On early carbureted Volvos, the intake and exhaust manifolds are cast integrally. A preheating chamber is located within the combination manifold. The chamber's function is to transfer the heat from the exhaust ports to the fuel-air mixture in the intake manifold for improved cold weather operation. As the manufacturer moved to fuel injection for the U.S. cars in the early 1970s, the few remaining carbureted cars used separate intake and exhaust manifolds.
On all fuel injected and diesel Volvos, the intake manifold (inlet duct) and exhaust manifold are separate units. The inlet duct is constructed of a light aluminum alloy, while the exhaust manifold is cast iron.