The MGB exhaust system uses a dual cast iron manifold, with the exhaust from cylinders one and four feeding into a Y-shaped manifold leading to the front downpipe, and the siamesed exhaust port from cylinders two and three feeding a single pipe in the centre leading to the rear downpipe. The twin downpipes join ahead of a centre silencer, with a rear interpipe leading to the rear silencer and tailpipe, which exits on the left-hand side of the car. This fundamental layout remained unchanged across production from 1962 to 1980, though there are important differences in both the manifold and silencer types that affect parts selection.
Early 18G-series engines used a thick-flange exhaust manifold, secured to the cylinder head by two outer studs and four inner studs of differing lengths. From 1971 onwards, the 18V-series engines were fitted with a thin-flange manifold incorporating a hot-spot facility for the carburettors, and this type uses six identical studs. Ordering the correct manifold, and the correct stud set, depends on knowing which engine series is fitted to the car. 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, carried through to end of production. The rear silencer was always a cylindrical type. The tailpipe was originally cut at a 45-degree angle, but on later cars it curved downwards and was cut at a right angle.
Throughout production, improvements were made to increase durability and reduce noise, a twin perforated tube front silencer from July 1963, double end plate silencers from March 1966, 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. These differences mean that replacement systems are specified by chrome bumper or rubber bumper application, across OE, stainless, and performance ranges.
OE Exhaust Systems
One-piece mild steel systems are available for both chrome bumper and rubber bumper cars, and can also be purchased as individual components, downpipe, front interpipe, centre silencer, rear interpipe, and rear silencer. The improved Club exhaust is a heavier-gauge mild steel system suited to both bumper types with a 15-month guarantee. Mounting hardware includes exhaust-to-gearbox brackets, which differ between 3-synchro, 4-synchro chrome bumper, and 4-synchro rubber bumper applications, along with U-clamps, exhaust straps, saddle brackets, and rubber bobbins. The rear mounting method changed during chrome bumper production from a pinch clamp arrangement on cars to 1970 to a saddle mounting from 1970 onwards.
Stainless Steel Systems
Stainless steel systems are manufactured in 309 and 401 grade stainless steel with mirror finish silencers and a lifetime guarantee. Four system types are available in chrome and rubber bumper variants: standard, bomb box, Sports Free Flow with twin polished tailpipes, and slimline. Complete performance packs combining a gas-flowed stainless tubular manifold with a full system are available in standard box, bomb box, free flow, and big bore configurations. Individual stainless components are also available separately.
Exhaust Fitting Kits
Fitting kits provide all clamps, mountings, and fixings required for each system type. Kits are system-specific, covering standard dimension systems for chrome bumper pre-1970, chrome bumper 1970 to 1974, and rubber bumper, as well as dedicated kits for free flow, performance packs, Club specials, road race, and big bore packs.