Free flowing AND quiet: CAN YOU HAVE BOTH?

[Meat coyote racing]

Hello all,

Does anyone know of an exhaust setup that is quiet but simultaneously free flowing? My initial thought is no, not possible. The only setup I can think of is a Roush active exhaust kit.

The problem: I'm being stationed in Germany. To drive on German roads you have to pass a thorough inspection which only allows 95 decibels at 4k RPM, measured at a 45° angle from around 5 feet away.

My setup:
2017 GT
Gen 3 Whipple stage 2
1 7/8 LTH catted
X pipe with roush axle backs
(So loud it would wake the dead)

I did testing with a Borla touring resonator with Roush axle backs and reached 114 decibels. I THINK with the stock mufflers welded back on, it might bring it down to 95 decibels, haven't tried yet. The resonator is necked down to 2 1/4 inch, is chambered and restricts flow. I could throw everything on (borla, stock mufflers) pass inspection, take everything back off and cross my fingers I won't get stopped by German police. However, it would be nice to have an exhaust system that could wear both hats and be quiet and free flowing.

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[kent0464]

I’ve been thinking about this myself. At 55 yo I still like to hear the engine but my Borla with no resonators is entirely too loud, can’t even enjoy my aftermarket stereo w/ 1200+ watts.....
I’ve lifted 2 of the quietest fairly high power cars that I know of to take a look at how they accomplished it, the 350z and the 370. I will probably try to copy their set up if I keep the GT.

 

[Ebm]

Hello all,

Does anyone know of an exhaust setup that is quiet but simultaneously free flowing? My initial thought is no, not possible. The only setup I can think of is a Roush active exhaust kit.

The problem: I'm being stationed in Germany. To drive on German roads you have to pass a thorough inspection which only allows 95 decibels at 4k RPM, measured at a 45° angle from around 5 feet away.

My setup:
2017 GT
Gen 3 Whipple stage 2
1 7/8 LTH catted
X pipe with roush axle backs
(So loud it would wake the dead)

I did testing with a Borla touring resonator with Roush axle backs and reached 114 decibels. I THINK with the stock mufflers welded back on, it might bring it down to 95 decibels, haven't tried yet. The resonator is necked down to 2 1/4 inch, is chambered and restricts flow. I could throw everything on (borla, stock mufflers) pass inspection, take everything back off and cross my fingers I won't get stopped by German police. However, it would be nice to have an exhaust system that could wear both hats and be quiet and free flowing.

First step is getting rid of the X-pipe, Roush ABs, and LTHs. I would recommend stock mufflers or even GT500 mufflers from a 2011-2014 Mustang GT500 would work. If you don't want to get rid of the LTHs, you'll need a bigger muffler(think suitcase).

The Roush ABs aren't really adding anything over stock except the sound. A suitcase muffler still flows pretty well, but you'll see a small horsepower loss. This is a tough question because it doesn't come up much lol. Good luck with whichever direction you go!

Also, I will say that a turbo setup would have been quieter without making any changes. But I doubt you want to switch from a blower to a turbo as that's $$$$.

 

[Meat coyote racing]

First step is getting rid of the X-pipe, Roush ABs, and LTHs. I would recommend stock mufflers or even GT500 mufflers from a 2011-2014 Mustang GT500 would work. If you don't want to get rid of the LTHs, you'll need a bigger muffler(think suitcase).

The Roush ABs aren't really adding anything over stock except the sound. A suitcase muffler still flows pretty well, but you'll see a small horsepower loss. This is a tough question because it doesn't come up much lol. Good luck with whichever direction you go!

Also, I will say that a turbo setup would have been quieter without making any changes. But I doubt you want to switch from a blower to a turbo as that's $$$$.

For the inspection, I think I'm going to put on the Borla touring resonator and weld on the stock suitcase mufflers and measure the sound level. If its still too loud, I might stuff the muffler with steel wool and see if it quiets it to the level I need.

I think the answer might be, pass inspection and put on a roush active exhaust and close the valves if I'm in a city or pass cops. The only reason I'm changing anything is for the stupid inspection.

 

[Ebm]

For the inspection, I think I'm going to put on the Borla touring resonator and weld on the stock suitcase mufflers and measure the sound level. If its still too loud, I might stuff the muffler with steel wool and see if it quiets it to the level I need.

I think the answer might be, pass inspection and put on a roush active exhaust and close the valves if I'm in a city or pass cops. The only reason I'm changing anything is for the stupid inspection.

