Exhaust system noise - help please.

[IanE481]

Hello,

I have recently purchased the entire "RoadsterSport MAX POWER MX5 COMPLETE EXHAUST COMBO...WITH UPGRADE TO CERAMIC COATED HEADER and HELMHOLTZ Midpipe" for my 2006 GT.

I love *most* of the sound. But when I really put "my spurs" to it as Brian says in one of his video's I get a slight metallic ringing sound at mid-high RPM. I'm really disappointed in this as I love the rest of the sound. It does not show up in Brian's on line videos. I love everything else about this kit... but I need to rectify this.

I have about 1,500 to 2,000 miles the system since install.

Any ideas? Really loving most of this sound.

Thanks!

Ian

[Brian]

Not much on exhaust system can ring, first idea I have in that regard is slight vibration of helmholtz chamber in the circle brace with round hole around the helmholtz chamber that supports it. That circle brace around helmholtz can is intentionally a little bigger diameter than the helmholtz can diameter so as to offer support and yet allow for heat expansion and a little movement, but perhaps on yours there is some resonance with that gap. Let's do an experiment, grab some high temp liquid RTV silicon exhaust gasket and smear a good amount in the joint between the can and brace. It will dry to rubber-like consistency that will still allow for heat expansion and movement but damp any vibration there. Drive again and report back.

If that is not it, then something else on the car is vibrating in response to the higher exhaust volume. These can be hard to track down, can be braces, heat shields, etc. This will often be the factory heat shields that are under the car in various places. The only trick to fixing those is usually to bend them a little without breaking them at the retaining rivets where they attach to the car, but some customers report good results with applying sound proofing mats to the heatshields that have heat reflective coatings (made by dynamat and other companies). Don't need to coat entire heatshield, just a little strip on big metal panel will often cure it.

[IanE481]

Excellent. Thanks for the suggestion Brian. I'll try to get at it sometime this week and I'll report back.

Quick question: I have this in my toolbox, will this work?

https://www.permatex.com/products/gaske ... ket-maker/

If there is something more suitable, please advise before I goop it up around the joint.

Thanks,

Ian

[Brian]

Excellent. Thanks for the suggestion Brian. I'll try to get at it sometime this week and I'll report back.

Quick question: I have this in my toolbox, will this work?

https://www.permatex.com/products/gaske ... ket-maker/

If there is something more suitable, please advise before I goop it up around the joint.

Thanks,

Ian

Yes, that's the perfect choice...for the older design. If you just bought it then with some food in me (long day that started 4am) I recall we revised and reversed the bracket design recently and pic below is new version that I understand is now shipping. Now the bracket end is just welded to side of helmholtz can (blue arrow) and the hole through bracket is now around the pipe (red arrow) and welded rather than free floating like the old design. I don't think there could be enough movement at that welded connection to possibly give you the ring you describe. Assuming those O2 bungs now have O2 sensors and not loose plugs....then I think you are back to hunting something else moving/vibrating in response to the exhaust notes. Heatshields, something loose.

If yours is older version, and bracket goes all around the helmholtz can at location of blue arrow, then try what you found in the toolbox at that gap.

[IanE481]

Okay. I was hopeful with your first advice as that sounded VERY possible. The sound could be a slight vibration that is a result of high rpm. I'll climb under there this weekend and nose around. Is there any chance that a vibration can be occurring between the mid pipe and the muffler? I used the crushable gasket. With your flange design it is not possible to over tighten, is it? Doesn't sound like I have a leak. I'll go spend some good amount of time with a light and report back. I'll try to "adjust" a few things as well.

I put anti seize in the O2 sensor relocations. I'll check the O2 plugs too.

If you have any other thoughts please fire away!

This is distracting me from my research of what kind of upgraded exhaust I need (want)!

[Brian]

Thinking about your description of the sound.....a ring. Got a tiny little 3 inch diameter heatshield around one of your O2 sensors right, first sensor?

[IanE481]

I found it!!!!

I put the car on stands (my wife now has approved a lift ) and FOUND THE PROBLEM!

The exhaust has decided to move slightly closer to the mid-pipe hanger since install. The exhaust is a bit high in the car. Under higher acceleration with more torque transferring through the exhaust (or engine shift) it was enough to vibrate the pipe against the metal hanger. I removed the hanger, took the car down and went for a drive. The noise is gone!!!!

Now I need to adjust the angle (and attitude) of the bracket and reinstall.

Sorry to bother you Brian. But I'm SO relieved. LOVE the sound now.... completely!!!!

I have two photos if I could figure out how to insert them quickly. But I must run now. Thanks again. I appreciate your fantastic customer service. Now about that suspension upgrade...... for another day.

[IanE481]

Houston... we still have a problem.

I fixed one issue. I still need to heat and bend the mid pipe hanger so it won't rub.

But today I drove it more aggressively to work and the crux of the problem is still there. Last night I didn't want to put my foot into it too much as respect for my neighbours so I thought I had it fixed.

But when I aggressively accelerate around 3500 rpm a tinny-raspy-ricey type sound develops. I've been looking at everything under the car tonight but get a sense it's coming from the Helmholtz pipe setup. I hate it. It sounds like a rice rocket under high load. Yes... it doesn't drone but this isn't cool.

More research on miataforum shows many are reporting this issue while others are not.

What options do I have to fix this? I'm not interested in paying all the shipping from Canada back to California. Shipping will eat up the a lot of the cost of me just getting a different exhaust manufacture. Help please.

https://forum.miata.net/vb/showthread.p ... ost9023292

[Brian]

People in forum talking about 10 different things with last person talking 'rasp', which is a million miles from 'ring', not 'this issue' you described as a 'ring' at all. Somebody wanting less rasp wants more fiberglass packing (or needs to stay with catted header since going catless is what releases massive additional rasp down the system). Rasp is not a small metal item vibration that would ever be described as a ring. Back to my previous post, got 3 inch dish shape heatshield on your first O2 sensor? Very small item that can 'ring' if loose, often needs to be bent to stop.

Found a picture, added blue arrow to the heatshield for the sensor. This is 'solid' on there from the factory but the act of installing the full exhaust system and moving this from stock header to new location can leave this item loose on the O2 sensor shaft. Result is a perfect little bell that really does 'ring' and ring and ring. That's the number 1 source of 'ring' noise. But there are other heatshields from the front engine bay all the way to under the trunk in the back and any of them can ring with the greater volume of a performance exhaust system. Over time the rivets get loose that hold the heat shields. Number 2 source of ring from a heatshield is the big one that hangs under the trunk. Other sources include either of the O2 sensors not tightly installed, or coming loose (common), and any unused O2 bung on the system (sometimes Tuners disable the second sensor and customers don't install it but also don't make the second O2 sensor bung plug tight and it will ring and ring until it eventually falls out and they report the exhaust system has busted open because it is so loud suddenly, but it's really just a fallen out O2 sensor or O2 bung). The exhaust system itself has no items that can possibly ring with the lone exception of what I described in my first response for prior generations of Helmholtz design where a dab of exhaust silicon sealant will prevent ring between circular bracket and helmholtz can.

[IanE481]

I will check it again.

It’s so hard to describe a sound.

This weekend I’ll try to get an audio recording and we can go from there.

Low RPM I love it. But something is not right at a higher rpm under load.