Not coincidentally, the 2007 Shelby GT500 sports
the largest displacement engine installed in a volume version of
the Mustang since 1973.
The 1995 SVT Mustang Cobra R used a 5.8-liter
300 horsepower overhead valve V-8, and 250 units were produced.
The 2000 SVT Mustang Cobra R used a 385 horsepower 5.4-liter dual
overhead cam V-8, and a limited run of 300 cars were produced.
While the big block, overhead cams and four
valves per cylinder contribute significantly to the 475-horsepower
output of the 2007 Shelby GT500’s 5.4-liter V-8, a Roots-type
supercharger and intercooler are the icing on the cake. In fact,
the configuration is similar to the Ford GT supercar, offering the
right combination of classic Ford big-block power and modern technology.
Using the Ford GT as a blueprint, SVT has given the GT500 more total
horsepower than any factory Mustang in the car’s celebrated
"The Shelby GT500 delivers on the essence
of two great names in Ford performance – a mix of SVT’s
modern-day experience with supercharging and the Shelby GT500’s
heritage of big-block power," says Jay O’Connell, SVT
chief vehicle engineer.
Full certification testing is not yet complete.
However, Hau Thai-Tang, director, Advanced Product Creation and
Special Vehicle Team, says achieving 475 horsepower is no problem.
"We have great confidence that the 2007 Shelby GT500 will produce
at least 475 horsepower -- perhaps more. And that would be right
in line with the original GT500 experience. It, too, under promised
and over delivered."
With the stout cast-iron, 5.4-liter Triton V-8
engine as a starting point, the Shelby GT500 adds a Roots-type 8.5-pounds-per-square-inch
Eaton supercharger and water-to-air intercooler producing 475-horsepower.
"A screw-type supercharger that we use
in the Ford GT gives you a little more top end, and the Roots type
is a little fatter in the midrange," says O’Connell.
Given that the GT500 will be used as a daily driver far more than
the Ford GT is, it’s the ideal choice."
Adding forced-induction power is more than just
a bolt-on proposition. The engine’s internals need upgrading
for the sake of strength and durability. To that end, the Shelby
GT500’s powerplant benefits from unique connecting rods and
forged pistons to handle the extra strain on the lower end of the
"The entire induction system is unique,"
says O’Connell. "That includes the intake, intercooler,
fuel supply – everything."
The all-new intake manifold helps to channel
the supercharged fuel-air mixture into the cylinders. The low-profile
manifold design also effectively packages the entire induction system
under the GT500’s special air-extractor hood. Fuel comes from
a dual-bore electronic throttle body borrowed from Ford’s
6.8-liter V-10 truck engine program.
Beating the Heat
To manage heat produced by 475 horses, engineers
devised a set of GT500 specific features, including an air-extractor
hood, a high-capacity aluminum radiator, an intercooler mounted
below the blower, a loop-style power-steering cooler and an oil-to-water
stacked-dish engine oil cooler.
4-Valve Heads from Ford GT
While supercharging is a key element in the
Shelby GT500’s ability to generate so much horsepower, another
major contributing component is the design of cast-aluminum, four-valve
cylinder heads sourced from the Ford GT supercar.
Machining changes are incorporated into the
outside ends of the heads and to the left rear cam cap to fit the
engine into the Mustang chassis.
Developed specifically for supercharged applications,
these high-performance heads use high-flow ports and specially calibrated
dual-overhead camshafts to deliver optimum engine "breathing"
along with surprisingly good fuel efficiency and emissions.
The cams and valvetrain are specific to the
Shelby GT500. The cam drive system is unique and designed to fit
into the Mustang engine compartment, which is narrower than the
Ford GT’s. The oil pan and windage tray are the wet-sump setup
from the Mustang GT. The Ford GT uses a dry-sump arrangement.
Powered by SVT
To enthusiasts, the real beauty of any performance
car rests with its engine. That idea certainly wasn’t lost
on Carroll Shelby because Mustangs that bore his name have traditionally
brought his unique sense of style and personality directly into
the engine compartment. One Shelby signature feature – special
finned-valve covers embossed with "COBRA Powered By Ford"
– soon became the envy of so many Ford V-8 owners.
