de Havilland Gipsy Queen 30

 The de Havilland Gipsy Queen is a British six-cylinder aero engine of 9 litres (550 cu in) capacity that was first run in 1936 by the de Havilland Engine Company. It was developed from the de Havilland Gipsy Six for military aircraft use. Produced between 1936 and 1950, around 5000 Gipsy Queen engines were built.
The engine was used in numerous British aircraft and in an Italian Air Force trainer. This intermediate trainer, the Fiat G.46, was the first new model produced by Fiat after WW II and was test flown in 1947. Argentina received 70 aircraft of the G.46-2B model powered by the 250 hp de Havilland Gipsy Queen Srs.30, the first being delivered in 1949, the last in 1951. The Museum’s example is believed to be a licence-built model built by Fiat.
Early versions had an output of 205 hp. In 1946 the all-new, 240 hp, Gipsy Queen 30 was introduced. The later Gipsy Queen 70-3 was rated at 380 hp (280 kW) and incorporated a supercharger with a reduction-gear drive.
The engine was used in the de Havilland Dove, Dragon Rapide and Heron. It was also used in the Handley Page Marathon, Miles Mentor and Merchantman, Percival Prentice and Proctor, the Short Sealand amphibian.
The engines were of particular note for their exceptionally low cross-sectional area, a drag-reducing feature which made them ideal for the many racing aircraft of that period. In 1934, the basic bronze-headed Gipsy Six, rated at 185 horsepower (138 kW) at 2,100 rpm was modified for use in the DH.88 Comet air racer as the Gipsy Six "R" which produced 223 horsepower (166 kW) at 2,400 rpm for takeoff.
For more on this family of engines see:

Technical Details (Gipsy Queen I)

Type: 6-cylinder inverted inline piston engine
Bore: 4.646 in (118 mm)
Stroke: 5.512 in (140 mm)
Displacement: 560.6 cu in (9.186 L)
Length: 63.5 in (1,587 mm)
Width: 20.5 in (513 mm)
Height: 33.5 in (838 mm)
Dry weight: 486 lbs (220 kg)
Valvetrain: Overhead valve
Fuel type: 87 octane petrol
Oil system: Dry sump
Cooling system: Air-cooled
Power output: 208 hp (155 kW) at 2,400 rpm
Compression ratio: 6.5:1
Power-to-weight ratio: 0.43 hp/lb (0.7 kW/kg)
Gipsy Queen 30
All-new engine from this point. (120 mm x 150 mm = 10.18 L)
(1946) 240 hp (180 kW), 1,762 built.