A catalytic converter is neither a filter nor a silencer. Its internal substrate carries a washcoat loaded with precious metals, and those metals promote reactions that turn leftover hydrocarbons, carbon monoxide and oxides of nitrogen into less harmful compounds. Nothing is trapped and stored. The unit only works once the substrate is hot, so temperature is as much a design input as fitment.
That distinction matters when you are diagnosing rather than ordering. A converter contaminated by coolant, oil or an over-rich mixture can still flow freely and look intact from outside while converting very little. A restriction that shows up on a gauge is a different failure from a converter that has quietly gone chemically lazy.
Position decides how fast the substrate reaches working temperature. A close-coupled unit right after the manifold heats quickly but lives with the harshest heat and vibration in the system. A unit placed further back sees gentler conditions and takes longer to become effective, which is why many modern cars carry more than one.
Aftermarket routing frequently moves the converter because the pipe path changed or clearance demanded it. Treat that as an engineering change rather than a cosmetic one. Ask where the gas is when the engine is cold, and whether the sensor monitoring the converter still sees what the control strategy expects. Our exhaust pipe range is where that routing decision begins.
Aftermarket converters vary in three ways that matter: the substrate inside, the housing around it, and how the assembly is mounted. Two units that fit the same car can differ in all three, so compare internal construction rather than appearance.
The housing decides how the part takes heat cycling, and the mounting decides whether the converter is stressed or supported. A unit loaded by its own pipe will fail at the welds whatever the substrate is worth. That is a fabrication question, not a parts question.
The substrate is a honeycomb. A denser honeycomb packs more surface into the same volume, which helps conversion but also adds restriction and leaves the gas less room to pass. A more open honeycomb flows better and converts less effectively, especially when cold. Neither choice is automatically right; the balance follows the use case.
For a road car that must behave on cold starts, the denser side of the trade is usually the honest answer. For a competition car that is always hot under load, the open side is common because the converter exists to satisfy a class rule. Do not assume any aftermarket converter flows better simply because it is aftermarket.
Converters run hotter than the rest of the system and cycle between hot and cold repeatedly. That cycling is what breaks poor work. Welds that were sound when cold can crack as the assembly expands against its own restraint, and thin material near the inlet is usually where it shows first. Good fabrication, not a particular alloy, survives it.
Stainless steel is the ordinary choice for road systems because it tolerates heat cycling and everyday weather. Titanium is selected when saving weight matters more than cost, and it demands a clean, controlled weld because the material reacts badly to contamination at temperature. Both appear in our titanium exhaust system work, and both are judged the same way: does the joint survive the cycle?
Confirm the legal position first, because emissions rules differ by market and model year, and a modification that suits a track car may not be road legal where the vehicle is registered. Then confirm the practical items: sensor bosses in the right places, room for expansion, and a mounting arrangement that does not load the converter body.
Finally, decide what you actually want. If the goal is a compliant road car with a better sound and a lighter system, the converter stays and the effort goes into routing and materials. If the goal is a race car, the converter is a rule requirement and its restriction is a cost you accept. Clarity here prevents most of the arguments later.
