In August of 1956, the big-Healey entered regular production with a six-cylinder engine and included a pair of small occasional seats in the rear. Met with considerable criticism, it replaced the more powerful four-cylinder unit and was a heavier car.

Chassis prefix for the first cars were introduced as BN4 which denoted a 4-seat roadster. Later in production a BN6 variant of the 100-6 was introduced in March 1958 as a 2-seat roadster. This was more inline with the original 100-4’s concept and it outsold the BN4.

In 1957 a new cast-aluminum 6-port intake manifold was introduced to the model that replaced the integral head unit. With larger valves, and a higher compression power was raised from 101 to 117 bhp. It also increased the price from £762 to £817.

Roy Salvadori said “the new 6-port induction system gives her an impressive increase in punch, particularly in top from 50 to 80 mph….the Austin-Healey always had plenty of dig but now its outstanding…”

The first sixes were built at Austin’s facility at Longbridge until December 1957 when production resumed at Abington. The model was discontinued in Match of 1959, but some BN7 models, better known as the 3000 MKI, were produced with 100-6 badges.

Donald Healey was an avid racing enthusiast so the six-cylinder Healeys were almost immediately on the track. Three modified cars were entered for the 1957 12-Hours of Sebring with streamlined bodies and Weber carburetors. One of the cars finished second in class. Another attempt was made at the same race with disc-brake cars. That same year Corvette racer Dick Thompson agreed to race a 100-6 for the 1958 SCCA Championship which he won.

BMC’s Competition Department prepared UOC741 (BN4) TON792, PMO201, PMO202 and PMO203 for rally at events such as Liège-Rome-Liège, the Coupe des Alps and the Tulip Rally. They never won outright, but the results were always first or second in class.