An ignition coil (1; 30) for triggering combustion in a controlled ignition endothermic engine displays: a magnetic circuit (2; 31) having a core (5; 32) and a cladding (6; 33); a primary electrical circuit (3) wound around the core (5; 32); a secondary electrical circuit (4) wound around the core (5; 32) and concatenated with the primary electrical circuit (3); at least one air gap (12; 39) defined by the magnetic circuit (2; 31); the magnetic circuit (2; 31) being formed by at least one first part and one second part (7, 8; 34, 35) capable of sliding one with respect to each other to adjust the dimensions of the air gap (12; 39).