Sorry you are having to jump through hoops. It's crazy how lenient the US is for safety and emissions and car road use. We are one of the only countries where you can lift your truck as high as you want or have your car as loud as a Nascar stock car. It may technically not be legal in many states here, but it isn't enforced either.

 

[Zelek]

Corsa Sport + Vibrant 1794 resonators + Catted headers = a very tolerable solution. Some people can't even tell I barely have exhaust at idle. Different story at 5k rpm. May be what you're looking for. It takes a lot of resonating and decent mufflers to bring the volume down.

I'm about to switch to catless + Krona catback here soon so my volume is going to increase for sure. I'll likely sell my Corsa setup once I get it on the car.

 

[CrashOverride]

Since you say you're being stationed in Germany, that sounds to me like you are in the armed forces. If you are, thank you very much for your service - I'd shake your hand and buy you a beer if I could. Getting to your question though, any perforated pipe muffler will give you full flow and reduce noise. Some perforated mufflers use an internal pipe larger than the input pipe (e.g. a 4" pipe inside the muffler that has 3" inlets and outlets) and that's how they can rightfully state they flow better than a straight pipe.

The diameter of the pipe affects noise as well - you get to a point where adding diameter doesn't really affect flow much more, even though it gets louder.

I keep messing around with my exhaust to get what I want, and at one point I had an x-pipe and Rousch axle backs. I loved the sound, but it was far too loud and got me the kind of attention I didn't want. What I would suggest is this: Go with a perforated pipe X-pipe. Dynomax, Magnaflow and Borla all have this style. There are even some Amazon cheap knockoffs that have this. The larger the case, the more sound it attenuates. There is probably enough room to install two longer case units before it jumps around the axle. Doing this, you would kind of have a corsa-like X-pipe (Basically with two crosses) but be muffled. From there, if you were willing to spend a little bit of money to make your life easier, I would have an installer weld up a nive v-band clamp right after the axle, and then weld you up two more perforated-tube mufflers. Going with a larger body will help. That would be the set you keep on your car all the time. I'd then have your welder weld you up another set of cheap perforated tube knockoffs -- but -- have the welder weld-in a block off plate. Imagine welding in a piece of plate steel at the beginning of the muffler, then drilling it out, say with a 1.5" hole saw. When you hook that up to your v-band clamp, it will look completely normal, yet be much quieter. Do the inspection, unbolt the v-band, swap out for the non-restricted mufflers, and be good to go. It will still be significantly quieter (You'd basically be running 4 mufflers) but because the entire system was perforated tube muffled, you will have almost no restriction.

If you have your car tuned by a tuner, you can reduce the volume by taking some of the overlap out of the cams -- but that is an extreme tweak, and I'd re-do the exhaust before doing that.

Do us all a favor and hit the Autobahn for us, and take one trip around "The ring" as well. Aufwiederschreiben! (I'm part German, and speak a very very tiny amount).

Stay safe out there

 

[GregO]

However, it would be nice to have an exhaust system that could wear both hats and be quiet and free flowing.

https://www.millteksport.com/products/ford/mustang.html?resonated=14

 

[2017ArizonaGT]

First post for me, so woo hoo!
If you are running 2.5" pipes, I have an RTR Tactical Street-Spec axle-back and absolutely love the sound. It is more smooth than stock, deeper tone, nice and mellow at idle and driving around with a nice civilized growl when you get into it. Also, although it might take some tweaking to fit, but CJPonyparts has a magnaflow tru-X resonator that utilizes 2.5" pipes (inlet is necked down to 2.25" but can be cut) that should really calm the noise down but flow really well. Something to look into.
Kevin

 

[ManBearPig]

Longubes and factory catback should do the trick

 

[BmacIL]

MF resonated X-pipe and 11-12 GT500 mufflers would be pretty quiet, as would the FP by Borla Touring axleback with the same MF resonated X-pipe.

 

[DeCo]

What about X Force Varex, either the Catback which has a resonated x pipe and valved mufflers, or you could weld in just the mufflers, not sure if that would get you to the level you need. They also sell an engine back system with headers and cats. Both the Catback and engine back systems are 3" piping. X Force is an Australian company, and appears to have an EU division. It is not a cheap solution but I have been looking into it. With the new Smartbox you can set it up to change the exhaust to close by GEO location, there is also a "Matrix" mode where you can set it by RPM, throttle, speed, ect. I am thinking of going with the Catback for now then maybe add the headers Later to spread out the expense.

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