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Velocity Raptor
Each year, Continental Tires invites Europe’s top car tuners to southern Italy for its Nardo High
Performance Event. The competition is simple: The team that sets the highest top speed wins.
Modified Porsches have dominated the event, with other German brands usually filling up the rest of
the leader board. This year, however, an American car is vying for overall honors—a Chevrolet
Corvette Z06.
Munich, Germany’s Geiger Cars has been specializing in American vehicles since 1979. Though
it imports new and used cars and sells many of them as-is, Geiger is best known for its modified
machines—and it pulled out all the stops with the Corvette it brought to Nardo. The factory “Z06 505
HP” badges on its flanks no longer tell the truth: They are pessimistic to the tune of 385 horsepower.
While the Geiger Z06 Bi-Turbo’s claimed 890 bhp is bested by the 1,000 ponies of the 9ff-modified
Porsche 911 Turbo, the Corvette, with its lurid Kermit-green paint scheme, is definitely the most eyecatching
machine present. Will it be the fastest?
Speaking to one of the Geiger mechanics, we learn that the Bi-Turbo did not start off as an
official part of the Bavarian company’s Corvette tuning program. Instead, like the ZR1, it was
envisioned and built by a couple of engineers in their spare time. When the conversion was finished,
company boss Karl Geiger was so impressed with the car’s ballistic performance, he sanctioned its
use for publicity work, including this Nardo shoot-out.
Not surprisingly, the biggest changes to the car were made in the engine compartment. The stock
Z06’s hand-built 7,001-cc LS7 V8 is already a heavily tuned version of the standard V8, with forged
titanium connecting rods, titanium inlet valves and sodium-cooled exhaust valves. These racy
components allow this big engine to rev to 7,000 rpm, yet the V8 produces a reliable 505 bhp all day
long.
When the factory came up with the idea of using a supercharger on the Corvette ZR1, it decided
that the LS7 block was not man enough for the job, and used the 6,162-cc LS3 as starting point
instead. This variant of the legendary small-block V8 has thicker cylinder walls to better withstand the
higher combustion pressures of forced aspiration.
The Geiger engineers, on the other hand, were not only confident the LS7’s cylinder walls could
handle a blower, they felt they could be even thinner, and proceeded to bore out the V8 to a
monstrous 7.6 liters. In the process, they fitted lightweight forged pistons, titanium valve springs and a
more aggressive camshaft. Only then did they strap a pair of turbochargers to custom-made exhaust
manifolds and fit a substantial intercooler down low in the nose.
This heavy-breathing engine required a high-flow air intake system with a big 100-mm throttle
body and a new fuel-injection system with larger pumps. Spent gases exit via a large-diameter
exhaust system with special low-restriction catalytic converters. The final step for the engineers was
to remap the engine computer to suit the new fuel and spark parameters. The result of all their afterhours
hard work was 890 bhp at 6,100 rpm and 694 lbs-ft of torque at 4,500 rpm.
This huge increase in output necessitated a number of other mods. First of all, the extreme heat
generated by the turbos required that a heavily vented hood be fitted. The redesigned nose clip, with
its larger central opening and additional side intakes, directs cooling air to the intercooler and front
brakes. The rear end also incorporates unique Geiger fiberglass bodywork, including a rounded tail
piece with an integrated spoiler and a diffuser panel. In conjunction with the aggressive front splitter,
they are said to reduce aerodynamic lift without increasing drag. The only original bodywork pieces
left on the Z06 Bi-Turbo are the doors and rear-quarter panels.
The Geiger crew next dismantled the Z06’s six-speed manual gearbox and rebuilt it using
reinforced components. They then fitted a race-grade dual-disc clutch, a carbon-fiber propshaft and a
stronger rear differential and halfshafts.
To prepare the chassis for high-speed runs, the engineers swapped the stock suspension for
Geiger’s fully adjustable coil-over kit, which uses a combination of H&R springs and KW dampers
with adjustable spring platforms. The ride height is set 25 mm lower than stock, an important mod