Clara was just another brilliant 350cc racer from Velocette, but was down a bit on the Rudge and Norton factory boys. So young Mr Willis wondered what a little huff would do to the equation. And Harold being Harold, he took a shop vacuum cleaner, plumbed the outlet into a box he built on Clara's inlet side, and saw the BHP go up 30%.
So the next thing anyone knew, Clara had a super-charger at the front, and a great big semi-triangular plenum at the back (clearly shown on the RH side with a pop-off valve leading to the carb). And it needed that big plenum, because single cylinder engines are notoriously hard to super-charge, what with the inlet valve being closed more than it is open, so things tend to get a bit confused, with the blower constantly under and over pressurizing the intake charge.
But a large plenum would smooth all that out, and would always deliver a nice pressurized dose of goodness whenever the inlet valve got around to opening. And when the Inlet was closed, it would keep the pressure spikes manageable and allow excess pressure to be bled off smoothly and safely.
But it made a whiffling sound something fierce, especially after being shut down after a hot run and the pressure in the plenum bled down. "Whiffling Clara" it was then.
