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TECH NOTES
Who: Scott Davis
What: 1972 Plymouth Duster
Where: Concord, NC
Exterior: Scott says Laura is the artist
and he’s the “welder/grinder.” Between
the original Dart and the new Duster,
the pair has developed a talent for
metalworking. Using 16-gauge steel
from Tractor Supply, they beat and
banged replacement sheetmetal into
the troubled rust spots—namely, the
lower quarter-panels and trunklid. The
car must have sat with the rear hang-
ing out from under an awning. A trunk-
mounted fuel cell meant no need for a
gas door, so they patched up a new
panel. “The Duster doesn’t have many
body lines, but the lines it does have
are very intentional. The hardest part
was getting that curve just right,” Laura
said. The stripes imitate that of a
’Cuda, and were never on a new
Duster: “Yeah, that pisses off the pur-
ists,” Scott said, laughing. He picked up
stripes specially designed for a Duster
on eBay Motors. A local body shop
gave them tips and the confidence to
paint the car themselves. Waiting for a
sunny day, they used a two-stage
gloss-black paint and shot it in the
gravel driveway beside the house. They
finished it by wet-sanding and buffing
it with 3M Finesse-it polish.Right: The difficulty with
building any Mopar on a
budget is avoiding the hard-to-
find parts specific to a Mopar.
According to owner Scott
Davis, the 440 headers from
Schumacher are the most
expensive part on the car. To
Scott’s knowledge, there is
only one other 440ci-powered
Mopar competing in
autocross. A 6-inch K&N filter
sits on top, sucking air through
a functional hoodscoop.Engine: The 440ci features a 0.030-
overbore with a forged crank, stock
rods, and Speed Pro forged pistons
with 10:5:1 final compression (the
same as some 440 Six Pack engines).
That drivetrain was passed to the
Duster, built initially by HP Engineers of
Norwood, NC. A Comp Cams hydraulic
flat-tappet cam features a 0.509-inch
lift, 292-/299-degree advertised dura-
tion, and 108 degrees lobe separation.
Edelbrock E-Street 75cc heads top the
short-block, along with an Edelbrock
Air Gap intake with a two-barrel carb
adapter plate. The secret sauce to the
build is the Holley 500-cfm Ultra XP
two-barrel carburetor. The Ultra is an
updated version of the 4412 two-barrel
designed for circle-track racing, often
found on cars in NASCAR Late Model
Divisions. The electronics in the Duster
are minimal, with a Holley electric fuel
pump, MSD 6AL ignition box, and MSD
Blaster II coil. Schumacher Tri-Y headers
with 3-inch collectors dump into dual
3-inch exhaust and Summit Racing
mufflers, which exit before the rear axle.
Drivetrain: The Mopar 727 TorqueFlite
transmission has served Scott and team
well, topped with a Hurst Slap Shifter.
The original 8^3 ⁄ 4 rear with 3:90 gears
still resides under the Duster. It assem-
bles like a Ford 9-inch with a replaceable
centersection, and Scott is currentlyworking on building another rear-axle
assembly to swap out at the track.
Wheels & Tires: It’s essential to have a
big tire footprint in autocross. The
Duster sits on American Muscle Bullitt
Anthracite wheels measuring 18x10 all
around with a 25mm backspacing.
They’re wrapped in BFGoodrich Rival S
315/30R18. That’s big rubber. For refer-
ence, Dodge Challenger Widebodies
come with 305mm-wide tires. Scott had
to trim the inside lip of the fenders to
get them to clear, with minimal rubbing.
Suspension: The Duster is dropped
2 inches all around with QA1 double-
adjustable shocks. Up front, QA1
tubular upper control arms are accom-
panied by stock lower control arms,
which Scott boxed in for added
strength. The budget build retains the
original leaf-spring rear setup with
additional springs to stiffen it up. It also
has one of the largest torsion bars on
the market from Performance Suspen-
sion Technology. The custom front
sway bar measures 22 mm and is
designed for the rear of a race car.
The team added it to the front with
some modification. Scott said this was
necessary, as the heavy big-block was
hard to find a big enough sway bar. The
latest upgrade was the new Borgeson
quick-ratio box, which required some
trimming on the steering column, but it
helped cut down on the rotation of the
steering wheel and increased accuracy.
Brakes: Scott installed Wilwood’s
forged Dynalite brake kit with a Classic
Performance master cylinder. A brake
booster wouldn’t clear the big-block, so
the brakes are manual. The brakes and
suspension use the original spindles.Left: The all-aluminum Hard-Core Gray 500-
cfm Ultra XP carburetor is Scott’s secret for
autocross racing. The short straightaways
only allow a quick moment for secondaries
to kick in before immediately getting on
the brakes, which unsettles the car. It still
has 500 cfm and features 20 percent more
fuel capacity than the previous generation,
meaning there’s plenty of fuel feeding the
big-block.
Below: The interior is basic, with Jegs-brand
racing seats and no radio—simple and
perfect for autocrossing, as some rulebooks
require a street interior. The rollcage was
installed in Scott’s garage.50 CAR CRAFT OCTOBER 2019