When you search here for that very thing, many claim to offer "remove this" or Replace that - type of approach, but to be honest, look under there.
Starting with the Catalyst on towards the back - it's pretty much one piece and you have the Resonator (Collector) and then the Muffler - in two different sections of the car - one; the main muffler is at the back, while the Resonator (I call it a collector due to the nature of the device) acts as a means to take up the pulsing of exhaust from the single downpipe into and thru, past the catalyst - to help slow the flow of pulses and begin the smoothing effects (hence Resonator) towards the muffler.
Many just remove that resonator but fail to acheive the desired effects, for several reasons - so do some research first to save your money for your true effort at the "Moneyball".
So when you take out your calipers to measure diameters - are you looking at backflow / pressure problems or just generating a tuned effect?
Backpressure is a needed restriction for the system to even survive these days. The heat produced from the fuels used in todays cars is vastly different - so the burn rates - onto the ash particulate content is pre-set by the emissions - playing with this is literally playing with fire - heat is used to help the catalyst "modify" the exhaust - but too much of a good thing - usually is. You can form a small "Chernobyl" if you try to play with mixtures and even ream out or melt down it's core to reduce the backpressure needed to handle emissions- you're simply shortening the life of the vehicles ability to take you anywhere - what good is that?
- IF you're a parent - remember too you don't want to have the kids in the backseat getting "Gassed" while they are chauffeured by you - I can attest to the facts that the schools systems do notice your childs actions upon arrival to school - some lackadasical-attitude is fine and understandable - but acting close to comatose and smelling of the stench from the exhaust from a passing bus will raise eyebrows.
Best to leave the catalyst - even though it's what changes the whole mess...
Tuning exhaust - Then you're into a realm of music like that similar to Brass instruments - start with the tuba and then onto the trombone to develop the tone of the effects you want to have. Resonations can be both destructive and constructive - what Ford and others try to do, is considered destructive - Anti nodal - cancellation - so if you like the tone of "D" you might want to buy a vehicle with an engine that pushes more air out of the system to handle that note - the Fiesta - to me, is in the Key of "F". - No offense -
Sorry
Even V8 motors are hard pressed to push past the key of "D" even in the Treble cleft range - the Bass Cleft is still above that rumble (sub-bass BBB♯) but that is from the slower idle "push" or wellspring of emptying the cylinder does once the "puff" is exhumed from the stroke. It's hard to beat, (ahemn) that effect from the engine but remember too, the engines' 8 cylinders are firing at 90 degrees from each other, while a V6 has 120, onto the 4-cylinder using 180 degrees of rotation before the next puff, so you'll begin to see where the effort to acheive a particular sound does better when you have the instrument or engine design to produce the effect is already under the hood that pushes enough air into the system to acheive it.
So unless you like to listen to loose lugnuts and rivet rattle - trying to get more out of the system you currently have requires more than the space under the hood than what it currently can provide. However, you can "tune the system" with more of a pre-set length of tube to help the Bass notes and rumble effect you do have enough power in volume and air pressure to produce - versus making the thing sound like you just arrived on a Stihl 2-cycle Chain saw...
The above is a cutaway of a Ford Exhaust muffler for a F150.
- Ok, many would ask, "You know...that is not on the Fiesta..."
- No, it's not, but is to prove a point.
- Note the use of chambers and the main inlet tube is using two with each one a branch Tee - note the lengths of the Tee and the location of the main Port is one of the last before the final one that is the tailpipe - using the effects of wave cancellation because of the backpressure the system has in this area - slows down the puffs, this is pretty much the what Ford applies to all their Muffler systems.
- Also, they do not use Fiberglass - it just doesn't last as long or is as durable.
- Many feel the Exhaust system for the Fiesta seems to be it's biggest loss of power.
- In reality - it's not. Many other sites have proven that a small level of backpressure in the system helps with Low-End Torque. Like Here and even over here...
- An effect called "scavenging" can ruin the ability to use the leftover unburned exhaust fumes from the combustion to offer a bed of added fertilizer to make the next stroke more productive.
- Yes, I said that, because of an event with Valve timing and the slower release of the exhaust on low RPM moments. You can change the valve timing to allow the exhaust and intake to either overlap, or not - to allow the vacuum in the pipes and cylinder - to enhance the intake of fresh charge and to remove the exhaust - but utilize the vacuum present - to remove and displace - what is left in the cylinder.
- Ok, I remember a thread or maybe two about how motors evolved thru the years and now Sigma, Ford's latest, is a 4 port system - 2 intake - 2 exhaust, while other earlier versions used one intake (albeit very large port) and two exhaust.
So although it seems counterproductive, the tone of resonation can be located further back to the rear of the car using longer pipes of a progressive diameter to offset the loss the resonator - which counterproduced the effect of what you wanted - but then remember too, the predominate note the engine produces requires the engine to be far larger in output volume of air in a given pressure to obtain the lower notes - you can only get so much out of it.