The car's Inline-four engine combined supercharging and turbocharging to reduce turbo lag at low engine speeds (rpm). The engine generated a maximum output of but some sources even claim that the engine was capable of generating . In 1985, when Lancia engineers tested an S4 engine under extreme conditions, it developed around at 5 bars of boost pressure. An engine capacity multiple of 1.4 was applied to forced induction engines by the FIA and the choice of put the S4 in the under 2,500 cc class, which allowed for a minimum weight of . The combined super/turbocharger system (often referred to as twincharging) was a development of the 037 engine that generated with a supercharger only.