Loud pipes save lives.
Simple, elegant, timeless. Everyone reading this likes having a louder car. But what really goes into the cat-back or axle-back exhaust that you buy? How is the construction different? What’s the difference between a quality $800 exhaust and having Jim’s Muffler and Brakes weld something for you? For this Mud and Track Tech Tuesday, we’ll dive into the world of exhausts.
Let’s start simple, the (typical) universal layout of modern exhausts.
A) The exhaust manifold/header/collector bolts to the cylinder head. This is where all the waste gases from combustion in the engine first escape. As the exhaust valves open up, the gases head into the manifold.
B) The catalytic convertor. The major emissions component in the exhaust. The converter is typically filled with a honeycomb mesh of precious metals. These cause reactions in the exhaust stream to happen, removing unburnt hydrocarbons left over from combustion, converting them into carbon dioxide and water. After the 80’s additional materials were added to control emissions of nitric oxide and nitrogen dioxide.
C) The resonator is one of the first sound altering devices in the exhaust. It’s design is typically that of an enlarged tube, compared to the rest of the exhaust tubing. Their purpose, as the name implies, is to resonate the exhaust in an echo chamber of sorts, to adjust the tone of the exhaust. It quiets it somewhat, but primarily it is to adjust the tone by having the exhaust bounce off the walls before moving further downstream. Their design is such that they generally “cancel out” the drone-type noises that can come from exhausts. They also can reduce the pitch of the note to bring it down a bit, removing some of the rasp.
D) Finally, we have everyone’s favourite thing to cut off. The muffler! Again, the name is quite self-explanatory. It muffles the exhaust noise. Mufflers typically use a serious of chambers, or are filled with material like fiberglass, or both, to quiet the noise down. Mufflers can also have an effect on how the exhaust note sounds in terms of its tone. Mufflers can bring a note lower, and more of a rumble to the exhaust note.
All these different components ultimately have an effect on exhaust note tone and volume. In turbocharged applications, the turbocharger also effects the sound. When it comes to modifying your exhaust, the vast majority of people will go with either a cat-back or axle-back exhaust set up. A cat-back will typically run from the flange after the convertor and will include a new (or no) resonator and then get finished off with new muffler and tips. Axle-backs generally are bolt/clamp-on new mufflers and tips. A new manifold, or headers, are a popular choice amongst the V8 crowd. Larger diameter pipes, modifying the length of each pipe individually to perfect flow, there are lots of gains to be head with new headers.
While we don’t offer them, one of the other things you do see are replacements for the convertor. So called “race-cats” are marketed as being less efficient, freer flowing, but still attempt to reduce emissions. So, there is some performance gain to be had, while still maintaining legality (depending on jurisdiction.) There are also “test-pipes” or cat-less down pipes. These are only for race applications as they delete a mandated emissions device. I don’t think anyone would run these on the road, ever...wink. These generally off the biggest performance gain, at the expense of running afoul of local laws and typically come with a significant volume increase and generally finding your car smelling like a gas station fire.
We sell both cat-backs and axle-backs, both have their own positives and negatives. Axle-backs are generally less expensive, and typically result only in more volume, but not a massive change in tone. Cat-backs typically have a different tone from stock, and generally have a good bit more volume, they also tend to be a fair bit lighter than the stock exhaust components that they replace. And the easiest way to make a car faster is to shed weight!
When it comes to the creation of an exhaust, not all things are created equally. Generally, exhausts are manufactured from either T304 or T409 stainless steel. The quality of the stainless is important, because the high heat and prolonged exposure to sub-par road conditions is a breeding ground for rot and corrosion. T304 has better corrosion resistance than T409, but both have similar strength profiles and are worlds better than mild steel for corrosion resistance. It’s not just the material, but how it’s formed as well. The better exhausts are all mandrel-bent. This process has (typically) steel rod inserted into the pipe while it’s being bent to prevent wrinkling and crimping. When you have many thousands of dollars burning a hole in your pocket, you can also find welded pie-cuts for bends in your exhaust. It’s exceptionally expensive, and stunning fabrication work.
Engineered exhausts differ a fair bit from simply cutting out and replacing with a straight piece of pipe. A significant amount of research and design goes into optimizing the exhaust flow as well as producing a better or louder exhaust note in these systems. Similar to how your OEM system is designed to be the best possible compromise between efficiency, performance, sound, and cost. The muffler, converter, and resonator, all flow at a specific rate which is designed for the vehicles intended powerband. Making changes can affect the flow rate, which changes how the exhaust system scavenges spent gas from combustion. Usually, this results in an overall power gain of a few HP, but it does so at the cost of changing the power curve. You can end up losing low end performance in favour of a lot of noise and a tiny bit of power at the top end. That's why it's typically advised to go with something that has been clearly designed for your vehicle.
The ROUSH exhausts that we sell are all mandrel bent, and include both T304 and T409 stainless steel in their construction. Making them both cost-effective and improvements in performance. For most people, the two biggest considerations when choosing an exhaust are the sound, and the longevity. ROUSH covers both of those and generally comes with a performance boost as well.
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We have ROUSH exhausts for many Ford vehicles readily available, and as always, Mud And Track never charges duty fees or brokerage fees!