Here’s an overview of the problem: The design of the MazdaSpeed exhaust is such that it resonates within a range of frequencies, primarily between 3,000 and 4,000 RPM. The portion of the exhaust that responds this way appears to be from the end of the muffler that attaches to the tip, forward to the 1st cat and header. We’re effectively dealing with a tuning fork.

Because our part of the universe is causally based, cause and effect layer on top of each other just like ham on cheese. (I'm making myself hungry.) The resonating heat shield is an effect. The drone is an effect. My aggravation with the noise is also an effect. One way to solve the problem is to address the root cause – the resonating exhaust.

A way to look at the root cause goes back to the tuning fork analogy. When a tuning fork is vibrating, how do you stop it? If you alter the length of the tuning fork, you change the frequency it vibrates at. (This is the pipe insert approach.) If you grab the tuning fork, the vibration stops. (This is the weight attachment approach.) If you don’t tap the tuning fork in the first, it won’t vibrate. (This is the plug approach – it slows the velocity of the exhaust gas such that it doesn’t cause the resonance.) You can rubber coat the tuning fork - it still vibrates, but it doesn’t apparently make as much noise. (This is the Dynamat approach.) Lastly, you can do away with the tuning fork with a 14mm socket wrench. (This is the “MazdaSpeed’s sitting in my shed” approach.)

I don't think re-working the pipe transitions would have much effect - this would alter exhaust velocity somewhat, but I'm afraid the resonance would still be there.

Me? I’m just an ordinary guy who really likes driving a Protege5.

 

i don't think i could be better stated! judging from the responses and experiments given... there simply is NO way you can have full free flow, good sound outside, and minimal sound inside... everything we've tried has only marginally reduced the sound inside, or has restricted the flow... i think we should just email MS to get them to change the freakin design!!! hahahahha! but that's just my opinion!

 

There is no way to stop things from vibrating.
Things vibrate because they are.

The mazdaspeed have to short a silencer to handle waves under 115Hz (3450rpm) Proof is, over 4000rpm(133Hz) things are dead quiet. (almost)

So on for the resonator, like the MS it share from it's flenge to it's end the same 28inchs, what abouts 2 tuning forks???

BBwoulf experiment show it's possible to lower the frequency to a level were the cabin do not resonate and for me it's a succes... Proof that a no brainer formula work.

P5freak experiment show how to kill a pressure wave where it appear, is baffle style plug returne the pressure wave so it cancel out.

silver_p5

Im not a sonic specialist i'm not even a scientist.
In my first post i give some links I hope that will help you.

 

HOLD EVERYTHING!!!!

I've f#@$@ked up my working experiment...

Today (Sunday), I finally got the plug out of the exhaust. Horraay!!

WRONG!!!

I cut the angled piece of the exhaust off because I felt it was contributing to turbulance (turbo wastegate noise at high rpms).

I then went to put it back in and.... yes, you guessed it!

It fell into the muffler, it no longer pinches into the metal.

The ID of the outlet of the muffler is 2". The OD of the restrictor is 1 7/8".

You can order that $28 dollar part and it will work, but it is just pinched in there . My wife says "Why can't you just leave things alone!". I guess it's in my blood to make things work right, not bandaid it.

Anyway, tomorrow I am going to stop by a welding shop and chat about somehow (wrapping metal or something) taking the OD of the restrictor from 1 7/8" up to 2" and tapping it back in place and securing with a stop screw.

Hang in there fellas we're in this for the long haul.

Bigbadwolf - Excellent experiments! I'm also contemplating a 2' 2" OD exhaust pipe going right through the muffler. It doesn't resonate with the muffler off so why not bypass it by not making it get worse by entering the chamber?

 

Today's Update (Monday Morning)

After screwing up my quiet exhaust I dropped it off this morning at a metal fabricator to have it wrapped in stainless to get the OD back to 2". It's going to cost $45 which blows but I want to do this right. If I do it using regular steel or exhaust tubing to get the OD up to 2" and it works, you know it will rust away.

I'll have an update either this evening or tomorrow.

 

Today I discovered the mind-altering, body-bending aftereffects of Monday heaped on top of a supreme sub-sandwich and Doritos nacho cheesier induced recliner coma. Whoa.

I also discovered that some muffler shops aren’t much help when it comes to dealing with stainless.

P5Freak –

Sorry to read about your plug discovery – sounds like something I’d find. I’m doing about the same thing with the second stage of the pipe insert development – I’ll be talking with a metal fabricator tomorrow. I’ve worked up a sketch for a stainless pipe with a ˝” wide ring welded on the tip-end for better support and sealing, plus it’ll give me an attachment point once it’s drilled. Also, I’ll have them chamfer the muffler-end of the pipe for an improved seat and seal. After a little sandblasting, it should blend with the rest of the exhaust pretty well. I'll just have to see what it'll cost...

