The BT46 was designed to succeed the Brabham BT45, which had been hampered by the weight and size of the Alfa Romeo flat-12 engine. The engine had a capacity of 2995 cc with fuel injection and electronic ignition, a magnesium alloy block, and four gear-driven valves per cylinder. In Formula One form by 1978 it delivered approximately 520 bhp at 12,000 rpm — around 50 bhp more than the Cosworth DFV used by most competitors — but brought greater weight, increased fuel and oil consumption, and significant dimensional variation between units. The chassis was an aluminium alloy monocoque with a trapezoidal cross-section.
The original BT46 design used flat panel heat exchangers mounted flush to the bodywork in place of conventional radiators. Consultant engineer David Cox calculated that this provided only around 30 per cent of the required cooling surface area and contacted Brabham with his concerns. After testing confirmed serious overheating problems, the heat exchangers were replaced with nose-mounted radiators similar to those of the BT45, compromising aerodynamic efficiency and moving weight towards the front. The car also featured early carbon composite brakes adapted from the aircraft industry and inbuilt pneumatic jacks fed from an external compressed air supply for tyre changes during practice.
In 1978, Lotus had developed full venturi tunnels under the Lotus 79, creating ground effect that gave Mario Andretti and Ronnie Peterson a substantial advantage from their first appearance at Zolder. Murray recognised that the wide Alfa Romeo flat-12 engine was too wide to permit the venturi tunnels necessary for ground effect on the BT46. He requested that Alfa develop a narrower V12 for the 1979 season; in the meantime, he sought an alternative means of reducing pressure beneath the car.
The concept drew on two precedents. In 1970, the Chaparral 2J had used twin fans driven by a dedicated two-stroke engine to extract air from beneath its chassis in the Can-Am series, proving significantly faster than its rivals before being banned. The Tyrrell 008, designed by Maurice Philippe, had also fitted a small rear fan driven from the crankshaft, ostensibly to extract air from radiators mounted under the car. Testing showed this system was ineffective and was abandoned; however, Cox, who observed those tests, recognised its potential and informed Murray.
Cox produced the overall layout for the BT46B, arranging the fan so that its primary claimed function was cooling, in order to satisfy the regulations. Murray designed a drive system using a complex series of clutches running from the engine to a large single fan at the rear, anticipating problems from fan momentum during gear changes — though in practice the clutches were not needed, making the suction effect proportional to engine speed. Like the Lotus 79, the car used sliding skirts to seal the gap between the sides and the ground, preventing air from dissipating the low pressure zone beneath. The two modified chassis, BT46/4 and BT46/6, were designed and tested in secrecy.
The BT46B was prepared for the 1978 Swedish Grand Prix at Anderstorp for Niki Lauda and John Watson. When not in use, the fan was covered with a dustbin lid. When drivers blipped the throttle, the car visibly squatted on its suspension as downforce increased. Mario Andretti described the effect as "like a bloody great vacuum cleaner." Murray disputed this, arguing that the fan's exit speed of only 55 mph meant it could not throw stones backwards and that any stones would be directed sideways by the radial fan.
The legality of the cars was protested but they were permitted to race. Lauda and Watson qualified second and third behind championship leader Andretti. Watson spun off on lap 19. After Didier Pironi dropped oil on the track and the main front-runners retired, Lauda passed Andretti around the outside of a corner; Andretti subsequently dropped out with a broken valve. Lauda won by over half a minute from Riccardo Patrese in an Arrows.
Lauda found that accelerating around corners caused the car to grip as if on rails, but described the car as unpleasant to drive due to extreme lateral loads and its reliance on aerodynamic grip over driver skill. In his autobiography he noted that the physical effort required by such g-loading would become a defining problem of the ground effect era.
Rival teams were immediately alarmed; Lotus began designing a fan version of the 79. Bernie Ecclestone, who had been secretary of the Formula One Constructors' Association since 1972 and became its president during 1978, was concerned that the controversy could destabilise FOCA at a critical moment in his consolidation of control over the championship. According to Ecclestone's biographer Terry Lovell, the heads of rival FOCA teams led by Colin Chapman threatened to withdraw support for Ecclestone unless the BT46B was withdrawn. Ecclestone negotiated an arrangement within FOCA for the car to continue for three more races before voluntary withdrawal, but the Commission Sportive Internationale intervened to declare fan cars impermissible going forward. The car never raced again in Formula One.
The Swedish Grand Prix win stood, as the car had not been ruled illegal when it raced. The two modified chassis were converted back to standard BT46 configuration for the following race. Murray later stated that Ecclestone "was working on getting his foothold in the Formula One Constructors' Association and launching himself towards what he's doing now."
The standard BT46 continued through the season, with Lauda winning the Italian Grand Prix, albeit after Mario Andretti and Gilles Villeneuve were penalised a minute for jumping the restart following Ronnie Peterson's fatal accident at the first start. The BT46 made its final championship appearance at the first round of the 1979 season, where Nelson Piquet retired on the opening lap following a multi-car collision.
A BT46 ran in B specification one further time in 1979 at the Gunnar Nilsson Trophy at Donington Park, a non-FIA time trial event held to raise funds for the Gunnar Nilsson Cancer Fund. Piquet drove, finishing fourth of the five competing cars.
Murray had designed a follow-up called the BT47 for 1979 featuring twin variable-geometry fans at the rear to maximise ground effect in the Chaparral 2J manner. The car was never built after the FIA closed the regulatory loophole. A third variant, the BT46C, moved the radiators from the front wing to a position behind the front wheels, replacing them with units from a Volkswagen Golf. The BT46C ran only in practice for the 1978 Austrian Grand Prix; drivers complained of reduced revs and straight-line speed, and it did not appear again.
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.
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