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Driveline, Engine & DME Tuning
Talk about driveline improvements, NA tuning and DME tuning your E46 BMW here. This includes diffs, intakes, exhausts, chips, software and OBD tuning.

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Old 04-13-2015, 09:32 AM   #1
jared_wiesner
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Jared's DynoMax VT Rattle Fix

I feel compelled to share this as I have had a rattle in my dynomax VT muffler since shortly after install a few years ago and there is not a single documented fix available on the internet that I have been able to find. Many are using this muffler for performance exhaust setups as it provides both quiet drone free cruising and straight through flow at wide open throttle. It really is the best of both worlds. The problem is that with higher flow and especially in cammed applications the muffler will develop a very annoying rattle at idle and any transitions to off throttle.

The problem is caused by the way the muffler works to be quiet at cruise and open at WOT. There is a spring controlled flapper valve in the exhaust tube going through the muffler and especially on cars with less than even exhaust pulses the valve will flap open and shut quickly. This causes a rattling noise that sounds not unlike a very annoyingly loud heat shield rattle and makes your otherwise great sounding exhaust sound like it belongs to a clunker.

I searched and searched for someone that had come up with a solution but most just say that DynoMax has released an updated design with a steel wool pad for the flap that solves the rattle. Well, the problem is, I have the updated design and it still rattles horribly and many others are in the same boat.

I realize this is a lot of lead up. But, to understand the problem, necessary.
The solution was quite simple. I drilled a hole through the bottom of the dynomax vt muffler in approximately the same location as the bottom of the flapper valve where it contacts the pipe. I drilled through both the bottom of the muffler and kept right on drilling into the pipe inside. Then, I screwed a long decking screw up through the muffler while the car was idling (and making an awful rattling racket) I continued to turn the screw up until it contacted the valve and the rattle stopped. I gave it a few revs to make sure the rattle was stopped entirely and turned the screw a hair more until it was. Then I spot welded the screw where it went into the muffler. Grind off the excess protruding screw. Finish welding the screw fully on the outside of the muffler and voilą. No more rattling Dynomax VT. It's now everything that dynomax promises and it sounds great too!

For those with rattling dynomax VT's pulling their hair out. Enjoy!

**Edit** added reference photos.
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Old 04-13-2015, 10:17 AM   #2
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Nice!
Maybe posting a pic of the screw location would help.
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Old 04-13-2015, 10:21 AM   #3
jared_wiesner
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Added reference photos to the original post. (my muffler has had the corner of it taken off to provide more ground clearance so its not the best reference photo.)
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Old 04-13-2015, 11:23 AM   #4
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Old 04-13-2015, 02:55 PM   #5
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J, I understand how your DM muffler works, I would think what you've done would interfere with the movement of that flap. Does your welded in screw "slightly" hold open the valve a little more which in turn provides a new tensioned resting place ? Thus no more rattle.



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Old 04-13-2015, 03:00 PM   #6
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J, I understand how your DM muffler works, I would think what you've done would interfere with the movement of that flap. Does your welded in screw "slightly" hold open the valve a little more which in turn provides a new tensioned resting place ? Thus no more rattle.



Rob43
Exactly.

It's still free to open fully and it just stops short of fully closing and hitting the wall of the pipe. It is not at all noticeably louder without being able to close fully. (If anything its quieter now that it doesn't rattle)

Really it's just a re-think of the fix that Dynomax themselves tried to implement with the steel wool pad. The problem is that pad for whatever reason wears away/begins to rattle after a short time as well. (Especially in cars with cams)
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Old 04-13-2015, 03:30 PM   #7
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Damn cams, can't live with them,......can't live without them.

Anyway, it's good you got it fixed.



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Nitrous is a little trickier than boost, but it's not the spray that kills motors, it's STUPIDITY!!
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Old 04-13-2015, 03:44 PM   #8
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Damn cams, can't live with them,......can't live without them.

Anyway, it's good you got it fixed.



Rob43

Haha yes cams, of any kind, really are essential

The interesting thing is that even dynomax have given up. They have a guarantee that you will be satisfied or your money back. They have since added a disclaimer (unless you have performance camshafts) Back when I bought the muffler they had no such disclaimer related to camshafts. They just said to use the mufflers with the more powerful spring designed for higher displacement engines when performance cams were installed. Didn't work for me.

