Marine exhaust manifold and header pipe system

An exhaust manifold for a multi-cylinder internal combustion engine comprising a manifold body configured internally thereof to define a plurality of inlet ports communicating within the body to an outlet port, the inlet ports opening through at least one engine face of the body via which the body can be mounted to an internal combustion engine of selected design for mating of the body inlet ports with respective exhaust openings defined by the engine in association with respective combustion chambers within the engine which fire in selected sequence, the outlet port opening from the manifold body through a second face of the body via which the body can be connected to an exhaust pipe assembly for conducting engine exhaust gases from within the manifold to a desired discharge location spaced from the body, septum means in the body having an end in the outlet port essentially at the second face for dividing the inlet ports into groups of at least two ports each and for isolating the body internal spaces associated with each group from the spaces associated with each other group, an exhaust pipe assembly connectible at an inlet end thereof to the manifold at the second face thereof, the pipe assembly including a duct defining a gas flow passage extending from the assembly inlet end and having an inlet opening matable with the manifold outlet port, and septum means in the duct and extending therealong from the passage inlet opening for dividing the passage into as many parallel parts as there are groups of manifold inlet ports, the pipe assembly septum means being disposed for substantial mating cooperation with the manifold septum means at the manifold outlet port upon connection of the pipe assembly to the manifold, the septum means being carried within the manifold and the pipe assembly in manners which accommodate differential thermal expansion and contraction of the respective septum means relative to the manifold body and to the duct.