The original 318/904 powertrain was replaced by a locally built 360 with W2 heads and an A-833 four-speed. But problems cropped up with the first engine that replaced the OEM 318. "The first time we fired it up, the lifters were knocking," Shaun recalls. "We went through one cam, and we couldn't figure out why." Flattened lifters were blamed by the engine builder on improper cam break-in, but the problem happened three more times. Diagnosis: Too much valvespring pressure caused by the W2 heads being set up for solid lifters, not hydraulic lifters, thus the spring pressure was too high. That engine was too torn up inside to continue with, so out it came and in went another W2-headed 360, this one built at Geddes Auto Machine in Colorado Springs.
Unfortunately, more problems cropped up again before Shaun took his car to Mopars On The Strip in Las Vegas last year. The 8 3/4-inch rearend-built by the same "expert" who built the Duster's first 360-failed after Shaun drove the car less than one block, setting off a desperate, but successful, nationwide search for another 3.91 ring-and-pinion set, which they installed the day before they loaded the Duster on their trailer and left for Las Vegas.
When the Duster was unloaded and driven to the show field on Saturday of show weekend, the engine started knocking badly. The valve covers were pulled, and the culprit was bent pushrods. They'd come too far to just leave the car at their hotel, so with a little help from their friends, Shaun and his dad pushed it onto the trailer, then back onto the show field on Sunday. They also pushed it into place for this story's photo shoot. The lack of a running engine didn't diminish this Duster's appeal-it earned the Mopar Muscle Best of Show award.
The yet-to-be-functional 360's pushrod problem was traced to faulty rocker arms, then cured once and for all by a complete rebuild by Angelo Vigil at Geddes Auto Machine, who replaced all the bad/broken parts at their expense.
Since then, Shaun's driven and shown his Duster locally, fulfilling his goal of a car built to drive, not one built to be garage art. What's it like to drive? "I would say it's like a bat out of hell," Shaun says of his W2 360-powered Plymouth.
It's also a fine example of a car built with plenty of period-correct '70s-vintage upgrades and with a lot of perseverance to see it through to the finish.
Not only did this '70 Duster...
Not only did this '70 Duster get a set of big-bolt-pattern Rallyes (with custom chrome trim rings) on BFGs; it also got a rebuilt '73 Duster front suspension.
Found on a shelf full of his...
Found on a shelf full of his dad's Mopar parts, Shaun added this ultra-rare original Mopar cassette deck to his Duster. Harm's now has reproductions of the outer housing and mounting brackets.
Fast Facts
'70 Plymouth Duster
Shaun Johnson
Colorado Springs, Co
Mopar Power
- Engine: Chrysler LA-series 360ci V-8, built by Angelo Vigil at Geddes Auto Machine, Colorado Springs, Colorado.
- Engine components include: W2 cylinder heads, Comp Cams High Energy 231/237 (.525 lift) camshaft with Harlan Sharp roller rockers, Weisco forged pistons (10.5 compression), Mopar Performance dual-plane intake manifold with an Edelbrock 750-cfm carburetor, forged steel crankshaft, MSD ignition and tti headers.
- Transmission: A-833 four-speed built by B+M Transmission, Colorado Springs. OEM-style Hurst pistol-grip shifter made by Scott Smith at Harm's Automotive.
- Rearend: Mopar 8 3/4-inch rearend with 3.91 gears and Sure Grip differential.
On the dyno (on pump gas)
- Peak horsepower: 435 @ 5,700 rpm.
- Peak torque: 446lb-ft @ 4,100 rpm.
Sure Grip
- Suspension: OEM-type front torsion bar/rear leaf springs. Original '70 front suspension replaced with '73 Duster front end, rebuilt with Just Suspensions rebuild kit. Monroe gas-adjustable shocks are at all four corners.
- Brakes: What should have been standard on the Duster 340-large-bolt-pattern Mopar discs in front, and big, large-bolt-pattern drums in back.
- Wheels: Custom chrome-plated, large-bolt-pattern Mopar Rallyes. Front: 15x7 inches; rear: 15x8 inches. Tires: BFGoodrich radial TAs all around, 205/60R15 in front, 275/60R15 in back.
High Impact
- Body: What was left of the original '70 Duster unibody was restored by Arthur's Auto Collision and Paint, Colorado Springs. Replacement steel parts sourced from Auto Body Specialties, while Hybrid Fiberglass Solutions made the air cleaner assembly. The scoops on the hood are original Mopar scoops and are functional.
- Paint: GY3 Curious Yella basecoat/clearcoat finish applied by Arthur's Auto Collision and Paint, who accented it with repro black strobe stripes. Timberline Upholstery put on a repro black vinyl top.
- Interior: Hideous looking green plaid bench seats/rubber floor mat were replaced with black '70 Duster deluxe vinyl buckets/rear bench and black carpeting. Repro interior trim sourced from Legendary Auto Interiors and installed by owner.
- Interior also includes: Rallye gauge cluster (rechromed by Mr. G's), Tuff steering wheel, original Mopar AM/FM radio in dash with ultra-rare original Mopar cassette recorder/player and E-Body consolette on transmission tunnel.