a 90 degre) to the main exhaust pipe to tune out the resonant frequencies (AKA BMW resonator). The following link has everything you would like to know about exhaust noise.
Performance wise, without the CC insert the car felt like it lost power. Once the insert was installed and the CPU recalibrated for the new backpressure, the power came back. I just can not tell if there was any improvement over stock. I probably will not notice any difference untill I install the AutoT software. The exhaust by itself does not do a lot.
One thing that I forgot to mention is that, if all you are looking for is tips and some sound, my suggestion would be to just install a universal muffler by a custom exhaust shop. Magnaflow has a distributor list on their website and a lot of them will install a universal muffler for a fixed price. When it was my time to pay for the initial installation the guy points to a Stainless Steel muffler with 2 DTM tips on the wall and sais "we sell this one for $130 installed". Had I known then what I know now, that is what I would have done.
I am now using a Borla Stainless Steel muffler. I removed the Magnaflow and the CC insert and installed the Borla. It has a 2.5" input and 2 intercooled tip outputs. It is also a streight through design like the Magnaflow, but of better quality. It is 14x8x5 in size.
It sounds better, some of the drone is still there, but less of it. The sound is a little deeper. Has a nice rumble to it as I go through the gears. I did loose some of the low end torque I had due to the extra backpressure the CC inserts provided. It no longer jumps when I let go of the clutch, but still feels strong enough. Stronger than stock. I am thinking of putting a round resonator. If I do, I will probably go with a 2.5" in/out and have the ends expanded to 3" to mate with the other piping. The 2.5" size sould add some backpressure, so that I can get the torque back. I want to keep the 3" piping in bends, since that is where exhaust flow is most critical anyway.
Here is the good part. This muffler is from a C4 Vette set of mufflers. It is Stainless Steel with stainless steel packing, so it should never wear out. It has a 2.5" input opening, box size is 8x14x5, and already has 2 intercooled tips on the output that are at the widest 3.5" round each. Can be easily mounted under the E39 rear muffler opening once the old cans are cut out. It weights about 16lbs. It would need to be a custom instalation though. Many manufacturers make C4 mufflers. Borla and Corsa make excellent mufflers for the C4 Vette, depending on what you want. They have baffled and streight through designs, so you have more choices to choose from.
using the Borla page or the Corsa page, you can choose different years between 1984 and 1990 to see if other types of tips interest you. I ended up selling the other muffler from the set to offset the cost. Most of them , it does not matter if they are mounted on the right or left side. Places like http://www.summitracing.com/ sell Borla at a discount, but you can also get them at other high performance specialty stores too.
Well, I finally found some time to install a Magnaflow round muffler/resonator between the cats and the Borla muffler. I installed one of the Stainless Steel round, 14" long, 4" wide can, with 2.5" in/out opening. I had a local shop expand the openings to 2.8" OD to fit in my 2.8" ID/3"OD SS pipe. It is a waiste of time and money as far as sound is concerned. It is not a resonator, it is a muffler only. It muffled the exhaust throughtout the entire rpm range, not just removed the drone. It reduced the nice rumble I had above 2000 rpm, and it did reduce the drone level a little bit, but did not remove it. What bothers me the most is that the drone is still there, but the 2000 rpm and above rumble is gone. To me this was not worth it.
Magnaflow product page for this muffler.