Though Velocette’s KTT series bikes dominated the 350cc Junior class at the Isle of Man TT through the 1930s, the company lacked a suitably competitive bike for the Senior (500cc) class.

By the late 1930s, the most successful Senior machines were supercharged multi-cylinder motorcycles, with the BMW 255 Kompressor the one to beat. To meet this challenge, Velocette designed a unique parallel twin, single overhead camshaft engine with shaft drive. Two side-by-side contra-rotating crankshafts were geared together to balance out vibration, with a central bevel drive to the overhead camshaft. Air/fuel mixture was fed from a supercharger mounted behind the engine to the front of the cylinder heads, with the exhaust exiting to the rear.

Though the design called for the heads to be liquid cooled, the prototype was built with air cooling. It showed considerable potential, producing an initial 54hp (the BMW was rated at 60hp), and Stanley Woods was entered to run the Roarer in the 1939 Senior TT. But the engine overheated in practice, and Woods rode a KTT to 4th place instead.

WWII interrupted further development of the Roarer: and when GP racing resumed in 1949, superchargers were banned. Of the single prototype it was said that it “steered like a dream and was turbine smooth.”

  • 495.8cc (68mm x 68.25mm), SOHC, 2 valves per cylinder, hairpin valve springs
  • Geared contra-rotating crankshafts
  • Compression 7.5:1, boost pressure 4psi
  • Four speed gearbox, shaft drive

Dan Smith of Vancouver. Owner, designer and builder.

2.5 years and hundreds of hours.

Ivan Rhodes has the original in England.

Hastings Foundry poured castings from wood patterns made by Dan.

Murray Niebel for many miscellanies parts.

Fourth project by Dan following his 1936 AJS V-Four, 1912 Minneapolis and the 1939 Vincent model A Twin.