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Discussion Starter · #1 ·
Hi all,

I've been considering going the custom route for an exhaust as I already have my resonator deleted and am mainly looking for a more aggressive sound, not volume.
I've noticed most threads here involve straight through mufflers in the location of the resonator.

My question is, has anyone tried to mimic the stock location with a larger muffler just like the Ford Performance / Borla does?
It seems like many members here enjoy their straight through style custom exhausts, though I would prefer the sound of a chambered Flowmaster.

I have a wonderfully illustrated mock up below with approximate measurements comparing the stock and Ford Performance to my Flowmaster idea:
Does anyone see any issues with this idea? Am I missing anything?
391619


Thanks in advanced!
 

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This is absolutely something a good exhaust shop is capable of! I'm Interested in hearing a video when it's finished.
 

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Discussion Starter · #3 ·
This is absolutely something a good exhaust shop is capable of! I'm Interested in hearing a video when it's finished.
Good to know! I would absolutely post a video. (Don’t worry, I won’t stick the microphone 2” behind the bumper) I know Flowmaster videos on STs are far more limited, especially custom setups.
 

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If you have to fab it up I would put the flowmaster right after the down pipe and fab a smooth bending exit for my tips and keep in clean in the rear. Either way the flowmaster 50 will sound nice and loud.
 

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I would also use the configuration of: offset inlet and center outlet.
This will better mimic the stock muffler format.
 

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Discussion Starter · #7 ·
If you have to fab it up I would put the flowmaster right after the down pipe and fab a smooth bending exit for my tips and keep in clean in the rear. Either way the flowmaster 50 will sound nice and loud.
When I get under the car I'll look and see how much easier it'd fit in that spot, I thought the full chambered muffler would be too large for the opening.
I'll definitely report back with an update / video when it's all done.

That's what I'm thinkin, this muffler should sound really good even though the super series is more restricted than the others.
 

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Discussion Starter · #8 ·
I would also use the configuration of: offset inlet and center outlet.
This will better mimic the stock muffler format.
Thanks for the suggestion!
My buddy who is helping me weld suggested offset for both sides to keep things as quiet as possible, I'll look for the center out if it would help the orientation of the piping.
 

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Discussion Starter · #10 ·
I've just ordered the parts and thought I would offer an update as far as my virtual mock-up goes!

Muffler is a Flowmaster Super 50 Series (listed as an SUV muffler on Summit racing). Inlet is off-center, outlet is center (thanks for the suggestion @SSgtjrobertson!)

Tips are just plain old Flowmaster dual tips, 2.5in inlet, 4in dual out:

Besides that, it's just stainless piping, we'll figure out the hanger situation day-of.
391703
 

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Definitely like the direction you're heading. As a warning however this muffler has zero packing. It relies solely on a series of internal chambers and baffling. It is primarily used up stream in the exhaust system for sound cancelation.

391704


This design will have some droning at a fixed RPM range. I couldn't tell you where but rest assured that it's going to be where you don't want it because that's how it always works. LMAO!

Some of this drone can be reduced (not eliminated) by integrating a helmholtz resonator into the end.

391705


Extending the outlet pipe out past the tip and capping the end off will function as a 1/4 wave (helmholtz) resonator. Drill your tip into the outlet pipe at 90 degrees. You can do this easily with a hole saw. Don't be afraid to shorten up the tip length. To meet your needs.

If you don't have a welder you can usually mock everything up and find a local person to finish the parts off for you.

Stay Safe
J
 

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Discussion Starter · #12 ·
Definitely like the direction you're heading. As a warning however this muffler has zero packing. It relies solely on a series of internal chambers and baffling. It is primarily used up stream in the exhaust system for sound cancelation.

View attachment 391704

This design will have some droning at a fixed RPM range. I couldn't tell you where but rest assured that it's going to be where you don't want it because
that's how it always works. LMAO!

Some of this drone can be reduced (not eliminated) by integrating a helmholtz resonator into the end.

View attachment 391705

Extending the outlet pipe out past the tip and capping the end off will function as a 1/4 wave (helmholtz) resonator. Drill your tip into the outlet pipe at 90 degrees. You can do this easily with a hole saw. Don't be afraid to shorten up the tip length. To meet your needs.

If you don't have a welder you can usually mock everything up and find a local person to finish the parts off for you.

Stay Safe
J
That’s a great idea! I didn’t think of doing the j tube, kind of looks like the MRT axle back. I’ll see what I can do to find the right tube length. I know there’s a way to calculate quarter length.

Although the muffler is chamber style, Flowmaster claims this one in particular will have very little interior resonance, being the 50 series and the quieter of the two. Maybe what they really mean is in comparison to the louder ones like the 40 series. Also, like you said, they could imply that its positioned upstream.

