Tips on quieting down my exhaust?
 

I've been researching on how to quiet down the exhaust on my car. I wanted to see what everyone else has deployed to bring it down to a manageable level.

Currently I just have the Racing Beat dual tip muffler but I'm looking into adding a large Magnaflow oval muffler under the car. I'm open to other solutions as well!

Thanks,
Aaron

If you have a straight midpipe, then yes, the resonated midpipe will help.

This is a v-banded setup so I'm wondering what mufflers/resonators to weld in to place.

Get the magnaflow oval style cannister and your noise volume will decrease a large amount. If it's still too loud, wrap as much piping as you feel like in DEI Titanium heat wrap :)

Borla: http://www.borla.com/products/xr1.html

My opinion is, goto a well know exhaust shop that actually work on performance cars.

Tell them your needs, pick the brain of the "main" guy behind the counter or at the shop.

They'll open up when you ask nicely. Hell they can even get metallic cats that's not even "allowed" in the state of CA for me ;-).

I will update my setup once done by end of this week and I will let you know the end result/sound.

Currently I have V-band set up from turbo to downpipe. Gonna have the shop weld a Metallic cat + resonator on the mid section and Greddy Full-Ti exhaust.

-AzEKnightz

You might keep an eye on that cat. Even some of the more well known metallic cats have failed quickly on rotaries. I would ensure that you use a proven metallic cat when making that choice rather that what "something can find".

Yes, that's exactly why I spoke to the owner. Who is also a mechanic there. Be in this industry for over 30 years.

I asked him what type of cat should I put in it. He said, THERES only a couple will work due to high exhaust temp. After speaking to him, as I am a mechanic myself. He know what he's doing and he's well aware of the situation.

Then he quickly proceed to search the right one for me. While he was searching, he said "you know, the cat you need is not legal in CA and I 'might' get a hand on one."

Knowing the fact that he's straight up told me what's going on and best super honest. I will trust me. Because he said he will warranty it too. Win win for me!

-AzEKnightz

Thought the RB dual tip was as quiet as it gets next to stock.

It's only going to be so quiet when you remove the stock catalytic converter in favor of a cat-less/muffer-less midpipe.

Go with this:

Resonated Midpipe 93+ RX-7

I've got this on my 20B and it works great. Car is very quiet. Money well spent.

^^^ I have that one and my car still loud lol. But my muffler doesn't help

The tanabe medalion touring exhaust is extremely quiet. Sounds just like the stock exhaust, granted I only have a PR down pipe and this exhaust.

The noise problem in a rotary is bifold, we have high rates of pressure change from ports instead of smoother cam operated valves in a reciprocating engine (think square wave pressure graph instead of sine wave). The second issue is the environment, high vibration and heat.

The science behind noise reduction has three main approaches: resonance elimination, insulation, and absorption.

Resonance is the rhythmic vibration that makes parts essentially turn into speakers. At idle, a ported rotary on a lightweight and rigid 3 inch exhaust just drums away with a sharp note. If you knew the wavelength of that energy, you could make or install a muffler with half the wavelength of the sound, or with chambers of half the wavelength of that sound. This would create destructive interference and greatly reduce the energy emitted at that wavelength after the reduction, and solve your idle noise, and not do much at other wavelengths. Installing two of these same tuned mufflers in series would do very little more to cancel the energy at this frequency more. Tuned mufflers cancel resonance. Using several of different sizes and types can work very well.

Sound absorption is accomplished when you have energy being imparted into materials that are self damping, like foam. Fiberglass packing can help with this, but our hot rotaries are good at burning it. Stainless packing helps too. Effective absorbtion takes tons of volume/space and isn't practical.

Sound insulation is accomplished by putting barriers and controlled volumes of air between the resonant source and the sensor (you). This is also not very realistic.

The enemy of speed is the ally of sound deadening- weight. In the right place, weight addition can modify the natural frequencies of your entire exhaust system, floor boards, and inner fenders. We remove the heavy this exhaust with its many bends for thinner and lighter higher flowing straight units with potentially terrible noise and resonance properties.

So what is the best balance? A good variety of mufflers/resonators on a full length exhaust system that isn't too large of diameter. The longer path the better. The Farther upstream you can put the first resonator, the better for sound (not too close, you want spool, right?).

Turbos make excellent sound reducing devices. I'm assuming you are turbo.

I'm running 3 inch steel pipe on my FD, with 2 different very free flowing resonators and two similar not straight-through mufflers that flow well and are not the same size. Everything is in line. No big polished exhaust tip, just a 3 inch turn down. No cat. Recirc WG on a T61 with a big divided manifold. Should scream... It raps a little at idle and is damn quiet until it is wide open and above 5k. Highway drone is completely gone. I am sure I gave up some spool time and a few HP, since my setup isn't perfect. But it is quiet and it was less than $400 from the turbo to the tip.

Hope at least one of you enjoyed the read. :)

I had 2 oval magnaflow on my 4" exhaust with the last 20b and it was much quieter that my current dual oval borla 3.5" exhaust

Aaron--you, with a quieter car??? man I think we're both getting old...

dumb question: you've recirculated your wastegate right? RB is quiet. The fact that you are saying it's still too loud makes me think you have an open wastegate. Or you need to sell the FD and get a stock M5 :lol:

What brand/type did he recommend?

Bonez makes a good, proven hi-flow cat for the FD.

Man, on my old 2002 BMW E39 M5 V8, I cut everything off at the headers and ran two 3 inch pipes from there to the rear bumper, only merging them into a twin inlet/outlet resonator halfway down. That thing was loud. Louder than my FD could ever be..

Stainless glasspack muffler, or something like a Hooker Aero Chamber muffler with its internal baffles, would cut the noise down a lot.

I'm not sure if it's that I'm getting older or I want the car to be a sleeper again. It used surprised everyone before I had it painted, but now it's becoming anticipated. I want to throw everyone off again with a super quiet car. Not to mention, I can't race the car without ear plugs for any extended length of time.

I'm also working on raising the quality level on the entire car up a notch. The entire suspension and drivetrain has been rebuilt and I'm working on making everything look as if it came on the car. I'm probably not going to make it to a Gmonsen level but I'll at least bring it to a clean low mileage stock level.

resonated mid pipe is the way to go as everyone suggested, mine is still loud to my taste when idle when I have resonated mid pipe and RB duels, but then again I am running a ported motor after all.

Roguefab,

What type of resonators do you recommend, sir?


Aaron

[QUOTE=Dabossajk;11465122]Roguefab,

What type of resonators do you recommend,



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