Another innovative feature of the IMA engine's aluminum VTEC-E cylinder head is its integrated exhaust manifold. The individual exhaust-manifold runners are part of the head casting, just like the exhaust ports. The shape and length of the manifold runners is optimized for efficient flow, and the system offers the advantages of faster heat transfer to the catalyst, for faster lightoff. Eliminating the need for a separate exhaust manifold also increases manufacturing efficiency, and offers greater compactness and lower engine weight. The IMA engine is the world's first production gasoline engine to use an integrated exhaust manifold.
Lean air-fuel ratios improve fuel economy and reduce hydrocarbon, carbon monoxide and oxides of nitrogen; however, conventional 3-way catalysts are not very effective in converting NO~ into normal nitrogen when excess oxygen is present. To keep NO2 emissions within ULEV levels, Honda engineers added a new, nitrogen-oxide-adsorptive catalytic converter. The catalyst uses a proprietary mixture of platinum and other metals to attract NOx molecules to its surface (adsorption) during lean-air fuel mixture combustion. Then, when the IMA engine is operating with a richer air-fuel ratio, the catalyst combines these NOx molecules with the hydrocarbons and CO present in the exhaust to form water vapor, carbon dioxide and nitrogen. The engine's nitrogen-oxide-adsorptive catalyst plays an important role in helping the Insight achieve ULEV emission standards.