Exhaust system noise - help please.

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Re: Exhaust system noise - help please.

Postby Brian » Wed Jul 18, 2018 5:12 pm

Updated my last reply with picture of the most common 'ring' source and additional source of 'ring' notes.

I should also note entire system will be rather metallic sounding when new because you got a ton of bare metal in there. Over the first 1000 miles carbon slowly coats all those surfaces and damps that out of it's character, it mellows a ton. So, if something is really vibrating it will actually stand out more with some miles and be easier to locate. Otherwise, put the car on a lift, have somebody rev the gas while it is on the lift so you are making exhaust noise in same RPM range where you hear the ring, that makes it MUCH easier to chase down. We do that all the time here and we have found all sorts of things that can ring.

On my Racing ND this was the source of a ring, a damper that is hanging from the rear of transmission with loose rivets. NEVER seen this item as a source, would not likely have found it without running the car on the lift with several of us under the car in the hunt for the ring we could hear when driving. Look close and you can actually see the rivet nearest the camera is loose, not flush. Talked with friends at Long Road Racing (they build the Cup Cars) and found out they remove these to save weight, it is a solid couple of pounds and designed to reduce NVH. Thus, the irony here is item designed to reduce NVH was adding it instead. Having never seen this as a source of ring, I ended up giving this item back to Dave Coleman (Mazda Engineer) so they could send it back to Japan to look at how to prevent these rivets from failing in the future.
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damper.jpg
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Re: Exhaust system noise - help please.

Postby IanE481 » Thu Jul 19, 2018 6:41 pm

Thanks Brian.

I have checked the 3" shield on the first 02 sensor and have been checking, damping, bending, removing, reinstalling all the shields I can find. I've even stuck a rag under the fuel filler door! Other than raising my frustration to new heights and spending hours under my car I have made no progress. I'm so sick of floor jack and jack stands I can hardly tell you.

I even borrowed a friends Racing Beat muffler and installed it. The sound was WAY louder at 3500 RPM and up under load. It was REALLY horrible and ricey sounding. I reinstalled my SuperQ quickly.

I'm getting a lift installed next Wednesday so I'll ask a friend to help me try to do more isolation.

I do think that something is off with their mid pipe in another way. I've adjusted, clocked, etc the slip joint a dozen different ways but there is no way that the pipe will clear the mid-pipe hanger (most clearance I can get is about 1/2"). The only way I can make the hanger not contact the mid-pipe is to heat & bend the stock bracket (something I'm not going to do until I know if I need to find another mid-pipe solution). I'm a decent "shade tree" mechanic. I've installed after-market exhaust on 4 Miata's (including a full Roadster Sport exhaust) and 2 other full systems on a Porsche (Borla) and Ferrari (Tubi) and I've never had such an obvious misalignment for a hanger.

I have a "out of the box" solution I'd like to try but can I contact you in person (or at least not play out on the forum here)? Can you pm me a contact information or tell me the best way to touch base for a few minutes?
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Re: Exhaust system noise - help please.

Postby Brian » Fri Jul 20, 2018 9:28 am

If pointing lower half of rubber midpipe hanger forward that's usually telling us the system adjusted too short at slip joint. If midpipe pointing lower half of rubber hanger to the back of car that's system stretched too long. After that it's clocking position and there is quite a bit of available play in clocking position, find the position that doesn't have the hanger knocking and only then do you lock the bolts at the connection to header and work your way back with slip joint and then muffler.

All this assumes healthy motor mounts and diff mounts. When the motor mounts are worn the entire system will slump off to one side, making alignment of exhaust system difficult or impossible without updating the fading away mount or cutting off and/or bending hangers. Same results with worn diff mounts.

After that I am out of ideas for now, hard to diagnose this stuff long distance but call the phone number on our site and talk with our crew, Ryan in particular built his V6 time attack Miata and knows his way around these parts. In fact, entire crew answering phones all wrench and they are in close proximity to head mechanic Rocky (who has installed more of these than anyone). I am not in the shop all this month, at our new location with the Contractors all month trying to get it ready for moving next month (poor cell service here, and no regular phones until at least next week). Yesterday was 4am start framing walls and 6am to Lowes for drywall, similar today with just short breaks when I can check stuff on slow connection while I chew some food (this is breakfast now). So, I am in a connection black (or at least grey) hole here at least until the AT&T crew gets here late today to help lay fresh Cat5e lines through new walls we have framed so high speed is available throughout our new space. Then hopefully phones get added next week.
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Re: Exhaust system noise - help please.

Postby IanE481 » Fri Jul 20, 2018 2:52 pm

Thanks Brian. I'll try again with the slip joint when my lift is installed next week.

But more importantly I had a great chat with Ryan and we have a good game plan on the annoying sound issue. Great customer service so that helps the frustration level.

Don't work too hard on your build!!!
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Re: Exhaust system noise - help please.

Postby IanE481 » Fri Jul 27, 2018 4:45 pm

Hello,

I'm still waiting for the glass pack baffles to see what change they make to the system. But since I got my lift installed to today thought I'd make a short video as it's easier to identify a sound on a video than someone trying to describe it with words.

Sorry for the orientation of my phone but it's my first video. https://www.youtube.com/watch?v=CMuLooAJmq0

Interested in your thoughts. I'll get the baffles early next week. Once I install them I'll see what they do then I'll call the office.

Regards,

Ian
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Re: Exhaust system noise - help please.

Postby Brian » Fri Jul 27, 2018 5:44 pm

IanE481 wrote: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


Grab that tube of gasket maker. As the video goes past the helmholtz bracket I can see weld does not go all the way around, there is some gap between bracket metal and pipe. That's intentional but let's fill that gap. I am skeptical it could rattle in that gap but let's see what happens if we eliminate that gap with something that will act as a damper.
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Re: Exhaust system noise - help please.

Postby IanE481 » Fri Jul 27, 2018 6:17 pm

Okay Brian. Will do first thing in the morning. I inspected the welds and they are all intact with zero cracking. The welds are nicely done and high quality. Seems they purposefully leave a gap between the welds. I carefully inspected that gab and there is no rubbing.

I'll put a good amount on it to see if that helps dampen. Kinda takes me back to my "Vibes" classes in Engineering school. I'll try anything right now. As I walked underneath it with my wife blipping the throttle it didn't seem to be any vibration as much as acoustical flow noise... if that makes any sense. The exhaust seems to hold rock solid.

I'll try it and let it cure then get back to you. Thanks for helping!
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Re: Exhaust system noise - help please.

Postby IanE481 » Fri Jul 27, 2018 6:19 pm

Actually going to go do it now so the gasket maker can cure overnight. I'll delay my movie night with my wife and get this done first. It's driving me crazy and becoming an obsession to fix. :?
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Re: Exhaust system noise - help please.

Postby IanE481 » Fri Jul 27, 2018 7:03 pm

Okay. Done. All gooped up. Ensured the gap has been filled and had a good liberal amount around the holder. Will test tomorrow.


What the heck did I do before I had a lift! :)
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Re: Exhaust system noise - help please.

Postby jboemler » Fri Jul 27, 2018 10:19 pm

IanE481 wrote:As I walked underneath it with my wife blipping the throttle it didn't seem to be any vibration as much as acoustical flow noise...


That was my impression from the video as well.
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