Though, the internet is full of people complaining of the rattle even in cars with stock cams. So, it's just a poorly thought out design in terms of the rattle. I can think of other seamless ways to prevent it other than what I did. However, all of them would take much more work and would require fancier materials to implement.
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Old 04-21-2015, 07:13 PM   #9
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best muffler that works: Expensive though but I love mine.



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Old 04-22-2015, 06:11 AM   #10
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ive read somewhere (dont recall where) that a good resonator before the VT muffler helps, by attentuating the amplitude of the pulsing pressumably
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Old 04-22-2015, 04:53 PM   #11
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Jared's DynoMax VT Rattle Fix

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ive read somewhere (dont recall where) that a good resonator before the VT muffler helps, by attentuating the amplitude of the pulsing pressumably

Had one, did nothing, even rattled with a cat and a resonator before it. Now there is no rattle and there is nothing before it.


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best muffler that works: Expensive though but I love mine.



Looked at these at one point, couldn't justify the price. Honestly my exhaust sounds perfect now for the cost of a decking screw.
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Old 05-13-2015, 10:22 AM   #12
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Just an update. Was driving the other night with a buddy behind me. Did a quick blip and downshift and shot a good size race car flame out of the exhaust. (Tune still isn't fully dialed in, apparently especially under low loads seen during a blip)

Later that night I noticed a horrible rattle from the dynomax vt that progressively got worse and sounds like more than the flap. Likely something has broken free from its weld inside.

I'm done with the dynomax. I would like the varex but it's very expensive (varexpensive, sorry) and I find it would still be annoying to play with a blend between power and sound all the time. It's also just more to go wrong. I'm inclined to just get an electric cutout in the future for track use if I decide it's necessary.

In the mean time, I've ordered a factory bmw performance dual in/out muffler from ecs and will be splitting my 3 inch near the axle to go back to the dual outlet muffler. Should sound good, quieter, and cost relatively little power.
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Old 06-06-2015, 09:28 PM   #13
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OP - thanks for posting. I was in the market for a Dynomax VT for my track car. I drive to/from the track and didn't want to deal with drone so I was really leaning towards this muffler. However I read numerous threads about how even the updated muffler still rattles. Wasn't sure if these are one off's or just a flaw in the design. You've convinced me to stay away. Let me know if you end up finding another muffler that suits your needs. I think Flowmaster Hushpower (round) or Delta 50 (oval) are your best bets.
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Old 09-10-2016, 06:15 AM   #14
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Although i am not a BMW owner i found this thread to be very helpful with fixing the rattling coming from my dynomax vt mufflers, so i felt compelled to share my findings with the community in hopes it can help someone else.

BLUF: If you have strait pipes that dont equalize the pressure between the 2 pipes, your dynomax vt muffler will rattle.


I drive a 2012 Hyundai Genesis 5.0 r-spec and wanted a little but more audio feedback from my driving experience. The stock mufflers are as quiet as church mice and very restrictive. I read about these dynomax vt mufflers and thought this is exactly what i was looking for, regardless of some of the poor reviews.

I initially switched out the mufflers and it sounded good, but not really loud enough for my liking. I did feel a very slight low end torque and power increase from this (whether it was actual or just psychological i don't know)

From there i took out the resonator. The sound was much louder but then the flapping started. While idling, accelerating, and downshifting, there was a horrible and embarrassing rattling coming from the back of my baby.

I did my research and found that an unbalanced exhaust system (if its a dual exaust) has the potential to cause the flapping due to unbalanced pressure between the two sides or some technical nonsense like that. I went back to look at my resonator and sure enough there was a H-pipe hidden in there (thus the absence of rattling initially).

I put in an X-pipe in place if the two separate, and voila, no flapping, rattling, or clanking. It sounds much cleaner as well, a little softer, but if you are looking at this thread at all, your probably not looking for obnoxious loud sound anyways.

And as far as the "drone free performance", i couldn't be happier with my product (only had them for a month, this could change). Accelerating sounds great then quiets down when cruising, even at highway speeds. Starting it up is my favorite part though; nice, loud, and aggressive sounding start up, then it quiets down to a purring hum sort of sound.

If anyone has even reached it down to this point and are interested in a video, just let me know. I hope this helps someone else who has had this problem.
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