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Discussion Starter · #21 · (Edited)
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.
Thanks for all this info!
I’m pretty sure I’ll start with the original build and reassess once it’s on there.
 

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I'll probably end up with the Ford performance exhaust. Before that happen, I will experiment with the stock exhaust. There is a modification I had seen on Porsche 911. They add a bypass to the muffler. It add a little free flowing to an otherwise stock muffler. The ST muffler is a very restrictive design. It is not a thru flow muffler ,but it can be modified. If you follow the line of the intake pipe to the other end, it end short to go thru. If you make a hole and introduce a reducer that will stick out, weld around and them two 90's it will connect to one of the two original exhaust pipes with a 45. you will have a thru flow muffler with two additional exit. You can add a cut off to open and close the new passage.
 

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@STallion18 looks can be deceiving. Our mufflers actually Flow pretty well even at higher HP levels. The downpipe is the main exhaust bottleneck.
 

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Discussion Starter · #24 ·
@STallion18 looks can be deceiving. Our mufflers actually Flow pretty well even at higher HP levels. The downpipe is the main exhaust bottleneck.
Isn’t it also true the stock turbo’s threshold is not far off? I know the downpipe allows for stage 3, but I’ve read here the throttle response is really what’s noticeably different before running a bigger turbo.
 

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Discussion Starter · #25 ·
I'll probably end up with the Ford performance exhaust. Before that happen, I will experiment with the stock exhaust. There is a modification I had seen on Porsche 911. They add a bypass to the muffler. It add a little free flowing to an otherwise stock muffler. The ST muffler is a very restrictive design. It is not a thru flow muffler ,but it can be modified. If you follow the line of the intake pipe to the other end, it end short to go thru. If you make a hole and introduce a reducer that will stick out, weld around and them two 90's it will connect to one of the two original exhaust pipes with a 45. you will have a thru flow muffler with two additional exit. You can add a cut off to open and close the new passage.
I like the design, much cleaner mock up than my Microsoft paint skills lol. I would’ve done the FP as well if I was concerned with going full stainless. Out here in Seattle we don’t deal with salt so I’m not too worried about mimicking it with my preferred muffler.
 
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I like the design, much cleaner mock up than my Microsoft paint skills lol. I would’ve done the FP as well if I was concerned with going full stainless. Out here in Seattle we don’t deal with salt so I’m not too worried about mimicking it with my preferred muffler.
I'm in south/central TX, road salt is not a problem. I liked the sound and look on the Octane Academy cars with that exhaust. I just like to fabricate, if I don't like how it sound after the mod, I will just get the FP exhaust.
 
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Isn’t it also true the stock turbo’s threshold is not far off? I know the downpipe allows for stage 3, but I’ve read here the throttle response is really what’s noticeably different before running a bigger turbo.
Yeah, thats true. On stock tune i noticed power carry a little higher in the rpm range with the downpipe. And yes, the turbo is Already being pushed beyond it's limits stock, anything beyond that is severely over-driven. Which is a testament to that turbo, considering How many ST guys tune them and run the crap out of them.
 

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Discussion Starter · #28 ·
Yeah, thats true. On stock tune i noticed power carry a little higher in the rpm range with the downpipe. And yes, the turbo is Already being pushed beyond it's limits stock, anything beyond that is severely over-driven. Which is a testament to that turbo, considering How many ST guys tune them and run the crap out of them.
Makes sense. I’m dailying on Stage 2 but only drive hard on occasion. After the Flowmaster project, I’ll keep this exhaust and tune as is until I’m ready to size up the turbo.

In a couple of years I hope to daily a truck, granted manufactures can finally order chips and the cost of all vehicles aren’t inflated as can be lol.
 

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Discussion Starter · #30 ·
Piping won’t be here until the end of the month, but Summit shipped the muffler and tips extremely fast!
Here’s a peek at what I have so far:
391783
391784
 

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Usually my thoughts with respect to these DIY engineering projects tend toward "many professional engineering companies have already solved these problems" but this project looks like it is taking math and science into account, and will cost half of what Borla et al charge for what looks like a similar system. Plus- you are doing this yourself- which adds quite a bit of value in my mind. Great job so far, and best of luck; I am definitely interested to see how this turns out!
 

