Citroën produced the BX Sport from 1985 to 1987. During this period, Citroën manufactured 7,500 BX Sports; 2,500 in the first series, then an extra 5,000 due to its sales success. Rated at 126 PS (93 kW) at 5800 rpm and equipped with dual twin-barrel carburettors, the BX Sport was the most powerful BX in production at that time. The engine modifications, including a reshaped combustion chamber and larger valves, were developed by famous French tuner Danielson. It also stood out with its unique body kit, alloy wheels (later available on the GTi), a unique dashboard and Pullman interior. The body kit included a rear wing, side skirts, and fender extensions that added 10 cm to each side of the car, in order to accommodate the larger wheels. The car was only available in LHD, so it was not sold in the United Kingdom. Period road tests complimented the ride quality (as usual with Citroëns) but complained that the driving characteristics were not all that sporty as a result, even though the suspension had also been modified.
The BX GT was launched in 1985 and featured a 1.9 litre Peugeot-sourced engine, essentially the Sport engine with only one twin choke carburettor. Max power was 105 PS (77 kW). That same year, Citroën produced a “Digit” model, which was based on the BX GT. It featured a digital instrument cluster and an onboard computer. Citroën only produced 4,000 BX Digits in 1985.
Citroën entered Group B rallying with the BX in 1986. The specially designed rally BX 4TC bore little resemblance to the standard BX. It had a very long nose because the engine (a turbocharged version of Chrysler Europe’s Simca Type 180 engine) was mounted longitudinally unlike in the regular BX. The engine was downsleeved to 2,141.5 cc (from 2,155 cc) to stay under the three-litre limit after FIA’s multiplication factor of 1.4 was applied. The rally version of the BX also featured the unique hydropneumatic suspension, and the five-speed manual gearbox from Citroën SM. Because of the Group B regulations, 200 street versions of the 4TC also had to be built, with a 200 PS (147 kW) at 5,250 rpm version of the N9TE engine.
The 4TC was not successful in World Rally Championship competition, its best result being a sixth place in the 1986 Swedish Rally. The 4TC only participated in three rallies before the Group B class was banned in late 1986, following the death of Henri Toivonen in his Lancia Delta S4 at the Tour de Corse Rally. Already discouraged by the car’s poor performance in motorsport and the demise of Group B, Citroën was only able to sell 62 road-going 4TCs; build quality and reliability problems led Citroën to buy back many of these 4TCs for salvage and destruction. With only a fraction of the original 200 examples remaining, the 4TC is now highly sought-after.
An uprated version of the BX GT, the BX19 GTi was fitted with an 1.9 litre eight-valve fuel injected engine producing 122 PS (90 kW) (this engine also fitted to the Peugeot 405 SRi, and was very similar to the engine also fitted to the 205 GTi, however the BX19 GTi and Peugeot 405 SRi used a different inlet manifold and cylinder head), a spoiler and firmer suspension spheres/anti-roll bar than the standard model; it could reach 198 km/h. There was also a special export model, the BX16 GTi, using the 113 PS (83 kW) XU5JA engine from the Peugeot 205 GTi 1.6. Top speed was 194 km/h.
In May 1987, a 16 Valve version of the GTi was launched. This was the first mass-produced French car to be fitted with a 16-valve engine. A DOHC twin-exhaust port cylinder head, based on that of the Peugeot 205 Turbo 16 Group B rally car was bolted to an uprated version of the 1905cc XU9 8v alloy engine block as fitted to the BX GTi and Peugeot 205 GTi. The result was the XU9J4; a naturally aspirated 1.9 litre engine, (also fitted to the phase 1 Peugeot 405 Mi16) producing 160 bhp (120 kW) and 177 N·m (131 lb·ft) of torque. It produced a specific output of 84 bhp/litre, which for a fixed cam-timing, naturally aspirated engine was fairly impressive at the time. This helped rocket the BX to 100 km/h (62 mph) in 7.4 seconds and then 160 km/h (99 mph) in 19.9 seconds before finally reaching a top speed of 220 km/h (140 mph). Anti-lock brakes were fitted as standard. Its side skirts made it easily recognizable from all other BX models. In 1990, the facelift of the 16 Valve gave the car a new lease of life. The updated car came with new fibreglass bumpers, anthracite painted wheels, smoked taillight lenses, and a redesigned rear spoiler. These cosmetic changes made the car look even more distinctive from other BXs. There were also a few subtle changes made to the car’s performance, the most noticeable being harder suspension and a thicker anti-roll bar, which improved handling. The BX 16 Valve was faster around a race-track than the “in house” competitor Peugeot 405 Mi16.