THE TRIUMPH ” DOLOMITE “
A SUPERCHARGED TWO-LITRE SPORTS CAR WITH A GUARANTEED SPEED OF 100 MILES AN HOUR
THE production of supercharged sports cars other than those of small capacity has for some time been neglected by British manufacturers, and the announcement of the Triumph “Dolomite,’ which took place shortly before the Motor Show, was a particularly interesting one to sportsmen who want to travel fast and yet “Buy British.” The car has been produced as a fast yet tractable touring vehicle, fully equipped and not tuned for racing, but the Triumph Company offer a close co-operation to any amateur who wishes to enter his car for this branch of the sport.
The engine is, as ever, the heart of the motor car, and the designer of the Dolomite engine has taken full advantage of the light alloys developed through aircraft research to produce a light though robust power-unit, The eight cylinders are cast in two blocks of four, bolted together in line,and enclosing between them the train of gears driving the two overhead camshafts. The cylinder head is detachable, and the valves are inclined to one another at 90 degrees, in hemispherical combustion chambers, with centrally disposed sparking plugs. The cams bear directly on to the valves, which have each three springs, and the clearances are adjusted by screwing round the threaded caps. Each camshaft is carried in six bearings.
The cylinder dimensions are 60 by 80 nim., giving a capacity of 1,990 c.c., and an R.A.C. rating of 17.8 h.p., and next year the car will be taxed at £13 10s. Od. The cylinder head and block are made of R.R. Hiduminium, a light alloy of wellproved strength ; while steel insets are pressed into the head to act as valve seatings, and nitrogen-hardened steel dry liners are used in the cylinder block to provide a working surface for the pistons. rhese are also made of Hiduminium, with domed crowns. Steel connecting rods are used, with plain big-ends. Elektron is used for the crank-case and the ribbed
sump, and for other small components such as the valve covers.
The crank-shaft, like the cylinder block, is built in two sections, each carried in five plain bearings. The sections are connected together by a spring coupling, which also carries the pinion driving the train of skew-cut gears for the camshafts. It will be recalled that this form of construction is employed on the 2.3-litre Alfa-Romeo. The crank-shaft is fully balanced, with disc webs, and also embodies a torsion damper.
A Roots type super charger is mounted on the offside, and is driven from the central gear train, and the dynamo is mounted in a corresponding position on the other side. On the first Dolomite engines the super charger drew its mixture from a two-choke Solex carburetter, but as difficulty was experienced in silencing the air intake, a down-draft S.U. will probably be the final choice. The fuel is supplied by a duplex electric petrol pump, the compression ratio is 6.5 and the blower pressure is 10 lbs.
Coil or magneto ignition are listed as alternatives, and the distributor or magneto is mounted vertically, and driven by skew gears from the front end of the crank-shaft. Lubrication is, of course, a vital point on any high-efficiency engine, and on the Dolomite the dry-sump system is used. The oil is forced to all parts of the engine by one section of a double pump, while the other forces the hot oil through a ribbed elektron tank, which holds three gallons, mounted between the front dumb-irons. The engine is designed to run up to 5,500 r.p.m., and is rated to give 140 h.p. A large Armstrong-Siddeley selfchanging gear-box the casing of which is made of elektron is mounted on a bellhousing at the rear of the engine. A clutch is not fitted, but to relieve the engine of sudden shocks, which may be brought about by an. abrupt change of gear, a rubber ” Cush-Drive ‘ is fitted to the rear of the flywheel. An internally
serrated housing is carried on the flywheel and an externally serrated one on the gear-box shaft, the space between fingers being occupied by rubber blocks. With a four to one back axle, the overall ratios are 12.4, 7.4, 4.92 and 4.1 to 1, which should allow about 90 m.p.h. in third gear ! The gear-control is of the usual quadrant type mounted on ‘the steering column, while the double oil pump keeps the internals of the gear-box in good condition. An open propeller shaft is used with two needle-bearing universal joints.
The back-axle is of normal type, with spiral bevel final drive, ratios being either 4.0 or 4.5, according to choice. Two hydraulic shock-absorbers are mounted on each side of the back axle, and help to take the torque, while if the car is supertuned for racing radius rods will probably be fitted.
The front axle is light and beautifully made, rectangular in section between the springs, and rounded at the ends, where it has to take the braking torque. Radius rods run back from the spring mountings to the chassis, and friction type shock absorbers are used. All the springs are fiat semi-elliptics, and the front ones have special rebound leaves.
The chassis is quite light in construction, and is made of special high-grade nickel steel, slightly upswept in front and rising abruptly where it clears the back axle. The front part is rigidly braced by the front tie rod, a cross member behind the radiator and the stiff box construction of the crank-case, which is bolted at the rear directly to the side members. There is a light member behind the gear-box and a stiffer one at the front end of the rear springs, bridged by a light centre girder. and it is to this carefully arranged flexibility at the rear end of the chassis that Mr. Healey, the well-known competition driver, who is now in charge of the Triumph sporting department, attributes its exceptional road-holding. The petrol tank is supported on rubber at three points and holds 20 gallons.
Last, and not least, we come to the magnificent I6-inch brakes, with their finned elektron drums. Steel liners are used, pressed in and rivetted in position, while the brake shoes, which are lined with Ferodo, are made of Hiduminium. The brakes are hydraulically operated, and the front set have larger cylinders than those at the rear, in order to secure the correct proportioning of the braking effort.
By the extensive use of light alloys the weight of the chassis has been kept down to 14 cwts., while fully equipped and fitted with a neat two-seater body the Dolomite turns the scales at 19 cwt. The ground clearance is 8 in., the wheel-base is 8 ft. 8 ins., and the track is 4 ft. 6 in. The chassis is priced at £1,050 while the car complete costs £1,225.