With cash-strapped Rootes struggling amid continuing engine cooling problems with the Imp, which often resulted in warped cylinder heads, the cautious Arrow broke little new engineering ground. New parts were largely based on tried and tested Rootes components, using a new but strong 5-bearing version of the well-proven 1725 cc overhead valve petrol engine as a starting point which varied in output from to (in the Humber Sceptre). The engine was inclined by a modest 15 degrees, to allow for a lower bonnet line and to enable packaging of the carburettors. This engine was further uprated by specialists Holbay, employing two Weber 40DCOE carburettors to produce for the Sunbeam Rapier H120 and Hillman Hunter GLS. A smaller 1500 cc engine was the standard for manual versions of the Hillman Minx and the Singer Gazelle, and the Hillman Hunter DeLuxe model which succeeded the Minx. Automatic models were all powered by the 1725 cc engine. Particular attention was paid to weight and cost to bring the vehicle in line with its natural competitors, including the Mark 2 Ford Cortina.