The Velocette ROARER : (1939)
A supercharged twin cylinder racing bike aimed at winning against
the supercharged contemporary BMW.
One single prototype was manufactured.
2 vertical cylinders, 4 stroke, OHV, 2 carburators
2 parallel contra-rotating crankshafts, geared together
(a technical layout which will inspire the Model O)
Cylinder : 497,7 cc (Bore : 68 mm ; Stroke : 68.25 mm)
Compression rate : 8.78/1 then 7.5/1
Boost pressure : 4 psi
Measured engine power : 54 bhp
3 plate clutch
4 ratio gearbox
I think the new pictures are a replica build but I'm not sure.
Go read the Velobanjogent blog to find out! :)