The ultimate expressions of the original Midget engine, both used the 746cc cylinder dimensions and were supercharged. The J3 had a forged crank and a No 6A Powerplus blower, while the J4 was very heavily modified as an out and out racer. A new block with increased diameter head studs, a fully counterbalanced crank, a No 7 or 8 Powerplus blower running at up to 18psi boots and a redesigned induction system were used, while on the chassis front there was a J2 frame with C-type 'box and 12ins L-type brakes. J4 always had an excess of power over handling (72.3bhp engine mounted in the standard 86 ins wheelbase frame). The story of the J4 was concurrent with the story of the brilliant young Hugh Hamilton, and its best result was second in the epic 1933 TT. Both the J4 and the roadgoing J3 are very rare and very expensive - if you can even find one.