BT49B
A BT49B specification appeared early in the 1980 season; it was conceived around a new transverse gearbox designed by American gearbox specialist Pete Weismann.
The new unit could be fitted with five or six gears and was tall and narrow, allowing a clearer airflow from under the car to the rear, with the intent of improving the ground effect.
An alternative rear suspension layout was designed to go with this gearbox.
It replaced the standard pullrods with rocker arms that activated vertical coil springs mounted behind the gearbox.
The Weismann unit proved difficult to make reliable and was used alongside the original gearbox, mainly on a spare chassis, until the Dutch Grand Prix, after which it was put to one side.

BT49T
A modified BT49, dubbed BT49T, was used to test the earliest versions of BMW's turbocharged Formula One engine between the 1980 and 1981 Formula One seasons.
This was a 1,499 cc (92 cu in) inline four-cylinder engine, with a single KKK turbocharger mounted in the left hand sidepod of the car.
The first version of the engine was said to produce 557 bhp (415 kW).

BT49C
For the 1981 season, a BT49C specification was produced with a chassis lightened through increased use of carbon composite materials.
Five of this variant were built and two of the previous year's cars converted to this specification.
That year a minimum ride height of 60 millimetres (2.4 in) was introduced and sliding skirts were banned, with the intention of limiting ground effect and slowing the cars.
The BT49C regained its front wings to compensate in part for the downforce lost.
More significantly, Murray devised a hydropneumatic suspension system for the BT49C in which soft air springs supported the car at the regulation height for checks while stationary.
At speed, where the ride height could not be measured, downforce compressed the air and the car settled to a much lower height, creating more downforce.
Because the skirts now had to be fixed, the suspension had to be very stiff to allow them to consistently seal around the sides of the car: by the end of the 1981 season, total suspension movement was only 1.5 inches (38 mm), half of which came from the compression of the tyres.
A lightweight qualifying chassis was produced, featuring a small fuel tank and lighter reinforced carbon-carbon brake discs and pads.

BT49D
Three new BT49D chassis were built for the 1982 season, featuring a still lighter chassis and one-piece bodywork.
By this stage, the cars had to be ballasted to bring them up to the minimum weight limit of 580 kg (1,279 lb) specified in the rules.
The BT49D used the carbon-carbon brakes as standard and was one of several DFV-powered cars to be fitted with large water tanks, ostensibly for "water-cooled brakes".
In practice, the water was dumped early in the race, allowing the cars to race as much as 50 kg (110 lb) under the weight limit; the regulations stated coolant could be topped up at the end of the race before the weight was checked.
In the view of the DFV teams, this practice met the letter of the regulations and equalised their performance with that of the more powerful turbocharged cars.
The 60 mm ground clearance rule was removed for the 1982 season, but the fixed skirts and very stiff suspension remained.
BT49B
A BT49B specification appeared early in the 1980 season; it was conceived around a new transverse gearbox designed by American gearbox specialist Pete Weismann. The new unit could be fitted with five or six gears and was tall and narrow, allowing a clearer airflow from under the car to the rear, with the intent of improving the ground effect. An alternative rear suspension layout was designed to go with this gearbox. It replaced the standard pullrods with rocker arms that activated vertical coil springs mounted behind the gearbox. The Weismann unit proved difficult to make reliable and was used alongside the original gearbox, mainly on a spare chassis, until the Dutch Grand Prix, after which it was put to one side.
BT49T
A modified BT49, dubbed BT49T, was used to test the earliest versions of BMW's turbocharged Formula One engine between the 1980 and 1981 Formula One seasons. This was a 1,499 cc (92 cu in) inline four-cylinder engine, with a single KKK turbocharger mounted in the left hand sidepod of the car. The first version of the engine was said to produce 557 bhp (415 kW).
BT49C
For the 1981 season, a BT49C specification was produced with a chassis lightened through increased use of carbon composite materials. Five of this variant were built and two of the previous year's cars converted to this specification. That year a minimum ride height of 60 millimetres (2.4 in) was introduced and sliding skirts were banned, with the intention of limiting ground effect and slowing the cars. The BT49C regained its front wings to compensate in part for the downforce lost. More significantly, Murray devised a hydropneumatic suspension system for the BT49C in which soft air springs supported the car at the regulation height for checks while stationary. At speed, where the ride height could not be measured, downforce compressed the air and the car settled to a much lower height, creating more downforce. Because the skirts now had to be fixed, the suspension had to be very stiff to allow them to consistently seal around the sides of the car: by the end of the 1981 season, total suspension movement was only 1.5 inches (38 mm), half of which came from the compression of the tyres. A lightweight qualifying chassis was produced, featuring a small fuel tank and lighter reinforced carbon-carbon brake discs and pads.
BT49D
Three new BT49D chassis were built for the 1982 season, featuring a still lighter chassis and one-piece bodywork. By this stage, the cars had to be ballasted to bring them up to the minimum weight limit of 580 kg (1,279 lb) specified in the rules. The BT49D used the carbon-carbon brakes as standard and was one of several DFV-powered cars to be fitted with large water tanks, ostensibly for "water-cooled brakes". In practice, the water was dumped early in the race, allowing the cars to race as much as 50 kg (110 lb) under the weight limit; the regulations stated coolant could be topped up at the end of the race before the weight was checked. In the view of the DFV teams, this practice met the letter of the regulations and equalised their performance with that of the more powerful turbocharged cars. The 60 mm ground clearance rule was removed for the 1982 season, but the fixed skirts and very stiff suspension remained.
Brabham BT49