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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.
Or a young inexperienced welder in my garage 😂

Not the prettiest welds but don't really care since it's not something I'm going to look at. Used a mix of off the shelf 3" bends from Jeggs and what we cut off the existing 3" that was there.


Used this muffler: https://www.amazon.com/gp/aw/d/B000COP64Y/

Just trying to get a quieter exhaust when on the hw mostly. Still sounds good and I have an open wastegate for loudness when I'm in boost. It's all 3" and straight through on top of the 3" Fswerks stealth exhaust (magna flow muffler nearest the dp and then a magna flow resonator before the subframe
 

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Discussion Starter · #33 ·
Or a young inexperienced welder in my garage 😂

Not the prettiest welds but don't really care since it's not something I'm going to look at. Used a mix of off the shelf 3" bends from Jeggs and what we cut off the existing 3" that was there.


Used this muffler: https://www.amazon.com/gp/aw/d/B000COP64Y/

Just trying to get a quieter exhaust when on the hw mostly. Still sounds good and I have an open wastegate for loudness when I'm in boost. It's all 3" and straight through on top of the 3" Fswerks stealth exhaust (magna flow muffler nearest the dp and then a magna flow resonator before the subframe
Not bad! Yeah I’m not concerned with what it looks like under there either, as long as the tips are aligned. Did you weld the section that runs in front to the muffler as well?
 

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Not bad! Yeah I’m not concerned with what it looks like under there either, as long as the tips are aligned. Did you weld the section that runs in front to the muffler as well?
Everything in that picture is one piece. There is a slip joint right before the sub frame, the existing one from the Fswerks setup. It's not too bad to take the section off as one by myself
 

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Discussion Starter · #35 ·
Everything in that picture is one piece. There is a slip joint right before the sub frame, the existing one from the Fswerks setup. It's not too bad to take the section off as one by myself
Oh I see, I like how the piping really extends to the passenger side before being routed back toward the center.
I know it wouldn't be the same effect of the helmholtz resonator, though it looks like may it help with some of the interior sound.

How is this set up for you? Does it limit the interior noise / drone?
 

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Oh I see, I like how the piping really extends to the passenger side before being routed back toward the center.
I know it wouldn't be the same effect of the helmholtz resonator, though it looks like may it help with some of the interior sound.

How is this set up for you? Does it limit the interior noise / drone?
yeah that big 180° bend was more of a means to an end, only way I was gonna fit the muffler, the offset in/out of the muffler helped (magna flow says it didn't matter which way it flows.) I thought about doing a helmholtz but that would involve maths and probably much more trial and error. It also sounded like, from my readings, it would be more effective further from the exit.


It could still be quieter inside for longer trips but probably as good as Im going to get without adding a cat. I have my trunk/hatched fully lined and my doors about 50% in dynamat. I'd have to go with some fatmat or other thicker/heavier stuff if I want it actually quiet in the cab.

The muffler helped but it wasn't as dramatic as when I added the stealth/resonator section. Before that, the drone was terrible, had to practically shout to hear the person sitting next to you
 

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Or a young inexperienced welder in my garage 😂

Not the prettiest welds but don't really care since it's not something I'm going to look at. Used a mix of off the shelf 3" bends from Jeggs and what we cut off the existing 3" that was there.


Used this muffler: https://www.amazon.com/gp/aw/d/B000COP64Y/

Just trying to get a quieter exhaust when on the hw mostly. Still sounds good and I have an open wastegate for loudness when I'm in boost. It's all 3" and straight through on top of the 3" Fswerks stealth exhaust (magna flow muffler nearest the dp and then a magna flow resonator before the subframe
Those welds don't look so bad. All in all, your addition looks like a pretty sanitary arrangement.
 

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I have my ST up on the lift to change oil, install a Mountune BPV and perform an overall wellness check, and this is a picture of my Borla exhaust after having been on the car for just about 2 years. This is my DD, and I do not specifically clean the underside of the car, although I do rinse the underside with a lawn sprinkler after driving the car in the salt/snow. I know Borla manufactures their systems using 304 austenitic stainless steel, and while you do not usually see this part of the car, it still looks like it did the day I installed it.
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