By 1934 ‘Bert’ Bertelli had the best part of 15 years’ racing experience with some considerable international success. The ‘Ulster’, two seater racing version of the ‘Mark II’, was to become one of the most successful British sports cars of the 1930s. The works had a well appointed competition department, which was staffed full time by the most experienced men working for the company. The first three new team cars, LM11, 12 and 14 (there was no LM13) were carefully designed as simple but functional sports cars, using all the experience gained from the previous six years of racing. They had significantly lightened chassis frames, with upwards of seventy holes drilled on every face of the frame. In addition, light weight magnesium alloy was used for all non-ferrous castings. The timber frames for the bodywork were lightened by sculpting out the outer face, so that it could not be seen when the timber was skinned. The gauge of the aluminium used to clad it was also the lightest possible. Bertelli knew that his cars were relatively heavy and that the power to weight ratio of a racing car was all important.
The front axles (un-sprung weight) were given special treatment, with each face of the axle beam milled and the stub axles milled and drilled, so that both were significantly lightened. Wherever possible on every bracket (including engine mounts) and component, efforts were made to reduce weight. As with previous team cars, much use was made of lightweight magnesium alloy, which replaced aluminium for such components as brake back plates and shoes, bulkhead plates and engine fittings.
Gearbox and final drive ratios were also carefully chosen depending on what performance might be available from each car, of course depending on its weight and power. All the racing engines had been tested on the dynamometer and so Bertelli knew which of the three cars had the most power and torque.
However, apart from the lightening, the fundamental chassis and running gear were almost identical to the road going touring short chassis ‘Mark II’. The racing engines were given special treatment, with stronger crankshafts, high compression domed pistons and high compression cylinder heads with beautifully polished ports. Some experimentation was carried out in the design of the inlet manifold. The early team car LM14 had a semi down draught manifold, but later cars went back to side draught, the carburettors mounted on beautifully cast inlet manifolds with extended ports and secured to the high compression cylinder heads with stronger studs and nuts. These improvements, combined with a new higher lift specification camshaft (R209), twin 1⅜" SU carburettors and the 4 branch exhaust system, meant that the engines were persuaded to produce 85 bhp at 4750 rpm, close to 100 bhp at just over 5000 rpm, which is the maximum they were capable of for short periods of time. However a practical rev. limit had to be set for long distance races as it was well known that the ‘Dural’ connecting rods, even though they had been progressively strengthened over the years (across the caps between the bolts), were more than capable of breaking and punching a hole through the side of the cylinder block.
Bertelli’s many years’ experience of motor racing meant that the attention to detail on the works racing cars was second to none. The ‘Ulster’ had very comfortable deep bucket seats with a pronounced rake. This gave an almost perfect ergonomic angle for the back and particularly good lumbar support, which gave the driver as much comfort as he needed. Since driving these heavy cars without any mechanical assistance to the steering, clutch and brakes was quite hard physical work, during a long distance race this small detail could mean the difference between a reasonably fresh and alert driver and a dangerously tired one. Furthermore, he had the dashboards and the radiators of the works ‘Ulsters’ painted, just in case at dawn on the Mulsanne straight at Le Mans the sun might glare off a chromed radiator, or in the evening, a low sun might reflect off an aluminium dashboard. The ex military (ammunition box) quick release bonnet strap catches were also adopted on the third series works cars and became a characteristic feature on the production ‘Ulster’.
As the works racing team ‘Ulster’ was developed over a two year period, so the radiators got smaller. This effectively reduced the frontal area and the shape of the car back to the rear of the scuttle and as a result the bonnet required a ‘power bulge’ on the right hand side to accommodate the carburettors. Aerodynamic bodywork was tried on a couple of cars, with nicely shaped fairings behind the shock absorbers feeding into the side valances. A full under tray, from the front of the engine to the very rear of the car, also helped aerodynamics. No doubt useful for the time the car was running at speed (which was of course the purpose of the exercise), it was however also a real nuisance in the pits, for example if the clutch needed adjusting.
