THE ULTIMATE SILVER ARROW
n hindsight, the fundamental flaw in the
750kg Formula rules used for grand prix
racing between 1934-’ 37 was that they
didn’t take into account the sheer mass of
intellectual firepower and engineering
might that Mercedes-Benz and, to a
slightly lesser extent, Auto Union would
bring to bear in their quest to dominate.
The theory behind the formula was
simple yet (apparently) brilliant: By setting a
maximum car weight of 750kg (1,653lbs),
minus driver, fuel, oil, coolant and tires, you
naturally limit engine size and, therefore,
power. If a manufacturer was able to build
an engine big enough to put out, say,
225hp, yet still come in under 750kg for
the whole car, then well played, sir. And a
top speed of 150mph-plus? Bravo to that.
In reality, however, the advances and
innovations in combustion technology,
forced induction, metallurgy and lightweight
construction techniques pioneered by the
two German factories rendered the concept
a mockery. By 1935, Mercedes’ W25 was
already producing almost 500hp from its
guzzling, supercharged inline- 8, and
reaching speeds in excess of 190mph.
In the fall of 1936, grand prix racing’s
governing body, l’Association International
des Automobile Clubs Reconnus (AIACR),
attempted to put the genie back in the bottle
by limiting engine size to 3-liter supercharged
or 4.5-liter naturally aspirated for 1938.
Continuing down the supercharged
route would be Mercedes’ eventual choice,
but first there was the small matter of
1937, the final season of 750kg Formula
racing, and a chance to take its revenge
on Auto Union after a lackluster ‘ 36 with
a short-wheelbase version of the W25.
For 1937, the Three-Pointed Star
unleashed the W125, the first design
overseen by Rudolf Uhlenhaut. Its inline- 8
M125 was pushed out to 5. 6 liters by
in-house engine wizard Albert Heess, with
the supercharger fitted downstream of
the carburetors to compress the final
mixture entering the cylinders, not just the
air charge. The result was a staggering
600hp – if it could be used efficiently.
The elegant packaging of the 1939 Mercedes-Benz
W154 is testimony to the attention to detail of engineers
Rudolf Uhlenhaut and Max Wagner. However, note how
the saddle tank behind the engine and the main tank
that fills most of the rear section form a “cocoon” of
alcohol-benzene-gasoline fuel around the driver...