Not sure if I could consider another position with a chambered muffler like this, but either way it seems like the j tube will offer the most help in reducing drone. I also have my entire spare tire section stuffed with foam and sound deadening material, I experience zero drone right now with the resonator delete, might help my cause as well.

Thank you again for further insight!
 

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As a side note this is the direction that I will be ultimately heading.

Vibrant makes a universal muffler that doesn't require directional input or output.
391707


So this will leave me with a one 2.5" input. One 2.5" helmholtz resonator port, and a single 3" center output the I will neck down to whatever I feel is appropriate to maintain flow and decible levels. However I'm roughly a year or so from this project.

J
 
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Calculating helmholtz is a fairly complicated matter since items like exhaust gas temperature are massively dynamic. What you can do, though, is build an adjustable one with a lap-style sleeve clamp and two varying sections Of pipe (one can just slip over the other) so the length can be adjusted, which can help you fine-tune it based on real world drone range.

This can always be added to the location that ssgtjrobertson pointed to after the exhaust has been made. So you can start with that exhaust and determine if you even need one to begin with (which, you probably Will, but this is an exhaust that nobody has run before, so thats completely speculative).
 
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Completely agree with @TurboGT .

The key to remember is that the Helmholtz resonator cancels drone at a particular frequency and will cancel it after it's installation point.

So the non enginerd quick and dirty method is to install the Helmholtz resonator as far forward in the system as possible. When in doubt make it as as long as you can without it interfering with the rest of the system or vehicle.

In cabin drone is what most people are trying to avoid normally, but remember that you aren't limited to a single one in the system.
 
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Discussion Starter · #17 ·
It will certainly be interesting to see what frequencies I need to cancel out, like @TurboGT said all this is speculative.

I like the idea of making the resonator adjustable.
With the sleeve clamp set up, should I use 3” pipe to slide over the 2.5”?

@SSgtjrobertson that vibrant muffler looks killer by the way, excited to see your project when you get started.
 

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It will certainly be interesting to see what frequencies I need to cancel out, like @TurboGT said all this is speculative.

I like the idea of making the resonator adjustable.
With the sleeve clamp set up, should I use 3” pipe to slide over the 2.5”?

@SSgtjrobertson that vibrant muffler looks killer by the way, excited to see your project when you get started.
I'd use 3" inside diameter with 3" outside diameter, or 2.5" inside with 2.5" outside diameter.
 
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That’s a great idea! I didn’t think of doing the j tube, kind of looks like the MRT axle back. I’ll see what I can do to find the right tube length. I know there’s a way to calculate quarter length.

Although the muffler is chamber style, Flowmaster claims this one in particular will have very little interior resonance, being the 50 series and the quieter of the two. Maybe what they really mean is in comparison to the louder ones like the 40 series. Also, like you said, they could imply that its positioned upstream.

Not sure if I could consider another position with a chambered muffler like this, but either way it seems like the j tube will offer the most help in reducing drone. I also have my entire spare tire section stuffed with foam and sound deadening material, I experience zero drone right now with the resonator delete, might help my cause as well.

Thank you again for further insight!
These are all good ideas for you to consider. Consider building it according to your original layout, above, and then run it to see if you need a resonator in the first place. If you do, then consider locating it ahead of the muffler. Vortex shedding generated by gas flow past the sharp edges of the branch pipe can produce high-pitched noise, but this turbulence can also induce self-excited resonance in the tube, reducing its overall efficiency. A muffler can attenuate some of this noise if it occurs (providing a radius or chamfer at the resonator tube entry can also help). Sound-dampening material in the car will certainly help.

As already mentioned, exhaust gas temperature is a critical factor, and it must be measured under a load and within the rpm range where droning occurs. Adding a threaded bung to the exhaust pipe to accept an adapter for a temperature sensor will make it fairly easy to do this. Measurement can be taken from inside the tailpipe, but this will be less accurate. Another critical factor will be frequency. The best way to figure this is with a noise meter, and apps are available for Android and iOS that can perform a frequency analysis. A less accurate alternative is to calculate firing frequency, based on the rpm range where droning occurs.

If you record a frequency spectrum of the exhaust under drone conditions and the dominant peak in the spectrum is centered at 80 Hz (and this corresponds to the dominant peak in a spectrum recorded in the cabin under the same conditions), then this is the target frequency you want to tune for.

Making the resonator adjustable is a very good idea, but it should be possible to get the length pretty close by careful attention to detail, even when using simplified acoustic theory instead of 1-dimensional analysis or finite element method.

I've been working on a writeup on drone and resonators for the forum and plan to post it some day, whenever I have time to finish it. I'll include the summary to that piece here, in case it might be of some use. I've appended a paragraph from the main text on the effect of a tailpipe and its length between a silencer and the atmosphere.
 

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