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Old 01-09-2006, 11:05 AM
DanDE's Avatar
Join Date: Mar 2005
Location: Delaware
Posts: 130
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Exhaust Modifications on a BMW X5 4.6is

Contributed by: DanDE

Hi guys,

Time to give a little something back to the board. I'll try to be methodical about this write up. Remember, this applies to an '03 X5 4.6is.

My goal was to have a throatier exhaust and retain my stock tips. No other modification was more important to me than this one. The vehicle has a 3 year lease. I didn't want to dump a ton of money into something that had to come back off without knowing if I would a) buy the vehicle after the lease, b) get another X5 - and would the after market exhaust even fit it c) what it sounded like. Another consideration was that it seems the 4.6 has a number of nuances that seem to affect only what I want to do to it. One of those will be evident further down in this post.

I'd read all about the Eisenhaus, but it was pricey and I was concerned about the loss of power and the hassle with getting stock tips on it. I'd read about the Remus. It seemed like a good value, and even though tips were an issue I was very close to buying it. Both of these worried me with not just the "tips" issue, but would I end up with some side effect I would have to tolerate.

I am very glad I did not do any of the above.

It involved some low cost experimenting and a lot of my time. But when all was said and done, in my opinion the result (both in knowledge and looks) is better. Had I known up front what I was able to "drill down to" at the end, it would have been helpful. I hope this will be useful to someone reading it all.

So, here was the sequence.

1) I left the stock resonator on and removed the stock exhaust. I had a muffler shop bend pipes, bolt them to the stock resonator and put a small set of glass packs with dumb looking tips on. It was about $300 total and gave me an idea of sound. If I liked it, my only real additional expense would have been the right tips. Here is a picture with the "cheesy" set up:

Sounded very good, but a rattled developed INSIDE the exhaust during cold running. The rattle was loud, annoying, but went away after a minute or two. Those who know me and my complaints about the unrelated shifting noise systemic to 4.6's know I don't tolerate this sort of thing. There was also some loss of power.

2) I put the stock exhaust back on, had the stock resonator removed, and put straight pipes on in the stock resonator's place. Man, did it sound good. REALLY good. But, that cold rattle was still there, and there was a loss of power. I tolerated both of these downsides for a while, as I had my stock look and it sounded so mean. But finally, decided to keep trying. Here is a picture with the straight pipes in place of the resonator and the stock exhaust intact:

3) Had the straight pipes removed, and 2 small resonators fit in their place (in place of the stock resonator). BINGO. Sounds much better than stock, have my stock look, the cold rattle is cancelled out (you can just barely hear traces of it on a cold start), AND I have my power back. I can't tell you much about the resonators the shop used, other than they are nothing more than small straight through glass packs - perfect. They are 12" long with pipes and flanges welded on each end. I don't know the make, but after calling the shop was told they were probably Walker or Arvin (spelling?)with either a 2" or 2 1/4" diameter. Here is a picture of the modified resonators with stock exhaust intact:

Thing is, I wish I had known about the "rattle" to start with. I would have saved a lot of time and a few hundred bucks. Still happy about it all though, as overall cost was a lot cheaper than the Eisenhaus and I have my stock look. I'm just not sure if at the end of the lease when I put the stock resonator back on if they are going to give me a hard time, but I have it flanged and ready to bolt right back on. Crevier said they accept turn ins with modified exhausts put back to good working order - and that is the language in the lease. So I'm comfortable with it.

Now, when working this through, rattled with resonator on but not stock exhaust. Rattled with resonator off but with stock exhaust. Both cases some loss of power. Stock exhaust with modified resonators worked. My conclusion is that the 4.6 has some type of pre-resonator detonation or something that you simply have to have cancelled out. I spoke with //MB46 on the roadfly board, who has an Eisenhaus, and he has this cold rattle with that exhaust. Surprised, as I've never seen it mentioned on the board by Curtis or ArtX (my heroes!) who I think modified their exhausts. My guess is if they have the Eisenhaus, they have the rattle too, but put up with it. (Like a lot of 4.6 owners who put up with the shifting noise, except THAT standard feature comes from the factory).

Bottom line, since none of these after market exhausts seem to improve performance, why not do what I did in part 3 above. It will only be a $200-300 mod., no rattles, stock tips, great sound. You just have to spend a couple of hours at a muffler shop you are comfortable with. My guess is that cold rattle is unique to the 4.6 and won't be an issue on the 3.0 or 4.4. I would do it to any of these models if throatier sound and stock appearance is what you are looking for.

In the above photo of the installed aftermarket resonators, note that they have flanges welded on both ends so it is simple to unbolt. I had flanges welded on the pipes from the cats to the resonators as well as the cut side of my stock resonator. This way I can unbolt this mod and bolt back on the factory resonator anytime I want. If you choose to try this mod, you could just have everything welded in place. Here is a photo of the factory resonator ready to go back on:

Good luck and enjoy!

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