The GT500 is equipped with special "Powered
by SVT" finned-cam covers to hint at the beauty of all those
horses lurking in the engine below. Mated to the Ford GT 4-valve
cylinder heads are unique exhaust manifolds that help to better
scavenge spent gases out of the cylinders and into the custom-tuned
mufflers and dual-exhaust system.
And the aggressive exhaust note, which is unobtrusive
in everyday driving situations, was truly custom tuned.
"More than 40 different muffler tunings
were tested, measured and evaluated to come up with the right sound,"
says William Woebkenberg, an engineer with SVT.
A special device called a "tuned exhaust
crossover" was incorporated to create the special sound. Unlike
the H-pipe design used by the Mustang GT, the Shelby GT500 uses
an X-shape stamping to create the desired sound and increase power
output through dynamic scavenging.
The gearbox used by the 2007 Shelby GT500 also
is a rarity. Few transmissions exist in the marketplace today that
can handle the torque loads generated by the supercharged GT500,
so engineers are opting to stick with the proven heavy-duty performance
of the TR6060 6-speed manual gearbox.
The GT500 employs an upgraded version of the
T-56, which first appeared in the 2000 SVT Mustang Cobra R, powered
by a naturally aspirated 5.4-liter V-8 with 385 horsepower, and
later in the supercharged 2003 SVT Mustang Cobra whose DOHC 4.6-liter
produced 390 horses. For the Shelby GT500, the six-speed manual
will be geared to make the most of the supercharged 5.4-liter’s
broad power band.
"One of SVT’s goals in creating a
vehicle is to deliver a balance of performance – acceleration,
cornering, braking," says director Thai-Tang.
Another goal is to develop products and processes
that can be applied not just to high-performance products, but also
to other vehicles and in other parts of the company.
Then and Now
Performance cars have evolved dramatically since their heyday in
the 1960s. In terms of safety, efficiency and refinement, today’s
street machines totally outperform their elder muscle car colleagues
in nearly all categories. Yet the story is seldom told about the
tremendous gains made in reducing emissions while increasing overall
The fact is, the GT500 is easily twice as powerful
as the hottest V-8 package offered when Mustang was first introduced
– yet still produces from 100 to 300 times fewer emissions.
Additionally, today’s modern "MOD" V-8 powertrain
enjoys a nearly 60-percent increase in average fuel economy compared
to corresponding Ford products produced 30 years ago.
Back in the so-called Muscle Car era, driving
a street beast with more than 400 horsepower was a dicey proposition.
When dual carburetors, progressive linkage and dual-point ignitions
were part of the equation, performance came with a price –
drivability. Running too lean or too rich – or with the timing
or spark out of adjustment could mean it would misfire or "carbon
up" – sometimes with thick, black smoke coming from the
tailpipe. Worse yet was fuel economy, with most of the big, high-powered
V-8s at the time netting anywhere from six to 10 miles per gallon
in typical driving.
Ford’s "MOD" V-8 family of engines
makes more power than any Ford motors of the past, yet tops 20 mpg
on the highway and meet the government’s LEV-II tailpipe emissions
Multi-valve Engine Technology
Modern, race-derived technology provides an interesting power comparison:
The GT500 with a 5.4-liter, DOHC, supercharged V-8 produces better
than 100 horsepower more with nearly 100 fewer cubic inches. Compare
that with the 1967 Shelby GT500’s 355-horsepower, 428-cubic-inch-displacement,
The GT500 uses cylinder heads with four valves
per cylinder and double overhead cams for optimum engine "breathing."
Using multiple valves per cylinder provides the engine with a more
efficient airflow, generating higher peak horsepower. As an additional
benefit, multi-valve engines better utilize the air-and-fuel mixture
in the cylinders with less waste and unburned fuel vapor. Also,
multi-valve engines are better suited to help scavenge exhaust gases
out of the cylinder after combustion is complete for more power
with cleaner tailpipe emissions.
In addition, supercharging produces the peak
horsepower of a much larger-displacement, naturally aspirated engine.
Yet, at lower throttle applications, the smaller displacement enabled
by supercharging consumes less fuel, resulting in increased fuel
economy and lower emissions.
As a result, the 2007 Shelby GT500 is designed
not only to be the most powerful Mustang from the factory –
but also one of the cleanest.