In the early twenties Hispano Suiza introduced a new six cylinder model, the H6B. The H6B excelled in luxury and comfort but its light weight and powerful engine made it a very competitive in motor racing. In 1922 a special H6B won the Georges Boillot Cup race and a year later an updated 8 litre model repeated that feat.

This led to the introduction of 8 litre engine road cars dubbed H6C.

Birkigt had incorporated much of his aircraft engine technology into the H6 powerplant. The 6.5-litre in-line six had a one-piece aluminium cylinder block and an overhead camshaft. This was at a time when Rolls-Royce's venerable Silver Ghost was still using side valves, and an iron block cast in several pieces. The H6's massive crankshaft was carved out of a solid 317 kg (700 lb) steel billet.

In the early twenties Hispano Suiza introduced a new six cylinder model, the H6B. The H6B excelled in luxury and comfort but its light weight and powerful engine made it a very competitive in motor racing. In 1922 a special H6B won the Georges Boillot Cup race and a year later an updated 8 litre model repeated that feat.

This led to the introduction of 8 litre engine road cars dubbed H6C.

It was also ahead of Rolls-Royce in the braking department. While the Rolls had brakes on the rear wheels only, the Hispano had four-wheel brakes, servo assisted by a shaft driven off the rear of the transmission. Rolls-Royce later adopted this system under licence from Hispano and used it for many years.

The Hispano-Suiza H6 was fitted with some of the finest bodies available from the best coach builders. And although it was conceived as a luxury car suited to gliding along the Champs Elysees, or dashing down to the Riviera on the routes nationals, it was also raced on occasion.

Wealthy sportsman Andre Dubonnet, of aperitif fame, won a sports car race at Boulogne in an H6 in 1921, and repeated it two or three years later in the larger 8-litre Hispano, which was then appropriately named the "Boulogne."

The H6 was made in both 6.5 and 8.0 litre versions through 1934. In 1931 a massive 9.5 litre V-12 Hispano-Suiza was introduced. Alas, Birkigt's overhead cam had given way to overhead valves, and although the V-12 was quieter, it was not regarded by Hispano purists with quite the same awe as was the H6.