Page 27 - Wayne Carini's Guide to Affordable Classics

THE BACKSTORY
A Heart Transplant
Enthusiasts often associate Big Healeys with throaty and torquey six-cylinder engines, and after the original model – the four- cylinder powered “100” – ended production in 1956, all of them had a big inline six under the hood. The first variant, christened the 100-Six (BN4), debuted in September 1956 and represented the evolutionary bridge between the iconic 100 and the more powerful 3000 that followed.
Austin-Healey 100-Six and 3000
BMC’s decision to standardize production around three main engine designs forced Donald Healey to abandon plans to adopt a detuned version of the 100S unit for standard production use and find a way to install the six-cylinder C-series engine into its small roadster. This should have been a positive development, especially since the 2639 cc unit was nominally more powerful than the existing A90 engine of similar capacity, but it also weighed much more, produced less torque and had a reputation for troublesome performance.
Moreover, the C-series engine did not seem well suited to powering a sports car, particularly since the cast iron cylinder head featured an integrated inlet manifold that compromised its ability to breathe and made it difficult to maintain a proper fuel to air mixture. With some effort, Morris Engines improved its refinement and increased the power output to 102 horsepower at 4,600 rpm and 142 lb ft of torque at 2,400 rpm, which was obtained with an 8:25:1 compression ratio and twin SU H4 carburetors.
In order to accommodate the length of the new engine, the radiator was moved ahead of the front crossmember, which required a longer forward-opening hood with a small intake to reduce temperatures under the hood. The same four-speed gearbox and hypoid bevel rear axle, fitted with different final drive ratios, used in the 100 BN2 were retained for use in the new car, but the clutch
TOP: Abingdon-built examples of the 100-Six, like the one seen here, were fitted with an improved version of the C-Series engine that could produce 117 horsepower at 4,750 rpm and 149 lb ft of torque at 3,000 rpm. Initial variants of the model were fitted with a less powerful engine that made 102 horsepower at 4,600 rpm and 142 lb ft of torque at 2,400 rpm. Both versions used SU H4 carburetors.
ABOVE: The first 100-Six variant to appear was the BN4 that introduced rear seats for occasional passengers. Although the front seats have leather faces, the rear cushions and back panel were covered in Vynide, which was also used to trim the fascia and top of the scuttle.
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