The MGB exhaust system comprises a cast iron manifold with twin downpipes joining ahead of a centre silencer, a rear interpipe leading to the rear silencer, and a tailpipe exiting on the left-hand side of the car. This fundamental layout remained unchanged across production from 1962 to 1980, though the centre silencer, tailpipe profile, and manifold type all changed, differences that affect parts selection and compatibility. The centre silencer was originally a flattened oval section on chrome bumper cars.
From the start of rubber bumper production in 1974, this changed to a crimped box type, which was then carried through to end of production. The rear silencer was always a cylindrical type.
On chrome bumper cars the tailpipe was cut at a 45-degree angle with a straight exit, while on later rubber bumper models the tailpipe curved downwards and was cut off at a right angle. Throughout production, various improvements were made to the system to increase durability and reduce noise, including improved material specification in 1968, a stainless steel tailpipe from October 1969, and a three-pass front silencer from September 1977 to meet EEC noise regulations of a maximum 82dB.
Cast Iron Manifold
The original cast iron exhaust manifold was used throughout production, with two types fitted across the engine range. Early 18G-series engines (1962 to 1971) used a thick-flange manifold, while 18V-series engines from 1971 onwards were fitted with a thin-flange manifold incorporating a hot-spot facility for the carburettors. The exhaust manifold shares fixing studs with the inlet manifold, and the stud configuration differs between the two types, the thick-flange uses two outer studs and four inner studs of differing lengths, while the thin-flange uses six identical studs. Brass nuts are recommended for the manifold-to-head fixings.
Three-Branch Tubular Manifold
For owners seeking improved performance, a three-branch tubular manifold can be fitted in place of the cast iron unit. The individual primary pipes merge into a collector, promoting more efficient exhaust scavenging and smoother gas flow. The result is improved throttle response, a broader spread of torque, and a modest increase in power, particularly when combined with a Stage II cylinder head or performance camshaft. A tubular manifold will create a leaner combustion environment, so richer carburettor needles are recommended with the car set up on a rolling road after installation.
When fitting an aftermarket tubular manifold on cars with the 18V thin-flange inlet manifold, owners may encounter misalignment, repair washers cut in half on the inlet manifold side of the studs will take up the gap.
Replacement Exhaust Systems
Replacement systems are specified by chrome bumper or rubber bumper application, reflecting the centre silencer difference, across mild steel, stainless steel, and performance ranges. Systems are available in standard, bomb box, free flow, and slimline configurations, with performance packs combining a tubular manifold with a complete system. Low-profile centre box options are available for cars with lowered suspension. Exhaust fitting kits are tailored to specific model periods and matched to the system being fitted.
The front exhaust-to-gearbox bracket differs between 3-synchro, 4-synchro chrome bumper, and 4-synchro rubber bumper applications. The rear mounting method changed from a pinch clamp arrangement on cars up to 1970 to a saddle bracket from 1970 onwards. The MGOC Spares MGB exhaust range covers cast iron manifolds, tubular performance manifolds, complete exhaust systems in mild steel and stainless steel, individual system components, fitting kits, manifold gaskets, brass fixings, and all associated exhaust hardware.