The High-Output 307 available in the H/O and 442's use a Dual-Outlet exhaust system. Its components include the headpipe, which connects the catalytic converter to the back of the passenger side exhaust manifold, the intermediate "Y" pipe, two resonators, and two tailpipes.
The High-Output dual outlet exhaust system uses a pair of cast iron manifolds bolted to the heads. Tubular steel exhaust manifolds were used briefly on the roller lifter, 7A headed, 307 when it was first introduced. Exhaust gases from the driver side manifold are directed by an crossover pipe to the passenger side manifold. An exhaust pipe bolted to the passenger side manifold directs the exhaust gases to the catalytic converter mounted under the front passenger floorpan. The catalytic converter is of a dual-bed monolithic design. The first bed being a 3-way catalyst, reducing Carbon Monoxide (CO), Hydrocarbon (HC) and Nitrous Oxide (NOx) emissions, the second bed is a 2-way catalyst that futher reduces CO and HC emissions.
After the catalytic converter an intermediate "Y" pipe separates into two 2.25" pipes that each end at a resonator on either side of the propeller shaft, just ahead of the rear axle. From the outlet of each resonator a tailpipe travels up and over the rear axle and to each side of the vehicle just behind each rear tire where the exhaust gases are exited to the atmosphere.
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