Heads-up – Wednesday is a Full Moon!

 

Well I've gotten to where I have actually quieted it down inside the cabin. The fix concerns modifying the rear heatsheild over the muffler. I drilled out the 4 rivets and removed it. Due to time constraints I had to reinstall the pipe with out the sheild in place. MUCH louder! Went to Pep Boys and bought 2 cans of Wesley's undercoating and some big *** replacement rivets. I took the pipe off again and thouroughly undercoated (3 coats) the floor board area and frame rail where the muffler can sits. I also did the same thing to the top of the heat sheild (the side that faces up, not the side that faces the muffler). After it was fairly set I adhered 1 strip of neoprene rubber the the top in the middle to act as a buffer between the sheild and the floor (about 3/4 inch thick x 1.5" x 3"). I re-riveted the thing back into place, having to use some backing washers inside the car because the holes got elongated by my drilling the originals out. With pipe back in place I went for the usual test run. To my surprise it seemed much quieter, still there, but not so boomy and intrusive. The ultimate test was taking wifey for a ride. She had almost gotten to the point where she did'nt want to ride in the car anymore. Her verdict.... "substantial improvement, now it doesn't sound like a clapped out pickup without a muffler, it sounds like a sports car". I was glad to hear that because I've gotten to the point where I think I could convince myself of anything concerning this issue. Plus the pipe's been on and off the car more often than a trailer queen's prom dress and I'm tired of experimenting. I'm gonna have to wait a few days and see if things change as the undercoating sets up more. It was pretty damp when I reassembled and test drove the car. So far, so good.

Jeff M.

 

Nice work silver_p5_owner!

My issue is worse. My P5 IS my wifes car. The worst you could get is "We aren't taking your car". The worst for me is "I hate driving that thing! Why can't you just leave things alone?!" - my wife.

I can't really blame her though. We also have a 9mo. old boy that doesn't need to put up with it either.

My wife loves driving my CRX Si (full catback exhaust -n- intake). Go figure.

My plug (once modification is complete) takes away all of the pain yet leaves a noticable bark outside the car.

I will provide a new full set of instructions/photos for my fix once I get the part back from the metal shop.

Off the record...

This has been one of the most enjoyable conversations. You guys rock!!

 

Perhaps it was the soft red Italian wine I drank with supper to contrast the mildness of the mozzarella and the boldness of a “robusto” dressing on my freshly tossed salad, or perhaps it was the rubberized undercoating/sound deadener I sprayed around the exhaust area, but the MazdaSpeed seemed a little mellower during a trial run this evening.

Good job silver_p5_owner! The "rubber coated tuning fork" approach isn't a bad one and this seems more effective then trying to deaden the sound from the inside of the car. And I had to LOL about you taking off the exhaust so many times - my neighbors have started to think it's part of what I have to do before putting my car cover on each evening.

I’ve faxed my pipe insert sketch to the metal fabricator today, so I hope to know something about cost and delivery tomorrow. I’m interested to try this because of the refinements over the black iron pipe – additional support of the pipe on the tip end and better sealing on both ends. Also, I’m making this insert about a ˝” longer to 6” even.

P5Freak - compliments to you for starting the thread!

 

guys whats bad with leaving the 5" pipe in. Will it rust??? I thought those pipes are weather resistant.. I thought those black pipes are used for water. Just wondering I got in my exhaust and don't like the drone at all. I tried the pipe and I can defintely tolerate the sound now. Better on my ears.

Thanks

RC

 

Cruzer, I'm afraid the iron pipe will eventually rust in the exhaust. It's exposed to condensation as well as a witch's brew of chemicals with a range of pH's that'll start to oxidize it after a while. That's why stainless is the best choice for a long-term application.

 

Well, as things still seem to be pretty loud I re-analyzed the situation with the heat shield and decided to to coat the underside. Seeing as there is about 2 inches clearance between the muffler can and the heat shield and the big can does not seem to get too hot, I undercoated the downward face of the heat shield also. Wow, what an improvement!! I would have no concern letting everybody concerned about a noise problem with the sport exhaust using a lot of undercoat in the body cavity and both sides of the rear heat-shield. I was amazed when I coated the top side, now I am ecstatic about the results with both sides coated! Of course anyone has to do this at their own risk, but I am thrilled with the results! I may not need the pipe extension after all!

Jeff M

 

silver_p5_owner,

can you post up some pics of what you did.

Thanks.

RC

 

[Cruzer]

Can you post a picture of your rear exhaust? I would like to see what it looks like with the MP3 rear skirt. How is the clearance?

 

sure no problem, just have to wait until I get home..