Lancia Delta S4 Gr. B Gravel

When the FIA Group B finally took life all the previous Group 4 cars resulted out of date and all manufacturers had to create something new for the homologation in the new rules that allowed much more freedom. Lancia at that time was running with the Stratos that in 1982 was substituted by the 037 Rally. It was very light and agile thus that in the 1983 it won the World Championship, the European and the Italian one.
But the Audi was optimizing its revolutionary racing 4WD system so that from the 1984 it was really difficult to compete against it with a simple RWD.
Lancia and almost all other manufacturers had to adapt their prototype to 4WD and indeed Lancia and Peugeot focused the target by creating 2 mid engine prototypes that for the rest of the time they lived made a series of battles that shone the heavy nose Audi a bit in shadows.
Lancia created the S4 (Sovralimentata, 4WD) that was basically an updated 037 with similar suspensions, a new spaceframe with lighter alloy and composite materials, a new 4WD drivetrain and a new powertrain. Lancia filed many patents for the S4.
Some reguarded the AWD system that used a transfer case to asymmetrically split the torque between the two axles while one reguarded the twin charging system that force the air induction with a compressor at mid-low engine speed and with a turbine at higher ones. As soon as the turbine has spooled up, the compressor was pneumatically bypassed, to allow the turbine to operate without thermodynamic efficiency losses typical of the compressor at higher rpms.
The first S4 official race was Algrave, Portugal in 31 October 1985 when Lancia hadn't produced yet the 200 street versions of the car requested to homologate the race one. The FIA anticipated its homologation to allow Lancia to participate to the championship that was starting but no one knows if Lancia has ever produced all the 200 "Stradale" models...
By the way, within 1985 and 1986, Lancia and other competitors, working on those and other technical innovations like tires compound and aerodynamic efficiency, raised safety and performance level of rally cars by several points.