[BrianMN]

Well, at least I tried....

There is a rubber dampener on the rear end of the OEM exhaust system, and I attempted to fit it to my AMS single 3" exhaust. I was hoping to reduce the already mild drone in the 1800-2000 rpm range.

Cutting off and re-locating it was simple...simple cut and weld. I tried to make it fit as closely and similarly as stock, and think that it couldn't have been closer to stock placement.


So, the results: Well, I was hoping to reduce a bit of drone, but there was no noticeable difference. However, there was a great reduction in cold-engine rasp. As with most aftermarket exhausts, the cold-engine exhaust tone and rasp can be quite ricey....but this really smoothed it out and cleaned it up!

If you have your stock system hangin around, get choppin!

[Sniz]

thats a good idea, hell I could weld one of those to my 3" exhaust and it might help a bit.

[bulldog_yyc]

^ thats a good point, more of a trial and error approach here but at least it seems to help somewhat

[Jeff@TopGearSolutions]

So that thing just sits there to supposedly reduce noise. Interesting.

[BrianMN]

Originally Posted by maxnix

The problem is that is placed to dampen a primary resonance in the stock system. Who knows at what frequency the after market system is?

very good point.

These rubber things can be found on a lot of cars...some Audis have HUGE rubber things that must weigh 10 or 15lbs!

The drone is still something we need to engineer a fix for, but it's good to know that this rubber dampener helps with the rasp!

[mycoupe]

I have a friend who got her masters in mechanical engineering with a focus in harmonics and vibrations...I could give her a shout and she might have some ideas on how to figure out the necessary location mathematically.

[joyride]

Originally Posted by mycoupe

I have a friend who got her masters in mechanical engineering with a focus in harmonics and vibrations...I could give her a shout and she might have some ideas on how to figure out the necessary location mathematically.

That is who they have have work on that. You can have her go over idea, and maybe suggest a way to find the correct spot to mount the dampener. But each system will be be different, I think.

I've planned on testing this out as well, but with some sort of clamp at first to try different spots on the exhaust, then tacking it on if/when a good dampening spot if found.

[Transport3r]

Try a spot which is furthest away from any hangers.
The maximum amplitude of the vibration is most likely to happen between these fixed points (also called nodes).
The problem here isn't placement, but more likely the weight and stiffness of the actual damper. These need to be tailored to the specific natural frequencies of the system. Since the weight and stiffness of your new exhaust is different than the stock one, the stock damper is out of tune with the rest of the system.
Ideally you would carry out a modal analysis of your exhaust system, but you need either very expensive equipment or software.

[Tzu]

The problem IS placement. Regardless of the stiffness of the exhaust dampers, the natural frequency between the two nodes remains the same at the different spring rate of the new exhaust. The longer an unsupported section is, the lower the natural frequency is. Mass loading the longest section, or conversely placing a support between it, would make the natural frequency occur at much higher rate of oscillations.

However, hangers themselves act as springs. So an exhaust system with 2 hangers, with exhaust piping being suspended from each hanger would in turn have 3 natural frequencies, as a function of the exhaust mass and spring rates per length. Factor in the hanger spring rate multiplied by the number of hangers, and now we have some complicated math. Even if you were to map it all out, it would still be theory only, without accounting for all the bends in the exhaust.

Point being, it's probably better to trial and error this kind of thing. Something that works on your car, may not work as well on mine.

[Chrisred]

Originally Posted by BrianMN

Well, at least I tried....

There is a rubber dampener on the rear end of the OEM exhaust system, and I attempted to fit it to my AMS single 3" exhaust. I was hoping to reduce the already mild drone in the 1800-2000 rpm range.

Cutting off and re-locating it was simple...simple cut and weld. I tried to make it fit as closely and similarly as stock, and think that it couldn't have been closer to stock placement.


So, the results: Well, I was hoping to reduce a bit of drone, but there was no noticeable difference. However, there was a great reduction in cold-engine rasp. As with most aftermarket exhausts, the cold-engine exhaust tone and rasp can be quite ricey....but this really smoothed it out and cleaned it up!

If you have your stock system hangin around, get choppin!

How u like that exhaust. I find it's not loud enough on higher rpm. And I have catless dp's. I also noticed a vibration coming from inside car. It sounds like the center console.

[BrianMN]

Originally Posted by Chrisred

How u like that exhaust. I find it's not loud enough on higher rpm. And I have catless dp's. I also noticed a vibration coming from inside car. It sounds like the center console.

I guess I'd have to disagree on the loudness...I think it's just about right.

Regarding the vibration: sounds like you have an install issue...

[Chrisred]

Originally Posted by BrianMN

I guess I'd have to disagree on the loudness...I think it's just about right.

Regarding the vibration: sounds like you have an install issue...

I don't think it's an install issue cause sound is definitely from inside. It's like a plastic vibrating sound like the center console. There's been talks that it's the console here on forums. U have E90 or E92?? I have E92. And do u have downpipes??