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chadillac2000 chadillac2000 is offline
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Posts: 599
Join Date: Jul 2011
Car: 2008 535i
Default 09-12-2016, 08:24 PM

The combination of the BMS ******* *********, OEM N54 midpipes, and the Maddad Whisper axleback had produced nearly the exact sound I was looking for on all levels for my 1er. Subtle, aggressive, burbly and looked great out the rear diffuser. In an attempt to further fine tune the exhaust note and fitment, I had a few things I wanted to address. The first of which was to delete/replace the spring bolts (one of which was stripped during the initial axle back install despite using vice grips). The second was to replace the infamous bolt securing the midpipe bracket in place that was also stripped. The third was to adjust how high the Maddad Whisper tips sat; they were just a little too low for my liking. The last and most involved task at hand was to remove the midpipe, cut out the secondary cats, and weld in a pair of Vibrant 1790 bottle-style resonators in their place.

I chose to go this route over aftermarket midpipes or the N55 midpipe for the following reasons:
  • Most importantly, cost. Aftermarket midpipes are too expensive in my eyes and this setup was only $100 shipped for the pair of resonators.
  • My access to a welder/saw allows me to swap back in the factory secondary cats down the road if need be.
  • Looking to avoid drone/rasp at all costs, the N55 midpipe (essentially a straight pipe version of the N54 midpipe) is notorious for adding rasp.
  • This setup implements 3 total resonators (2x Vibrant 1790 + the large OEM one), which gives me my best chance with an aftermarket axleback and ******* ********* to keep rasp/drone/obnoxious volume at bay.
Removing the OEM midpipe was fairly straight forward. Despite only having 5,000 miles or so on the "bomb-proof" ******** to midpipe gaskets and hardware, they were trash after removal. 2 of the 4 bolts connecting the midpipe to the ********* sheared off. The close proximity to the turbos and extreme heat these bolts, nuts, and gaskets are exposed to just wreak havoc on their ability to be reused with any regularity.

Once I got past this small hiccup, I was able to fully remove the OEM midpipe so I could hack it up. The orientation of the secondary cats make welding in a straight piece of piping a little tricky. Fortunately the bottle-style design provides some additional room to resolve fitment issues.

While I have access to a nice MIG welder and gas, I hardly ever take advantage. Welding stainless steel to non-SS ended up being a little difficult considering my lack of experience, especially when I had some small gaps to fill because of the angles of the cuts associated with removing the secondary cats.

But I took my time, ensured everything sealed properly with no leaks or weak spots, and eventually the job was complete. I placed the secondary cats away for safe keeping in case I need to put them back in for some reason. OR I could probably find a scrap metal yard and break even on the purchase of the resonators. Again, not the prettiest welds but they will get the job done and sit well hidden under the car. Plenty of room when test fitted up in the exhaust tunnel. They actually sit even higher/tighter than the OEM secondary cats because they're smaller.

After I fitted the newly revised midpipe with resonators into place, I took this opportunity to do a few other things before tightening all the exhaust bolts, firing it up, and listening to the new snarl.

Working down my checklist of things to-do from the rear of the car to the front, I opened up the trunk area to install a set of recently acquired OEM LCI Blackline tailights.

This was a mod that I had been debating for the past few weeks. I didn't have any objection to the factory tailights, but after securing the Blacklines into place, these give the rear end a very updated look and the smoked shading looks great with the overall dark theme of the car.

To get the exhaust tips exactly where I wanted them, I used some simple worm clamps wrapped around the exhaust hangars (hidden out of view) to pull the tips up to the perfect placement. Now there is a uniform amount of space between the left, right, and top portions of the opening in the diffuser. Using slightly smaller bolts than the original holes, I then replaced the midpipe to axleback OEM shoulder bolts that had partially stripped during the initial axleback installation. Now the exhaust sits correctly, is tightened evenly on both sides, ensures a leak-free seal, and has a nut on the backside in place of the welded in version.

Moving forward, the next task was to address the bolt securing the midpipe bracket in place. This bolt is known for stripping easily and I was a victim of this while trying to tighten it into place during the re-installation. The tack welded square nut on the top side of the bracket had broken loose completely, so I was able to replace with a standard bolt/nut, which allowed for a much more secure fit than before.

As I mentioned previously, the heat of the ********* coming off the turbos had deemed the gaskets/hardware unusable after I removed them to disconnect the midpipe. This led to a trip to a local part store to try the 9547 Felpro gaskets that only cost a few bucks each, are in stock at most stores, and have been proven to seal up just fine. I also picked up some new 10.9 hardware. Total cost was less than $10 for everything pictured below with no wait time.

Fit perfectly and absolutely no leaks.

While I was under the car with access to the tie rod ends, I also took this opportunity to remedy a problem I'd been having since my last alignment. Since getting the car back, it tracked perfectly straight, but the steering wheel was off center; sitting about 2 inches to the left. This bothered me to no end, especially considering how much time I spend in this car. Using this DIY I found, I put ramps under the front tires and loaded it up, loosened the tie rod bolts slightly, adjusted the tie rods by the same amount and voila, the steering wheel was sitting perfectly straight. Worked like a charm.

(Pictures borrowed from the thread linked above)

The last task at hand was to see how much oil had been accumulated by the BMS and Mishimoto oil catch cans after 500 miles of mostly highway use to see what I would be dealing with as far as catch can dumping intervals. The BMS can was bone dry, but then again, I've only went WOT once or twice since it was added so that was somewhat expected. The Mishimoto can attached to the RB External PCV however, had caught plenty. I'll double check this one again in a few thousands miles, but this confirms that I should be fine waiting until my 5,000 regular scheduled oil change intervals to worry about emptying the catch cans.

Words cant explain how great I feel about keeping this gunk out of my intake tract.

While the car was still up on stands so I could check for leaks, it was time to fire it up and see what all the hard work I'd just done had resulted in. From underneath the car, I ensured that I was leak-free at both ******** to midpipe connections, the welded seams at the newly added resonators, as well as the midpipe to axle-back connection. After verifying no air was escaping from any of the exhaust *****, now it was time to soak in the new sound.

After a few drives, my initial impressions are:
  • Overall volume, if it could be quantified, is probably another 10% louder than setup I began this post with, and probably 25-30% louder than a full stock exhaust at this point.
  • Burbles on decel are increased and can only be described as intoxicating at this point.
  • Happy to report that still no drone or rasp at any RPM in any gear with the windows up or down.
  • WOT pulls through multiple gears are absolutely brutal -- so many sexy sounds.
  • Exhaust fumes have increased now that all four cats have been eliminated, but I've never been one to be bothered by ******* fumes.
  • The ******* *********, N54 midpipes with Vibrant 1790 resonators in place of the secondary cats, and the Maddad Whisper axleback produce EXACTLY what I was looking for.
A proper shoot to get some pictures/videos of the car is next on the agenda.

Visit Chadillac2000's 2008 135i Road Warrior Daily Driver Single Turbo Build Thread HERE

ACF PTE 6062 BB Top Mount ST Kit, Fuel-It! Stage 3 LPFP, Phoenix Racing Port Injection Manifold + RACE FMIC, JB4 + BMS ST E85 PI BEF

Last edited by chadillac2000; 10-08-2016 at 08:27 PM..
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