1937 Ariel Square Four prototype
Though a prototype 600cc overhead valve version had been developed in conjunction with the 1000cc version, it wasn’t listed until 1939. Bore size for the new 600 was 50.4mm, while the stroke remained unchanged from the 1000cc version, at 75mm. Though it weighed the same (a tubby 420lb) as the litre version, it had 13bhp less, at 23bhp.

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