The DBR1 was initially fitted with a smaller 2.5-litre (2493 cc) new all alloy racing engine (RB6.250) very loosely derived from the racing version of the Lagonda Straight-6 engine to comply with that year's Le Mans 24 Hour regulations whilst the RB6.300 Straight-6 (2992 cc), rated at 250 horsepower was developed for the 1957 season.