What do you do if you're comfortably on top of the rallying world with a dominant car that revolutionized the sport? Well, if you are the Fiat Group, you abandon it to race a new one based on a humble and decidedly unsexy family sedan, then you go winning the world championship with it. Three times.
Our story begins in late 1974 when the men at Fiat's racing division Abarth saw their project for a rally weapon based on the mid-engined X1/9 abruptly canceled.
Fiat's higher-ups preferred the image boost from sporting success to benefit a volume seller rather than a niche sports car, so, much to their dismay, Abarth's men were ordered to start again from the then-recently introduced 131 family sedan.
The replacement for the popular Fiat 124, the 131 was offered as a four-door sedan, a station wagon but also as a two-door sedan, never a popular configuration in Italy but one that was instead favored in important export markets like Germany.
Technically and aesthetically conservative to a fault, excitement was never part of the brief for the 131, but that didn't deter Abarth's engineers.
Fiat's racing department settled for a twin-cam inline-four-cylinder engine with four valves per cylinder: the latter being a first for a road-going Fiat model. Fed by a Weber 34IDF double-choke carburetor, it produced 140 horsepower on the road car, but in the racing versions equipped with Kugelfisher mechanical fuel injection, it could make between 225 and 245 HP. Power went to the rear wheels via a five-speed transmission and, on the racing cars, a ZF limited-slip differential.
To improve traction on the loose, bumpy surfaces typical of rallies, the live axle from the "regular" 131 was dropped in favor of a McPherson design similar to that of the X1/9 project.
The works of famed coachbuilder Bertone were entrusted with designing and constructing the bodies for the 400 road-going cars required for homologation. There, the standard two-door 131 bodies supplied by Fiat were extensively modified with resin body panels and aluminum doors to decrease weight and substantially larger wheel arches to cover the low-profile Pirelli P7 195/50 VR 15 tires.
Homologation in Group 4 was granted in April 1976, even though Fiat's dealer network would take the better part of two years to clear the stock of 400 cars produced.
Following two victories in the 1976 Italian rally championship, the Fiat 131 Abarth Rally took its first victory on the world rally stage at the 1000 Lakes Rally in Finland, driven by the Finnish ace Markku Alén.
But the 131 racing program also spelled the gradual phasing out of the Lancia Stratos while arguably still unbeaten, perhaps contributing to the latter's legendary status.
From 1978, the racing departments of Lancia, Fiat, and Abarth were merged into a single organization, with the Lancias initially confined to the European Rally Championship and then retired altogether, leaving to the 131 Abarth the task of winning the World Rally Championship.
This was a task that the 131, despite its humble family car roots, fulfilled very effectively indeed.
Three constructors' world titles between 1977 and 1980, countless placements and victories in the Italian and European circuits, the 1978 Drivers' Cup for Markku Alén, and the World Rally Drivers Championship won by Walter Röhrl in 1980.
By 1981 the 131 Abarth, much like the other rally cars of its day, was made all but obsolete by the revolutionary Audi Quattro. Moreover, Fiat was no longer interested in investing in the aging 131 and instead decided for a return of the Lancia brand to the WRC with a new car developed according to the new, more permissive Group B regulations that would come into effect starting from 1982.