Miss Tilly and her Orifice

When I was quite a young girl, Grandfather Edgar had the idea to fit a supercharger to a 500cc Blackburne engine he had somehow acquired, and for which he was building a frame to take part in sprint events.  I remember he had purchased a Shorrock unit but wasn't quite sure about ratios and mixtures and so on.  "I need help to get a blow job, Camilla," he would say, laughing away in that deep rumble of his.  I didn't then know how rude that was - not the thing to say to a young girl, but that was Grandad!

Of course, he knew great motorcycle tuners like George Brown and Noel Pope but was anxious to take his own route.  He gained an appointment to see Professor G F Mucklow, the Head of Mechanical Engineering at the University of Birmingham, and who had carried out a lot of research into supercharged single-cylinder engines. I was very excited when Grandad said he would take me along - I think he had an idea that it would inspire me to go to University.  Grandad explained what he was trying to do, and Professor Mucklow listened carefully before smiling and saying, "You should really be talking to my former assistant, Doctor Shilling.  She knows all about superchargers and fuelling - and motorcycles!"  Grandad wasn't often stopped in his tracks. "Do you mean Tilly Shilling?" he said at last. "I raced against her at Brooklands!" And that was indeed who the Professor meant.

Beatrice Shilling OBE, PhD, MSc, CEng was a highly talented aeronautical engineer - and motorcycle racer, gaining a Gold Star at Brooklands for her 106mph lap.  She became hugely famous when she found an elegantly simple cure for the engine cutting-out problems experienced by Spitfire and Hurricane pilots when making extreme turns.  It was a simple fuel-restriction device, like a washer with a needle valve, that was fitted into the SU carburettor and solved (nearly) the problem until pressurised carburettors were fitted to the Merlin engine.  The little device became known as "Tilly's orifice" - and many of our brave fighter pilots owed their life to it.

Many years later, I purchased an old Leyland Beaver truck to use as my race transporter - and Grandad suggested we fit a Merlin engine to it, like John Dodd had done with a car he called 'The Beast' - but we had problems getting it to run cleanly.  I wrote to SU Carburettors asking if they had any pictures of Tilly's Orifice, and explained it was because my Beaver was running badly.  I had a letter back from some person called Paul Burman that was so rude that I threw it away.