Two more cylinders, two more inches of wheelbase — and the last big Healey without disc brakes.
August 1956. The four gave way to the 2,639cc BMC C-series six, the wheelbase went up two inches, the body grew about six and a half inches overall, a chrome-trimmed scoop appeared on the bonnet and the 100’s folding windscreen was replaced by a fixed one. The BN4 is the 2+2 with two occasional rear seats; the BN6, from late 1957, is a pure two-seater. Both ran to June 1959. The first cars had a small-port head and 102bhp on twin SU H4 1.5in carburettors; from late 1957 a high-compression six-port head and new inlet manifold took it to 117bhp on twin SU HD6 1.75in, and every BN6 is a six-port car. Production moved from Longbridge to the MG plant at Abingdon in the same period.
The 100-Six has drum brakes front and rear. All of them, always. This is worth stating plainly because at least one widely-read reference claims front discs on the BN4, and it is wrong — a restorer ordering front disc parts against a 100-Six would get something that cannot be fitted. Discs arrive with the 3000 in July 1959 and not before. Otherwise the car is the 100 stretched: same Jensen body pressings in principle, same independent wishbone and coil front, same live axle on semi-elliptic leaves, four-speed with optional overdrive. Because the C-series six carries straight over into the 3000, a good deal of engine, cooling and ignition stock suits both.
Austin Healey 100/6 — specification & changes within the model
- BN4
- August 1956 – June 1959. 2+2, with two occasional rear seats, later optional.
- BN6
- Late 1957 – June 1959. Two-seater. Every BN6 has the six-port head.
- Engine
- 2,639cc BMC C-series overhead-valve six, four main bearings. First series 102bhp @ 4600rpm, twin SU H4 1.5in sidedraught, small-port head.
- The six-port change
-
From late 1957 (production standard around October): high-compression six-port head and new inlet manifold, 117bhp @ 4750rpm, twin SU HD6 1.75in.
- Brakes
-
Drums front and rear, on every 100-Six. No 100-Six has front discs — a common and expensive error. Discs arrive with the 3000, July 1959.
- Gearbox
- Four-speed, overdrive optional.
- Body vs the 100
- Wheelbase up 2in; about 6.5in longer overall; chrome-trimmed bonnet air scoop added; the windscreen becomes fixed — the 100’s folding screen is gone.
- Built where
- Longbridge, then Abingdon from late 1957. Bodies by Jensen Motors.
- Parts overlap
- The C-series six carries into the 3000, so engine, cooling and ignition parts frequently suit both. Body, brakes and trim do not cross from the four-cylinder 100.
- Production
- Around 14,436 across BN4 and BN6 — sources differ, and the club figure is materially lower, so treat any total as approximate.
