Dual-Stage TWC Catalytic Converters, Muffler & Tailpipe
Dual-branch Y-pipe, heated oxygen sensor, two-stage monolithic honeycombs, tri-flow muffler, and over-axle tailpipe.
Role in the System
What This Assembly Is
Sweeping down from the split exhaust manifolds along the passenger side of the ladder frame are the dual-branch Y-pipe, the Heated Exhaust Gas Oxygen (HEGO) sensor, the front and rear Three-Way Catalytic (TWC) converters, the aluminized steel tri-flow muffler, the over-axle tailpipe, and rubber isolator hangers.
Mechanics & Physics
How the Subcomponents Work Together
Three-Way Precious-Metal Catalysis: Inside the stainless converter shells sit ceramic honeycomb monoliths coated with a microscopic washcoat of platinum, palladium, and rhodium. As long as the HEGO sensor and EEC-IV computer oscillate the air-fuel ratio tightly around stoichiometry (14.7:1), rhodium strips oxygen atoms off NOx molecules (reducing them to N₂), while platinum and palladium use that freed oxygen to oxidize lethal carbon monoxide (CO) and unburned hydrocarbons into CO₂ and H₂O.
Other Assemblies in This System
Split Front (Cyl 1–3) & Rear (Cyl 4–6) Exhaust Manifolds
Two separate nodular-iron 3-into-1 exhaust manifolds that eliminate thermal warping and scavenge paired 240° firing pulses.
EGR Valve, EVP Position Sensor & Stainless Exhaust Tube
Meters inert exhaust gas back into the intake manifold under part-throttle cruise to suppress peak combustion temperatures and NOx.
Thermactor Air Pump, Diverter Valve, Check Valve & Rail
Belt-driven rotary-vane air pump and 6-branch cylinder-head manifold that inject fresh oxygen to light off the catalytic converters.