Regulators designed the 750 kg limit to curb rising performance by restricting engine capacity indirectly. The prevailing assumption was that fitting a large, powerful engine inside a 750 kg car would require unacceptable compromises elsewhere, and that teams would gravitate toward engines of around 2.5 litres. The minimum cockpit width was set at 850 mm. There was no restriction on fuel type. The American AAA, facing similar concerns about increasing speeds, chose a fuel-consumption formula for the Indianapolis 500 instead.
The 1934 season was also a landmark in that the AIACR formally recognised the voiturette class with a 1,500 cc maximum, acknowledging a separate tier for smaller and less expensive machinery.
The formula's assumptions were overturned immediately by the two German manufacturers, Mercedes-Benz and Auto Union, who received state funding — an annual stipend of 250,000 Reichsmarks each — from the German government under Adolf Hitler's programme to promote German automotive prestige. Both entered Grand Prix racing in 1934 with advanced, purpose-built cars that exploited the absence of an engine capacity limit.
Auto Union's car, the Type A, was designed by Ferdinand Porsche based on his P-Wagen project. It used a supercharged V16 engine displacing 4,360 cc, mounted behind the driver in a rear-mid layout — a configuration virtually unique in Grand Prix racing. The car initially produced 295 bhp. Mercedes-Benz countered with the W25, designed by Hans Nibel, using a supercharged inline-eight of 3,360 cc producing 350 bhp. Both cars used lightweight tubular frames with independent suspension on all four wheels, in complete contrast to the rigid-axle designs of the established Italian constructors Alfa Romeo, Maserati, and Bugatti.
Engine capacities and power outputs grew substantially across the four seasons of the formula. Auto Union's V16 reached five litres in 1935, 370 bhp, and expanded to six litres in 1936, yielding 520 bhp and speeds approaching 258 mph (415 km/h). Mercedes-Benz peaked in 1937 with the W125, powered by the M125 engine: a supercharged 5,662 cc inline-eight producing between 560 and 595 horsepower at 5,800 rpm, the highest test bed reading reaching 637 bhp.
Exotic fuel blends became a key performance differentiator. The German teams used custom mixtures of methyl alcohol, benzene, ethyl alcohol, and a small proportion of light gasoline, formulated to withstand higher boost pressures without detonation. The fumes were powerful enough that mechanics and nearby spectators reported headaches, nausea, and respiratory problems.
Both German manufacturers adopted advanced suspension and chassis engineering, with Auto Union introducing a Porsche-designed limited-slip differential from ZF at the end of 1935 after testing revealed severe wheelspin on corner exit. Auto Union also developed clockwork-driven data recorders to capture engine rpm during test sessions, an early form of data acquisition.
Hans Stuck led Auto Union's first season in 1934, winning the German, Swiss, and Czechoslovak Grands Prix. For 1935, Mercedes-Benz driver Rudolf Caracciola took the European Championship. In 1936, Bernd Rosemeyer became European Champion in the six-litre Auto Union Type C, winning the Eifelrennen, German, Swiss, and Italian Grands Prix, as well as the Coppa Acerbo. Rosemeyer also took the European Mountain Championship. Between 1935 and 1937, Auto Union cars won 25 races.
In 1937, the final year of the formula, Mercedes-Benz won seven races to Auto Union's five. Caracciola won the European Championship for the second time. Richard Seaman, Manfred von Brauchitsch, and Hermann Lang contributed victories across the season.
By 1937 the speeds generated under the formula had become alarming. The average race speeds and outright velocities far exceeded what had been anticipated, and accidents at those speeds were regularly catastrophic. The AIACR replaced the 750 kg formula with a new set of regulations for 1938 that set a maximum engine displacement of 3,000 cc for supercharged engines and 4,500 cc for unsupercharged engines, while also introducing a minimum car weight. The six-litre German engines were immediately ineligible, and both Auto Union and Mercedes-Benz built new V12-engined cars for the 1938 season.
The 750 kg formula represented the first and most dramatic demonstration of what happens when engine capacity is left unconstrained in a weight-limited formula: manufacturers simply build the largest and most powerful engine the weight budget permits. The regulatory lesson shaped subsequent Grand Prix rules and, much later, contributed to the detailed capacity, boost, and fuel-flow limits of modern Formula 1 power unit regulations. The cars of the 750 kg era — particularly the 1937 W125 — were not surpassed in outright power by any Grand Prix car until the turbocharged engines of the early 1980s, nearly half a century later.