Fiesta st Catback exhaust nobody is talking about.

[Dialcaliper]

Mostly overall dB levels inside the car - Idle, and Cruise (65 and 80, or equivalent RPM (2700-3400) wherever it’s loudest. Unless they’re posted somewhere else.

With frequencies would be nice but not essential, especially wherever the 107-109 Hz shows up. The app I used is free, there are others out there as well.

 

[Clint Beastwood]

Many moons ago, in the UK, one of my uncles would soak his whole system in oil/paint mixture before he put it on his car. It would get burned off but he swore that his system lasted longer than normal.

I'll bet that smelled great

 

[Clint Beastwood]

Mostly overall dB levels inside the car - Idle, and Cruise (65 and 80, or equivalent RPM (2700-3400) wherever it’s loudest. Unless they’re posted somewhere else.

With frequencies would be nice but not essential, especially wherever the 107-109 Hz shows up. The app I used is free, there are others out there as well.

If you're using a phone for the measurements, they all tend to read a little high. The worst peak in the FiST should be about 106.67hz from instrumented testing.

 

[Dialcaliper]

^^^ They supposedly, somehow (without using a 20" foot long resonator, as some have suggested is necessary) got the 'bad drone frequencies' out by using a 'correct' Helmholtz device inside of the back box.

Just checked some numbers, and 109 Hz where I’m seeing a peak works out to exactly 3270 RPM, so the math checks out. I will note that the actual measurement the frequency bounces around a little bit between 107-109. It might also be due to very slightly higher exhaust pressure in a 2.5” system than a 3” system. And of course a smartphone is not exactly a precision measurement instrument.

A 109 Hz wave pulse length is ~3.15m peak to peak (it’s just speed of sound for 1/109th of a second). That’s ~124” which is plausibly in the right ballpark for the total length of the exhaust from exhaust valve to tip of tailpipe, which is generally the source of the droning frequency. There should be a harmonic at 2x that frequency as well, but that’s in the high RPM range where we expect loudness.

A quarter wave side branch resonator for that frequency then needs to be 1/4 of that - about 0.79m or ~31” long, which might be doable inside that offset rear muffler on the Thermal - basically a pipe running parallel to the main one inside the muffler with packing around both and connected at one end. That’s assuming that muffler is actually that long.

Always say “about” because that’s based on standard temp (20C) and atmospheric pressure - inside an exhaust is hotter and higher pressure which changes it a tiny bit (usually slightly longer)

 

[Clint Beastwood]

Yeah, there's a thread where I fixed drone on an MBRP system using a side branch. It was a neat coil of pipe where the muffler goes.

 

[Dialcaliper]

Yeah, there's a thread where I fixed drone on an MBRP system using a side branch. It was a neat coil of pipe where the muffler goes.

Is this the thread you’re talking about?

https://www.fiestastforum.com/threads/im-at-it-again-fixing-drone-on-a-brand-new-mbrp.20873/

I guess I’m late to the party - it’s good to see a firsthand case of a designed quarter wave that uses a curved (trombone style) pipe with multiple turns, and still works as designed. Definitely makes packaging it a lot easier!

One thing to mention - there’s a common misconception that people use quarter wave resonators just because full/half are too long, but that’s not the case. A full or half length side branch will actually amplify noise, and the quarter length is the correct design.

You want the pressure wave to enter the pipe and travel down it, and you want the side branch entrance to be at the lowest pressure point to cancel the main exhaust pulse and vice versa the now lower pressure zone shifts up the side branch as the main exhaust pressurizes and by the time it returns, it cancels the main exhaust high pressure pulse.

In the half wave case, the down and back will peak at the same time as the main pipe and amplify it. The full wave will amplify every other pulse. Quarter wave is where it’s at.

 

[Jcherry41290]

So I installed the flowmaster American thunder setup… I’m pleased to say that coming from a muffler delete, and an aftermarket resonator of which I don’t know the maker… the system sounds fantastic. Drone almost nonexistent. Which is a big difference from before, Around 2700 it would hammer in and vibrate parts in the interior and your inner ear lol. The fitment was great. The interior sound volume was so low that I was worried until I rolled the windows down, but thank god it has a great rasp and exterior sound quality is amazing. Pops and rumbles… sounds very similar to an abarth. Just like flowmasters promotional video claimed "they managed to maximize exterior sound quality while maintaining a mild interior volume." I think they nailed it. Drone was almost nonexistent. Has an almost hollow raspy sound it’s very pleasant!

 

[M-Sport fan]

As long as YOU like it (and it does not damage your hearing), is ALL that matters.

 

[Jcherry41290]

As long as YOU like it (and it does not damage your hearing), is ALL that matters.

