Exhaust Manifolds

From Citroen SM Wiki

There are two types of exhaust manifolds. European models have a two-part equal-length setup, and US-spec models have a plenum-style upper header that (with the Air Pump) supports post-cylinder combustion. Theoretically for smog reduction.

Euro Headers

The Euro headers are vastly preferred.

The upper and lower parts are joined by five M7 bolts. When rebuilding, drill them out and tap to accept M8 bolts and use stainless fasteners. You may have to enlarge the gaskets slightly when re-installing

Manual transmission cars have a standard exhaust-type gasket between the upper and lower parts. Automatiques have an extra spacer, which is about 1/4 inch thick (about the same thickness as the pads under the motor mounts) and therefore require two exhaust gaskets per side. (dimensions or photo needed?).

VW Bug exhaust gaskets are good replacements for the exhaust manifold gaskets.

US Manifolds

These get red-hot and have been implicated in fires when any fuel leaks.

If you remove the Air Pump you can cap the line to the manifold with a standard pipe cap.