The Saab B engine is based on the Triumph Slant-4 engine and replaced their aging two-stroke engine. When it was decided to develop a new Saab model in 1964, the Saab 99, the decision was also made to give it a modern four-stroke engine. A contract was signed with Triumph to deliver their soon to be complete 1.5 liter engine to use in the Saab 99. The engine was enlarged to 1.75 liters before delivery started, and later enlarged again to 1.85 liters.