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To replace the 750 kilogram formula for Grand Prix cars
that expired at the end of 1937 the Sporting Commission
decreed, "from January 1, 1938 to December 31, 1940 that
maximum engine capacities should be limited to 3 liters if it
be supercharged and 4.5 liters if that adjunct to higher speed
was not employed."
With that edict the V-16 C-type Auto Unions, which had
run the 1934-1937 Grand Prix Formula became obsolete.
Professor Ferdinand Porsche had been responsible for both
design and development of the C-type’s 16-cylinder engine.
This basic 45-degree V-16 "grew" in displacement every
year, starting at 4358 cc and ending in 1937 at 6329 cc.
Over that four-year period, the output of this supercharged
engine nearly doubled: from 295 to 545. It shouldn’t be surprising
that the C-type, with its forward-mounted driving
position and mid-engine configuration, was prone to
extreme oversteer.
For 1938-1939 Professor Robert Eberan von Eberhorst
took responsibility for the development of the D-type Auto
Union from Dr Porsche. Eberhorst chose to design a 60-
degree V-12, supercharged and with a compression ratio of
10.0:1. With a 65 mm bore and stroke of 75 mm, the engine
displaced 2985 cc, producing 420 bhp at 7000 rpm the first
year and 485 bhp at 7000 the next. Maximum torque for the
more powerful version was 405 lb-ft at 4000 rpm.
These prewar Auto Unions are among the most technically
and historically significant grand prix race cars ever created.
Numerous articles and books have been written about
how they disappeared behind the Iron Curtain during the
war, of the tenacity of a variety of collectors to find and
save them, and the subsequent patience and skill of restorers
to bring them back to racing life again.
But our focus here is the technicalities and minutiae of
what is both a complicated and fascinating V-12 engine. The
engine block is of cast aluminum. The water jackets are
integral with the upper half of the crankcase. Wet liners of
forged chrome steel, deeply spigoted into the block and
sealed at their tops by the cylinder heads, provide the sealing
surface between the cylinder walls and piston rings.
Cylinder heads are aluminum with hemispherical (hemi)
combustion chambers. There’s more aluminum in the
forged-domed pistons, each with three compression rings
and an additional oil scraper ring. The link between pistons
and crankshaft is via H-section connecting rods of forged
nickel-chrome steel.
Nickel-chrome steel is also used for the components of
the Hirth-type crankshaft. Auto Union V-16s used plain main
bearings with roller bearings for the con rod big and little
ends. The V-12s used similar roller connecting rod bearings
and plain mains, except for a few engines with roller mains
to reduce friction and increase horsepower. And, unlike the
partially-counterweighted crank of the V-16, the last versions
of the V-12 crank were fully counterweighted to cope with
its much higher engine speeds.
To fully appreciate the complexity of the Mahle crankshaft assembly, it is educational to refer to an article by
Doug Nye in the January 1995 issue of Classic and
Sportscar. In this story on the restoration of two Auto
Union GP racers recovered from the Soviet Union, Nye
relates that one all-roller bearing Hirth-type built-up
crankshaft plus bearings and rods, which the restoration
firm Crosthwaite and Gardiner completely dismantled,
yielded 1,111 individual pieces!
Nye also comments on the exquisite design of each of
the individual tooth-together sections of the crank, which
enable roller bearings to be threaded over each connectingrod
big end during assembly. Disassembling them involves
internally-splined socket tools, which Crosthwaite and
Gardiner had to make, in order to release the carefully
ground, fine-threaded mating bolts. The crankshaft tail is
also a work of art. Its radial teeth lock into the flywheel
with a threaded scroll gear driving the oil pump, and a bevel
gear to drive the supercharger and camshafts.
For more on this article and much more grab a copy of Auto Aficionado Magazine on newsstands nationwide!
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