Furthermore, a few almost hidden details made these works’ cars special. The throttle and advance and retard levers were all carefully fabricated in steel rather than cast brass, and the oil filter had a simple ratchets attached to the spindle beneath the handle and linked to the clutch pedal by a rod and yokes, so that every time the clutch was operated the oil filter cleaned itself. Lastly the later cars had some very special lightened components. The countershaft which drove the oil pumps was beautifully machined, being taper bored down the length of the diameter which was supported by the rear bush. The timing gears, gearbox gears and shafts were all drilled and bored and even the kingpins were taper bored and the kingpin bushes cross drilled.
For the 1934 Le Mans race, it was LM14 that was lightest and most powerful. So, this car had the longest axle ratio to maximize top speed on the long straights of the circuit; the hope being that they could break one or two of their closest competitors if they tried to chase the ‘hare’. Sadly, this strategy was not played out as, in the event, all three works cars had reliability problems during the race which, had it not been for two privateer entries in older cars who did finish, would have been a complete disaster.
However, the basic design of the ‘Ulster’ was sound and the reliability issues suffered during the 1934 24 Hours Race were to be solved. Shortly after Le Mans, Bertelli decided that the Ulster TT race would be the next major works effort, but this required three new cars. A recent rule change, to try to reduce the development gap between the work cars and privateers, meant that very few modifications to the standard car were tolerated, including lightening of the chassis. All three of the Le Mans cars, with drilled chassis, were therefore not eligible. Bertelli hastily transferred all the components from LM11 and LM12 to two new undrilled chassis (to be numbered LM15 and LM16) and built a third complete car (LM17). The results of the TT were much more encouraging, with the three works cars winning the team prize. This was the first race that the cars ran in ‘Italian racing red’ instead of the unlucky ‘Irish green’. Their success was trumpeted in magazine advertising and capitalized upon by calling the production model the ‘Ulster’.
1935 saw three further works team cars built and prepared; LM18, LM19 and LM20. The Le Mans effort was further bolstered by four works supported privateer cars whose drivers were eligible to enter for the Rudge Whitworth Cup, by virtue of their previous success (not necessarily in an Aston Martin). This was the biggest entry of Aston Martins in any single race by the factory and represented a huge effort, particularly since they had already that season actively supported two cars racing abroad, at the Mille Miglia and the Targa Abruzzo. The Rudge cup was duly won, with LM20 coming home third and breaking the lap record for 1½ litre cars at 81 mph, a speed that stood for fifteen years.
For the 1935 TT the works entered four cars, including what was to be the last 1½ litre team car; LM21. In addition, the works prepared a special car for B. Bira, identical to the works cars in specification, but painted Bira’s favorite blue and with lots of chrome. This was the last occasion that the works entered a team in an International motor race (though they did later support Jock Horsfall in a race by entering him as ‘Aston Martin Ltd.’) and sadly it was not an entirely happy experience. Bertelli had decided to change the specification of the oil pipes on the racing cars, uncharacteristically, without a great deal of testing. The decision was a disaster, as all four cars suffered from fractured oil pipes, which was particularly hazardous for a dry sump engine with all the extra plumbing that entailed. It was reported that Bira was especially annoyed, and that he gave Gordon Sutherland a very hard time at the pit counter while his car was being repaired during the race.
Bertelli was later to admit that this was the worst decision he had ever made, but he was also to state that the ‘Ulster’ was the best car that he ever built. The ‘Ulster’ was the last Aston Martin to be built and directly overseen by A. C. Bertelli. Over a two year period it had proved to be one of the best 1½ litre purpose built sports cars in the world and remains today one of the most sought after of all Aston Martins. All the works team cars survive and many are still actively used in competition, with the exception of the two dismantled TT cars (LM11 and 12) though LM12’s chassis survived by being used to repair the very first production ‘Ulster’ after a serious accident badly damaged the frame. The damaged frame of LM19 is also known to have survived, built into a production ‘Mark II’, leaving only the chassis LM11 missing, though intriguingly a further ‘Ulster’ was repaired post war with a drilled chassis very much like the three drilled chassis prepared for Le Mans in 1934.