FOUR AIR COOLED 375 c.c. ENGINES IN A CAR FRAME
IT has long been known by racing-car engineers that the air-cooled single cylinder motor-cycle engine has unquestionable advantages from. the viewpoint of sheer power/capacity ratio. Partly this is due to the very efficient head formation possible with this type of engine, and other factors are the pumping efficiency of a single cylinder engine, even cooling, low mechanical losses and, especially, the rigidity of the crankshaft. 500 c.c. singles that produce 40 h.p. in unblown form are not unknown, and thus there is the attractive proposition of a 1i-litre combination developing 120 b.h.p. without recourse to supercharging, and with a saving in weight of cooling jackets, cooling water, complicated castings and manifolds, etc. So far no one has experimented very extensively in this direction, although Waddy’s Fuzzi 9 has two separate 500 c.c. engines, actually installed to assist with the four-wheel-drive employed, and Richard Bolster is using four Rudge single-cylinder engines in a G.N. frame. John Bolster’s work also conies to mind, though in this case Vtwin motors are employed. Some years ago A. F. Ashby introduced his carburetter-per-port four-cylinder , Riley engine, but it is doubtful if this engine,
with its two-bearing crankshaft, approached single-cylinder rigidity. Now C. E. C. Martin has announced his Martin Special, on which work was commenced in November, 1936. In the old 2-litre G.P. Delage chassis four dirttrack J.A.P. air-cooled single-cylinder engines are installed, each engine linered down to 375 c.c., putting the car in the 1i-litre class, The engines are located as a square, and coupled by gear-trains, chain-drive having proved unsatisfactory. Each engine has its own B.T.H. magneto. Lubrication is by separate oil pumps from a four-gallon (approx.) scuttle tank, and is dry sump. The engines have roller bearings throughout, bronze heads, and push-rod valve gear. Thirty gallons of fuel are carried in a rear tank, feed being by a Bugatti plunger pump driven by cant from the gear train. In the case of the Martin Special forced induction is used, a Roots blower being driven by roller chain from the engine coupling shaft at just above engine speed. It draws from an S.U. carburetter and blows at about 5 lb. per square inch, the engines having a compression ratio of 7 to 1. These figures may be varied after experimentation. Cooling is a major problem. There is a large aperture in the front cowling, and air scoops on the bonnet top direct a flow of air onto each cylinder head. The drive is taken to an E.N.V. self
changing a and thence by open shaft to a bevel rear axle. The front axle is from a monoposto Alfa-Roinco and the brakes have special 15i” steel lined Elektron drums and Girling actuation. Hartford shock-absorbers are used all round with Telecontrol at the rear, The worm and segment steering box is part of the old Delage, but Alvis, Austin, Hillman and other components are incorporated in the construction. The car has been out on Brooklands for testing and is rumoured to be very potent. One trouble has been excessive vibration at 4,000 r.p.m., rendering driving an uncomfortable occupation, but one hopes that this will soon be over
come. Charlie Martin deserves full credit for his enthusiasm in committing a remarkably interesting experiment, after ownership of such well tried racingcars as Bugatti, Alfa-Romeo and E.R.A., and for building up the special car in such a workmanlike manner. The Martin Special is intended for short races, sprint events and hill-climbs and its showing in such events will add interest to future fixtures.