Abstract: A swirl chamber and spark plug assembly comprises a unitary generally cup-shaped cylindrical member having external threads for removably installing it in the spark plug receiving hole of an internal combustion engine and a reduced diameter lower portion at the opposite end. The interior of the swirl chamber member has a central bore with internal threads at the top end and a stepped cylindrical swirl chamber defined by a lower cylindrical chamber and an upper cylindrical chamber of larger diameter for swirling gas in relation thereto. A spark plug having elongated electrodes is threadedly received in the top end of the swirl chamber with the spark plug gap at the juncture between the upper and lower chambers.