That a Government department should issue a publication, copiously illustrated and covering 141 large pages, dealing with racing cars, is pretty staggering — certainly it is the first time this has happened and is, let us hope, a good augury for the future. The above-named publication is the technical report of the British Intelligence Objectives Sub-Committee inquiring into the German Grand Prix motor-racing teams, by Cameron C. Earl, who interrogated Herr Uhlenhaut and Director Wagner of Mercédès-Benz, Director Werner and Professor Eberan V. Eberhorst of AutoUnion, and Herr Hubenor of Continental Tyres.
The report is truly absorbing and brings to light many hitherto unrevealed aspects of this great period in motor-racing history. For instance, the cost of racing to the German firms is revealed — Mercédès-Benz and Auto-Union spent approximately £209,000 each per annum and received a State grant, authorised by Hitler, of £41,600 each. Auto-Union apparently hoped to race on this grant, but it is believed that additional armament contracts were given to the builders of successful racing cars, this possibly encouraging Auto-Union to continue in spite of their annual discrepancy of £167,400. Mercédès-Benz decided to race for purposes of prestige, probably egged-on by the knowledge that Auto-Union had purchased the P-Wagen design of Dr. Porsche.
Dr. Hans Nibel and Director Wagner, from Benz, led the design team which evolved the straight-eight Type M25 3.36-litre Mercédès-Benz, which was increased to 3.99 litres (M25B) before the end of 1934. After Nibel’s death Dr. Rohr modified the design but controlability proved inadequate in both forms. So the straight-eight Type M125 5.66-litre car was designed. In 1937, at Spa, it was timed at 193 m.p.h., which the B.I.O.S. says is the highest speed ever recorded in a road race. Wagner and Uhlenhaut were responsible for the Type M154 V12 3-litre for the new 1938 Formula, which was developed (as the M163), and in 1938 the 1 1/2-litre V8 Type M165 was designed. Auto-Union bought the 1933 P-Wagen after it had proved able to lap a specified circuit at over 120 m.p.h. Werner directed operations and Porsche joined Auto-Union, the first type being the 4.25-litre V16. Eberan was in charge of racing-engine work, and in 1935 the size went up to 5 litres, and in 1937 to 6, then to 6 1/2 litres. In 1938 6-litre sprint cars were evolved, and for the 1938 Formula a 3-litre V12 was produced. Eberan began work on a 1 1/2-litre V12 engine in 1939 but the car itself was never built. [The actual engine sizes and sequence do not tally exactly with former accounts of Auto-Union development. — Ed.]
The B.I.O.S. report gives a detailed account of the technical features of all these classic racing cars, quotes the views of the rival concerns on front versus rear engines and other matters, and details some of the development and design problems in the cars involved.
It is most interesting to learn that Mercédès could not use a compression-ratio higher than 7.5 to 1 because their cylinder construction invited joint failure, and piston crowns also collapsed. Their S.K.F. split-roller bearings suffered disintegration of the duralumin cages, and piston rings needed frequent replacement. Incidentally, high-speed photography assisted analysis of cam forms and valve springs. Apparently Auto-Union did far more bench-testing than Mercédès, the latter’s engines breaking up if run at full throttle sufficiently long for figures to be logged. The complicated D.B. carburetter was used by Mercédès only because the British S.U. was not available in Germany. Roots blowers were favoured because vane-type compressors seized their vanes. Had war not put an end to racing, future development would have been concerned with V12 or V16 engines running at 10,000 to 12,000 r.p.m., possibly using Wankel rotary valves. Only the Type M165 ran at a decently low temperature.
It is remarkable that both Mercédès and Auto-Union avoided the adoption of any feature, even though technically superior, normally associated by the public with their rival organisation — which is possibly why Mercédès eschewed Porsche suspension. Uhlenhaut disliked friction shock-absorbers and when he took over, after the 1936 season, specified double-acting hydraulics. From 1934 onwards Lockheed hydraulic brakes were used.
Auto-Union employed higher supercharger pressures and compression ratios than Mercédès and got more power out of their 3-litre. They, too, experimented with rotary valves and vane-type superchargers, having considerable success with the latter.
Whereas Mercédès made racing components in their main machine shop, under absolute priority, and had drawings made in the main drawing office, Auto-Union had a self-contained racing organisation, sadly lacking in funds, however. During a season Mercédès had 220 men, including two teams of 25 racing mechanics, in the experimental shop, and 1 1/2-litre development fully occupied eight or ten draughtsmen for three to four months. In 1939 Mercédès-Benz possessed ten M163 cars with ten spare engines, and two M165s with three spare engines. Eight large diesel lorries, one equipped as a mobile workshop, and a supercharged lorry for fetching urgently-needed spares, were employed, and to each race went the team, a reserve car, a practice car and several spare engines. The practice car incorporated any experimental features needing test. A doctor was shared jointly by Mercédès-Benz and Auto-Union, and specialists from Continental and Shell accompanied the teams; the former did the tyre wear and temperature tests, not the car personnel, nor were carburetter settings varied to suit atmospheric conditions.
Auto-Union could only afford 200 men in the racing shops and a foreman, and three mechanics to accompany each car to a race. One reserve car and one or two spare engines went also, but no practice car; the workshop lorry was far less elaborate than Mercédès, but four reserve cars were kept at the works. The workshop was at Chemnitz, under Dr. Seibler and four specialist engineers, and Eberan had two racing engineers under him at Zwickau, Saxonia.
This B.I.O.S. report gives an immense amount of data on the cars, including suspension details, valve timing and fuel mixtures. It is well worth its high price to keen engineers and anyone engaged in designing or building a racing-car or sprint “special”; indeed, it should be purchased by everyone who can afford it — in this way officialdom may be rewarded for issuing this absorbing publication on motor-racing. Specifications are given for each of the Mercédès-Benz types and for the 3-litre Auto-Union; b.h.p. and other figures differ slightly from those quoted elsewhere by such authorities as Pomeroy, Monkhouse and Jenkinson, but as several obvious lapses on the part of Government typists were not corrected before the pages were photostatted, it may be that some of the figures have suffered at their hands.
Space forbids further quotations from this intriguing report, but, as the 1 1/2-litre Mercédès-Benz tallies in size with presentday Formula I cars and points to what our B.R.M. must surpass, some facts relating to it are worthy of study — remember, however, that the Type 158 Alfa-Romeo is a more advanced car. A scaled-down M163, it gave 278 b.h.p. at 8,250 r.p.m. with a two-stage Roots blower running at 1.25 times engine speed and blowing at 2.6 A.T.A., and a 6.99 to 1 compression ratio. 18-mm. plugs, 100 per cent. glycol cooling pressurised at 1.5 A.T.A., and a 6-mm. inlet valve lift were employed. Oil and water temperatures were 85 deg. C. There were four valves per cylinder, inclined at 56 deg., and 12 litres of oil were carried. The brakes were lined with lurid BA (similar to Ferodo 9) and had 3.5 per cent. nickel drums with alloy fins. Their diameter was 12 3/4 in., width 2 1/2 in. 6.00-17 rear and 5.00-17 front tyres were used; the wheelbase was 8 ft. 0 1/2 in., and with driver and 55 gallons of fuel the total weight was 17 1/2 cwt., distributed 46.7 per cent. front, 53.3 rear. With Tripoli ratios, speeds at 8,000 r.p.m. were equivalent to 56, 97, 115, 146 and 170 m.p.h., respectively, in the five gears provided. — W.B.