The car grew out of Donald Healey's Nash-Healey two-door sports car, which used Nash mechanicals. Healey commissioned Tickford to build a single prototype — called the Healey Hundred — for the 1952 London Motor Show. The design caught the attention of Leonard Lord, managing director of Austin, who was seeking a replacement for the unsuccessful A90 Atlantic. Lord struck a deal with Healey to produce the car in quantity; the result was renamed the Austin-Healey 100.
Body styling was by Gerry Coker. The chassis was designed by Barry Bilbie with longitudinal members and cross-bracing for rigidity; the front bulkhead was welded to the frame for additional strength, and the rear axle was underslung to minimise overall vehicle height. Bodies produced by Jensen Motors in West Bromwich were mated with Austin mechanical components at Longbridge, a manufacturing arrangement previously used for the Austin A40 Sports. The first twenty cars were finished outside this arrangement; all subsequent production used the Longbridge line.
The first series, designated BN1, used the same undersquare 2660 cc four-cylinder engine as the standard A90 — 87.3 mm bore, 111.1 mm stroke, producing 90 bhp (67 kW) — paired with a three-speed manual transmission modified to include overdrive on second and top gears. Girling 11-inch drum brakes were fitted all round. Front suspension was independent double-wishbone with coil springs; the rear used a rigid axle with semi-elliptic leaf springs. Steering was by Austin's worm-and-peg system.
A BN1 tested by The Motor in 1953 achieved a top speed of 106 mph (171 km/h), accelerated from 0–60 mph in 11.2 seconds, and returned 22.5 mpg (imperial). The test car cost £1,063 including taxes. BN1 production ran from May 1953 to August 1955, with 10,030 units built. A 1954 BN1 (chassis #446766*4) is on permanent display in the Bonneville Salt Flats exhibit at the Simeone Foundation Automotive Museum in Philadelphia.
The BN2, introduced in August 1955, replaced the three-speed transmission with a genuine four-speed unit retaining overdrive on the top two gears. Other changes included slightly larger front wheel arches, a different rear axle, and the option of two-tone paint — the first Austin-Healey 100 to offer it. Colours available included Carmine Red (later replaced by Reno Red), Spruce Green, Healey Blue, Florida Green, Old English White, Black, and approximately 50 Gunmetal Grey examples. Two-tone combinations were White/Black, Reno Red/Black, Healey Blue/White, Black/Reno Red, and Florida Green/White.
By January 1956, production was running at 200 cars per month, with California alone accounting for 150 sales per month. The final BN2 was completed in July 1956; total BN2 production reached 4,604 units, including the 100M.
The high-performance 100M variant was introduced in 1955 with larger carburettors, a cold air box, a high-lift camshaft, and 8.1:1 compression pistons, raising output to 110 bhp (82 kW) at 4,500 rpm. Front suspension was stiffened and the bonnet gained louvres and a restraining belt. Approximately 70% of 100Ms were finished in two-tone paint; one was shown in White over Red and another in Black over Pink at the 1955 London Motor Show. The factory built 640 100Ms in total.
The same 100M components were also sold as the Le Mans Engine Modification Kit, installable in either a BN1 or BN2 with the engine in situ, raising power to approximately 100 bhp (75 kW) at 4,500 rpm. The kit was available to order from BMC, allowing private owners to self-modify. Factory-built 100Ms are distinguished from customer-converted cars only by their registered chassis identification numbers.
The 100S (for Sebring) was built primarily for racing and is the most specialised variant of the Austin-Healey 100. Its aluminium body contributed to an approximate 200 lb (91 kg) weight saving over the standard car. Output was 132 bhp (98 kW) at 4,700 rpm, achieved in part through a Weslake-designed aluminium cylinder head replacing the standard cast-iron unit; the overdrive was omitted. Dunlop disc brakes were fitted at all four corners, making the 100S the first production car in the world to feature disc brakes both front and rear.
Five works development and special test cars carrying "SPL" chassis numbers were built during 1953–1954; one of these won its class at Sebring in 1954, prompting the "S" designation. Only 50 production 100S cars were subsequently manufactured by the Donald Healey Motor Company at Warwick, hand-built and delivered between February and November 1955 under "AHS" chassis numbers. To reduce weight further, bumpers, the convertible hood, and a full-size windscreen were eliminated; the grille was reduced in size and the windscreen replaced with a plastic item. Most 100Ss were finished in two-tone white with Lobelia Blue sides; a handful were delivered in solid Spruce Green and red, with one in black.
An unrestored works 1953 100S special test car — campaigned by factory drivers Lance Macklin, Gordon Wilkins, and Marcel Becquart, and involved in the 1955 Le Mans disaster in which 84 people died and 120 were injured — sold for a world record £843,000 ($1,323,915) at Bonhams' December Sale on 1 December 2011.
Driver David Shale raced a 100S known as "EVV", achieving at least 13 podium finishes and four outright victories in the car. "EVV" sold for £673,500 at the Bonhams Goodwood Festival of Speed auction on 27 June 2014.
The BN1 and BN2 have competed successfully in vintage racing. In standard BN2 specification the car produces 90 bhp; in 100M specification it produces up to 110 bhp. With bumpers, interior trim, and carpets removed for weight reduction, and fitted with aluminium alloy wheels to accommodate wider, lower-profile tyres, significantly modified four-cylinder Austin-Healey 100s have competed against six-cylinder Aston Martins and twelve-cylinder Ferraris of the same era. BN-2 and 100M cars continue to appear at events such as the Pittsburgh Vintage Gran Prix.
The Austin-Healey 100 was the first of three models collectively known as the "Big Healeys", distinguishing them from the much smaller Austin-Healey Sprite. The successor Austin-Healey 3000 took its name from the near-3,000 cc displacement of its engine.
This article is based solely on the supplied corpus. No external sources were consulted; claims that could not be substantiated against the corpus were omitted under the drop-the-claim rule.