The MGC uses oval air filter housings mounted on the carburettor intakes, each containing a replaceable paper filter element. Two elements are required per car, one for each SU HS6 carburettor. The air filter's role is to prevent dust, grit, and road debris from entering the carburettor and being drawn into the engine, where abrasive particles would cause accelerated wear to the cylinder bores, piston rings, and valve guides. A dirty or clogged filter element restricts airflow to the carburettor, enriching the mixture and reducing power, on the twin-carburettor MGC, if one filter is more restricted than the other, the two carburettors will receive different airflow volumes, causing an asymmetric mixture that produces rough running and uneven cylinder-to-cylinder fuelling.
Filter elements should be inspected at every service and replaced at least annually or every 6,000 miles in normal road use, more frequently if the car is driven on dusty or unsurfaced roads. The housings are secured by mounting plates, the front and rear carburettor mounting plates differ from one another, with bolts, nyloc nuts, and gaskets. Sealing washers in rubber and fibre ensure an airtight seal between the housing and the carburettor intake, preventing unfiltered air from bypassing the element. The front carburettor mounting plate changed at the 1969 model year (engine number 29G/3201), when it was commonised with the 29GA specification, the revised plate is identifiable by its different bolt hole pattern.
The number of air cleaner-to-carburettor bolts also differs between markets: four are required for standard UK-specification air filters, while USA and Canadian air filters use only two. This market difference must be observed when ordering mounting hardware.
Performance Air Filters
Three alternative air filter options are available for owners seeking improved airflow over the standard paper elements. Chrome-plated accessory-type foam filters provide a basic airflow improvement with a distinctive engine bay appearance. Chrome SU-style filters carrying the distinctive SU logo enhance the engine bay while providing genuine airflow improvement, and their more compact profile compared to the standard oval housing makes the carburettor tops more accessible for routine maintenance and tuning adjustments. K&N stainless steel pancake filters are the most efficient option, providing up to 40% more airflow than conventional paper elements with extremely high filtration levels.
K&N filters use an oiled cotton gauze medium that can be cleaned, re-oiled, and reused, reducing long-term costs compared to disposable paper elements. All performance filter options are supplied pre-fitted for immediate installation.
Stub Stacks
Stub stacks are short trumpet-shaped velocity stacks that fit between the carburettor intake and the air filter, smoothing the airflow entry into the carburettor choke and reducing the turbulence that occurs when air enters a flat-faced intake. The result is a measurable improvement in volumetric efficiency, more air enters the carburettor per intake stroke, which translates directly into improved throttle response in everyday driving. Stub stacks are highly recommended for use with either SU-style or K&N filters and represent one of the most cost-effective performance improvements available for the SU HS6 installation. They can be fitted in minutes and the improvement is immediately noticeable.