Air Pump

From Citroen SM Wiki

All US-spec cars have period typical additional combusting exhaust headers.

US-spec cars have "manifolds" that have inlets that are connected to a belt-driven air pump, also known as a smog pump.

See for details about the theory.

These could glow red-hot sometimes in normal operation which requires caution. If I understand correctly, the shields could become soaked with oil dripping from the valve covers and this could lead to "unintended external combustion". Drip trays which carry away any spilt oil were therefore fitted as standard, cliping to the rocker covers.

The pump can be removed quite easily and the inlets to the manifolds can be capped with a standard iron 1/2" threaded pipe cap.

If you remove the pump you will wish to consider rejetting the carburetors to Euro-spec. Use an emissions tested to verify CO. 2% is the specified maximum, and reportedly 1% is easily achievable.