Like Peugeot's earlier 205 T16, the mid-engine Lancia Delta S4 was a Delta in name and body styling only (for marketing purposes), and shared virtually nothing in terms of construction with the production front-engine Delta. The chassis was a tubular space frame construction much like the 037. It featured long travel double wishbone suspension front and rear, with a single large coil over at the front and separate spring and twin shock absorber at the rear. The bodywork was made of a carbon fibre composite with front and rear bodywork fully detachable for fast replacement due to accident damage, allowing ease of access during on-event servicing. The bodywork featured several aerodynamic aids including bonnet opening behind the front-mounted water radiator with Gurney flap, front splitter and winglets moulded into the front bumper panel, flexible front skirt, and rear deck lid wing that featured both a full aerofoil wind section twinned with a deflection spoiler. The door construction style was brought from the 037 with a hollow shell all-Kevlar construction that had no inner door skin, no door handle or window winder. The door was opened with a small loop and the windows were fixed perspex with small sliding panels to allow some ventilation and passing of time cards and suchlike.
For homoligation processes, Lancia also built a claimed 200 Delta S4 Stradales in the mid-1980s; a road-going version of the Group B monster. However, records suggest that only around 65 cars were ever produced, with 20 being destroyed or converted to competition-spec for privateer racing. Although power was reduced to around 200bhp, the car retained the twin-charging of the rally-car. In fact, many stradales were taken into competition by their owners, especially as boosting power from the 4-cylinder engine was an easy procedure.