The MGB GT V8 ignition system comprises the coil, distributor (covered separately), HT (high-tension) leads from the distributor cap to each spark plug, the eight spark plugs themselves, and various heat shields and protection components. The system generates the high-voltage spark that ignites the air-fuel mixture in each cylinder at the correct moment in the engine cycle.
Ignition Coil
The ignition coil is a step-up transformer that converts the 12-volt primary current (switched by the contact points or electronic trigger) into the high-voltage HT spark. Coil specification matches the factory V8 ignition system, the coil's primary resistance is matched to the contact points and ballast resistor (if fitted) to give the correct primary current. Coil replacement is straightforward when failure occurs (typically signalled by complete loss of spark).
HT Leads
Eight HT leads connect the distributor cap to each spark plug. Original leads use copper-cored construction with appropriate insulation; modern silicone-jacketed leads with copper or carbon cores offer better heat resistance and longer service life. Leads age in service: insulation hardens and cracks, internal connections degrade. Visible cracks or arcing under load indicate immediate renewal.
Spark Plugs
The factory V8 specification spark plugs are matched to the engine's compression ratio and operating conditions. Plug heat range, electrode gap and thread reach are all critical, fitting incorrect plugs causes performance and reliability issues. Plugs should be inspected at routine intervals, with electrode condition giving useful diagnostic information about engine operation.
Plug Lead Heat Shields
Heat shields were added to the factory specification at production stages V8 1956 (September 1974, four middle plug leads) and V8 2266 (February 1975, two front plug leads), protecting these spark plug leads from heat radiated by the cast-iron exhaust manifolds below. Cars built before these chassis numbers can have the heat shields fitted retrospectively as good practice, the shields significantly extend HT lead service life and reduce the risk of heat-related ignition misfire.
MGOC Spares
MGOC Spares supplies ignition coils, HT leads, spark plugs, plug lead heat shields and all ignition service components for the MGB GT V8.