Ha absolutely! I was interested in the thermal R&D also… guess I’ll just have to get another fiesta 😂 (I wish)
Cracking little cars… I think it will go down as one of the greats.. I almost wonder if ford engineers surprised themselves, like did they really anticipate that little platform to be as capable as it turned out to be lol

 

[Clint Beastwood]

Is this the thread you’re talking about?

https://www.fiestastforum.com/threads/im-at-it-again-fixing-drone-on-a-brand-new-mbrp.20873/

I guess I’m late to the party - it’s good to see a firsthand case of a designed quarter wave that uses a curved (trombone style) pipe with multiple turns, and still works as designed. Definitely makes packaging it a lot easier!

One thing to mention - there’s a common misconception that people use quarter wave resonators just because full/half are too long, but that’s not the case. A full or half length side branch will actually amplify noise, and the quarter length is the correct design.

You want the pressure wave to enter the pipe and travel down it, and you want the side branch entrance to be at the lowest pressure point to cancel the main exhaust pulse and vice versa the now lower pressure zone shifts up the side branch as the main exhaust pressurizes and by the time it returns, it cancels the main exhaust high pressure pulse.

In the half wave case, the down and back will peak at the same time as the main pipe and amplify it. The full wave will amplify every other pulse. Quarter wave is where it’s at.

Is this the thread you’re talking about?

https://www.fiestastforum.com/threads/im-at-it-again-fixing-drone-on-a-brand-new-mbrp.20873/

I guess I’m late to the party - it’s good to see a firsthand case of a designed quarter wave that uses a curved (trombone style) pipe with multiple turns, and still works as designed. Definitely makes packaging it a lot easier!

One thing to mention - there’s a common misconception that people use quarter wave resonators just because full/half are too long, but that’s not the case. A full or half length side branch will actually amplify noise, and the quarter length is the correct design.

You want the pressure wave to enter the pipe and travel down it, and you want the side branch entrance to be at the lowest pressure point to cancel the main exhaust pulse and vice versa the now lower pressure zone shifts up the side branch as the main exhaust pressurizes and by the time it returns, it cancels the main exhaust high pressure pulse.

In the half wave case, the down and back will peak at the same time as the main pipe and amplify it. The full wave will amplify every other pulse. Quarter wave is where it’s at.

Yeah that's one of them - I built a total of 2 full systems as well as messing with an mbrp because it was fun. If I had steadier I would build a complete system out of quarter wave resonators for every frequency that annoys me and have the chambers all lined up like a church pipe organ

I still need to build a system with a couple of helmholtz resonators to compare to the super-targeted quarter wave one. The quarter wave resonator on the mbrp was significantly less effective when the outside temp exceeded 100f, it was weird how noticeable it was.

 

[Clint Beastwood]

So I installed the flowmaster American thunder setup… I’m pleased to say that coming from a muffler delete, and an aftermarket resonator of which I don’t know the maker… the system sounds fantastic. Drone almost nonexistent. Which is a big difference from before, Around 2700 it would hammer in and vibrate parts in the interior and your inner ear lol. The fitment was great. The interior sound volume was so low that I was worried until I rolled the windows down, but thank god it has a great rasp and exterior sound quality is amazing. Pops and rumbles… sounds very similar to an abarth. Just like flowmasters promotional video claimed "they managed to maximize exterior sound quality while maintaining a mild interior volume." I think they nailed it. Drone was almost nonexistent. Has an almost hollow raspy sound it’s very pleasant!

If you could grab some sound bites that would be handy, like have a passenger hold a phone if you don't have a gopro or something, try to get some interior sounds going from a dead stop to "at speed". Would like to see the audio waveform to see how effectively they knock out the 106.67hz annoy-a-tone

 

[Mycooking]

I've been very biased towards the Borla systems but dang that price lol. Wife's R53 Mini has a Borla exhaust system and I love the sound coupled with that super charger whine and have a local FiST owner with the same system on his ST and aside from some drone at around 60 mph on both cars they hold up well in the salty New England winters. I also love the sound of the Flow master too. So many choices to make when my factory exhaust rusts apart.

 

[Business6]

I have had this exhaust for a couple of years now and love it. I've been wearing Loop earplugs for the last 8+ months which has helped tremendously as 24 of my 25 mile drive to work is on the highway and I was dealing with fatigue/irritability after as little as 20-30 minutes of driving.

It's definitely rusting up more than I want but I think it's the best sounding catback I've heard on this car. Cobb/FSwerks/Thermal will go on when it finally rusts through (two more years at most) but I'll need to hear the Thermal in person again as it didn't leave much of an impression.