The cylinder head has hemispherical combustion chambers (correct statement would have been "pear shaped chambers" since this has implications on the angle of the valves). Valve sizes are diameter inlet and diameter exhaust on all engines except the later "Big Valve" engines. The valve stem axis is inclined 27° from vertical on both intake and exhaust. Initial cam timing was 15/53/53/15 with the same cam profile as the ET418 Coventry Climax FWE cam, which resulted in at 5700 rpm for the 1.5-litre with a 9.5:1 compression ratio.