The inlet manifold is the cast iron passage that connects the carburettors to the cylinder head intake ports, and its bore size must match the carburettor specification fitted to the engine. There are two distinct inlet manifolds in the TD and TF range, and the mounting hardware between the carburettor and the manifold also differs between the standard TD and the Mark II and TF specifications.
Manifold Bore Sizes
The standard TD with its H2 carburettors of 1.25-inch bore uses an inlet manifold with matching 1.25-inch internal bore. The TD Mark II and all TF models with their H4 carburettors of 1.5-inch bore use a larger inlet manifold with 1.5-inch internal bore. The Mark II specification included a bigger intake manifold as standard, reflecting the increased air flow demanded by the larger carburettors and higher-compression engine. Fitting the wrong manifold size, particularly fitting a small-bore TD manifold with H4 carburettors, will create a restriction in the intake tract that defeats the purpose of the larger carburettors and limits engine output.
Manifold-to-Head Mounting
The inlet and exhaust manifolds share a common set of studs and clamps securing them to the cylinder head. Four studs thread into the head, with clamps and nuts that hold both manifolds simultaneously. The manifold gasket that seals between both manifolds and the head is a single shared gasket common across all TD and TF specifications. This shared gasket arrangement means that both manifolds must be removed to replace the gasket, even if only one manifold is being serviced.
Carburettor-to-Manifold Mounting
The mounting between the carburettors and the inlet manifold uses spacers and gaskets that differ between the standard TD and the Mark II and TF. The standard TD uses a specific spacer between each H2 carburettor and the manifold face, with its own gasket. The Mark II and TF use a different spacer for the H4 carburettor mounting, with the gasket quantity increasing from two to four on the TF installation. Carburettor-to-manifold bolts, studs, and spring washers complete the mounting arrangement.
The spacers serve as both a heat insulator, reducing heat transfer from the manifold to the carburettor body, which would cause fuel vaporisation and hot-start problems, and as an alignment interface between the carburettor flange and the manifold face. Damaged or compressed gaskets at this joint will cause air leaks that lean the mixture and create erratic idling that is difficult to diagnose without smoke-testing the manifold joints.
Ordering Considerations
The key identification for inlet manifold ordering is the carburettor bore size: 1.25-inch for standard TD, or 1.5-inch for Mark II and TF. The manifold-to-head studs, clamps, gasket, and nuts are universal across all variants. The carburettor-to-manifold spacers, gaskets, and hardware are specific to the carburettor type.