The Delta HF 4WD emerged at a pivotal moment in motorsport history. Group B rallying was terminated at the end of the 1986 season following a series of fatal accidents, and the new Group A regulations required manufacturers to homologate production-based cars built in quantities of at least 5,000 units within twelve months. Lancia had developed the Delta S4 as its Group B weapon, but the Delta HF 4WD had not been conceived as a rally car; it was a road car that proved suitable for conversion.
The four-wheel-drive system on the HF 4WD was derived from the system developed for the Delta S4, adapted from a longitudinal mid-engine layout to a transverse front-engine arrangement. Three differentials were used: an epicyclic centre differential controlled by a Ferguson viscous coupling split torque in a 56/44 front-to-rear ratio under normal conditions; a conventional open differential at the front; and a Torsen torque-sensing differential at the rear capable of locking up to 70 percent. The viscous coupling transferred torque from the faster-rotating axle to the slower one, maximizing grip under acceleration, and locked completely under extreme slip conditions.
The road car's 1,995 cc twin-cam eight-valve engine was derived from the Lancia Thema saloon. Equipped with a Garrett turbocharger, wastegate valve, air-to-air intercooler, and Weber IAW integrated electronic fuel injection and ignition, it produced 165 PS at 5,250 rpm and 260 Nm of torque at 2,750 rpm, with an overboost function allowing short bursts of up to 284 Nm. Suspension was MacPherson strut at all four corners, with power-assisted rack-and-pinion steering. Brakes were ventilated discs at the front and solid discs at the rear — standard across the sporting Delta variants.
Visually, the HF 4WD introduced the quadruple round headlights and new wraparound bumpers that the entire Delta range adopted with its 1986 facelift. Red piping around the grille, twin exhaust outlets, and HF 4WD badging on grille, skirts, and rear panel distinguished the top model from lesser variants. Inside, seats and door panels were upholstered in a combination of grey Alcantara and Missoni wool cloth; instruments featured yellow scales and hands.
The Group A Delta HF 4WD made its competition debut at the 1987 Monte Carlo Rally, taking first and second place in its opening round. From there it won nine of the thirteen championship rounds in 1987, claiming the Manufacturers' Championship for Lancia. Juha Kankkunen also took the 1987 Drivers' Championship at the wheel of a Delta HF 4WD.
The car also won the opening two rounds of the 1988 season before being replaced by the more developed Delta HF Integrale, which offered wider bodywork, uprated brakes, and a more powerful engine version to counter the increasingly competitive challenge from Ford, Toyota, and Mazda.
The Delta HF 4WD proved that a Group A road car, not purpose-built as a rally machine, could be transformed into a championship winner if the underlying engineering was sound. The three-differential four-wheel-drive system it introduced went on to power Lancia through six consecutive World Rally Championship titles between 1987 and 1992 — an unbroken run that remains a record. The car's commercial impact was notable: Lancia reported a 42 percent increase in Delta sales in the Italian market in the first half of 1987, directly attributed to the HF 4WD's championship success. The lineage of the HF 4WD — succeeded by the Integrale, 16v, Evoluzione, and Evoluzione II — became one of the most celebrated in rally history.