The first six-cylinder Volvo engine was ready in 1929. The first car to be equipped with the DB engine was the PV651. The engine had a capacity of just over 3 liters and the output was a modest 55 bhp. It was a strong and flexible unit, two properties that characterize the in-line six as a technical design.
The PV651 and its successor, the PV652, were both longer and wider than previous Volvo cars. All four wheels were given four-wheel brakes as standard, either mechanically (PV551) or hydraulically (PV652) operated.