OE pattern exhaust systems replicate the original factory specification in material, pipe diameter and construction. They are supplied in mild steel, the material used at the factory from 1955 to 1962, and match the factory system in appearance, sound, and interface with the rest of the car. For any MGA being restored to concours standards, the OE pattern system is the correct specification; for owners less concerned with concours originality but wanting the factory exhaust note and appearance rather than the different sound and finish of a stainless-steel system, it remains the original-specification choice.
Pushrod OE pattern, 1500, 1600 and 1600 Mk II
The pushrod OE pattern system is the single-silencer specification fitted to all three pushrod variants from the factory: a single downpipe off the three-branch manifold flange, a front pipe running along the left-hand side of the chassis, a simple tubular silencer towards the rear with two mounting brackets, and a tail pipe exiting to the rear. The system specification is identical across all pushrod MGAs, with the single factory deviation being late 1600 Mk II cars exported to Switzerland from car/chassis 108405, which carried an additional silencer in the front pipe to comply with Swiss noise legislation. Reproduction OE pattern systems replicate the standard non-Swiss specification.
Twin Cam OE pattern
The Twin Cam OE pattern system reproduces the factory twin-manifold specification: two downpipes from the Twin Cam's two exhaust manifolds, merging into a single front pipe forward of the silencer, running back along the left-hand side of the chassis and out through a tail pipe to the rear. The Twin Cam silencer is similar in form to the pushrod item but of a slightly different factory type, with a larger pipe diameter matched to the twin-downpipe feed. The Twin Cam OE pattern system is specific to the Twin Cam engine, it is not interchangeable with the pushrod system in any respect.
Mild-steel construction and service life
Mild-steel exhaust systems corrode over time through a combination of external road-salt exposure and internal attack from the combustion by-products and condensation that collect inside the pipework. Service life depends strongly on usage pattern and storage conditions: a car used for longer runs where the system reaches full operating temperature consistently, and stored under cover in dry conditions, will see materially longer service life than a car used for frequent short journeys where the internal condensation never evaporates and sits in contact with the steel between uses. Cars laid up for extended storage periods benefit from a drive to operating temperature immediately before and after the storage period, to drive moisture out of the system.
Finish
Original MGA mild-steel exhausts were supplied with a matt finish consistent with factory exhaust practice of the period. Modern reproduction OE pattern systems are typically supplied with either a similar matt finish or a protective paint or zinc coating to extend shelf life and early service life before the factory appearance develops in use. The finish darkens and weathers quickly in service, so a freshly-painted reproduction will look close to a period system within a few thousand miles.
OE pattern and concours considerations
Reproduction OE pattern systems are made to match the factory specification, but minor variations in bracket position, section length, or flange detail can exist between reproduction manufacturers. Owners pursuing concours judging should confirm the specific pattern detail of any reproduction system against the original factory specification and, where possible, against a known-original car. For standard restoration and road-use replacement, these minor variations are not significant. Owners not concerned with concours standards but wanting a longer-service-life alternative should consider the stainless-steel option under Upgrades & Alternatives instead.
Ordering considerations
Ordering begins with pushrod or Twin Cam, the two systems share no components. The pushrod OE pattern system suits all 1500, 1600 and 1600 Mk II cars of all markets except the Swiss-market Mk II variant. The Twin Cam OE pattern system is specific to the Twin Cam. When renewing the system, the manifold-to-head gasket, downpipe flange gasket and silencer rubber mountings should also be renewed as part of the job, these are available as service items under Manifolds & Fixings and Exhaust Fixings & Mountings respectively.
Where exhaust clamps are not part of the supplied system, matching clamp hardware should be ordered alongside.