The MGC exhaust manifold is a two-piece cast iron assembly comprising separate front and rear sections, each carrying three exhaust ports from the six-cylinder engine. The two-piece design was necessary to accommodate the length of the inline six-cylinder engine and the thermal expansion differences across the cylinder head. Both manifold sections bolt directly to the cylinder head using the fifteen studs shared with the inlet manifold, the same studs serve both manifolds simultaneously, which means removing or refitting either manifold requires the other to be at least loosened.
Manifold Specifications
The front and rear manifold sections for home market and most export cars differ from the USA and Canadian specification pair. The North American manifolds incorporate additional bosses and connections for the air injection emissions equipment that was mandated by federal regulations.
When ordering, specify the car's market to ensure the correct manifold pair is supplied. A manifold gasket seals the joint between the manifold faces and the cylinder head, this gasket should always be replaced during manifold removal, even if it appears undamaged, as heat cycling degrades the gasket material in ways that are not always visible.
Manifold-to-Front-Pipe Connection
Six studs, six spring washers, and six special nuts secure the manifold flanges to the front pipe assembly. Two manifold-to-front-pipe seals prevent exhaust gas leakage at this critical joint, a common source of 'blowing' that manifests as a rhythmic ticking noise from the engine bay, particularly noticeable at idle and low engine speeds. These seals should be replaced whenever the front pipe is disconnected.