This 1983 Cadillac DeVille Has an LS Swap, Coilovers, and Even a Stick Shift

Sep 26, 2023

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Pro-touring cars have been following the same formula for many years now: lower the center of gravity, tune the suspension geometry and spring rates, install big brakes, and utilize some type of modern V-8 and manual transmission. These methods have been applied to many types of cars, but when it comes to application types, most people gravitate to GM's F-body platform, or perhaps a Ford Mustang. But Matt Graves isn't most people. He has an affinity for obscure builds, and his 1983 Cadillac Coupe DeVille is the ultimate example of a funny idea that morphed into a real thing. "Pro luxury," as he calls it, is the concept of building a pro-touring car out of a full-size luxury coupe or sedan.

Lowering a big Cadillac isn't exactly a groundbreaking new trend, but when you add in grippy rubber on all four corners, huge disc brakes, 600 horsepower, and a stick shift, things get pretty wild. Thanks to many bench-racing sessions and some internet propaganda, Matt stayed motivated to keep chipping away at this project and the "Chicken Coupe" rolled out of his Greenback, Tennessee, garage in 2021, and onto the highways of the HOT ROD Power Tour. Let's dig a little deeper to find out how he pulled it off.

For starters, Matt is marketing manager at American Powertrain in Cookeville, Tennessee, a company that offers five- and six-speed transmissions and installation kits for many types of vehicles. Matt sees thousands of great builds in his travels and he's in tune with the latest trends in the pro-touring market, but following trends isn't the goal with pro luxury. Matt's intentions started with a rolling chassis that he'd bought several years ago. He determined it was too far gone and was on the brink of giving up on the concept altogether when friends and pro luxury supporters Jeff Lee, Marcus Heurich, Jefferson Bryant, and Jon Clark pooled their money together to buy this 1983 Cadillac Coupe DeVille as a surprise gift to springboard the project. It was a rolling chassis with a decent interior and paint; a blank canvas for Matt and his friends.

Underneath, the Cadillac shares many components with GM's B-body platform (Impala/Caprice), though it does have a different wheelbase and a few other small variances. The good news is that aftermarket suspension components for an Impala bolt directly to the Cadillac frame. This realization led to the use of a QA1 Stage 2 B-body suspension system, which features tubular control arms and double-adjustable coil-overs on all four corners, as well as hefty front and rear anti-sway bars. Baer Brakes got the call when it was time to implement a big brake kit, and Matt went with 14-inch rotors and six-piston calipers for the ultimate stopping power. He also installed a Baer ReMaster master cylinder, proportioning valve, and brake lines.

Tim King was a major help with the suspension and brakes, and Gary Garner of Garner Automotive dialed in the suspension alignment before the big Caddy hit the road. Rolling stock consists of American Racing VN510 Draft wheels, which measure 18x10 inches and feature staggered tire fitment, with 255/40R18 up front and 275/40R18 out back. The Kumho Ecsta PS91 tires provide great grip on the highway and autocross course.

The Chicken Coupe is powered by a 427ci LS engine from World Products. The car features their cast-iron block, packed with an Eagle crankshaft with 4.250 inches of stroke. The Manley connecting rods and Mahle pistons are a bulletproof combination, and the World Products 220cc cylinder heads move air very efficiently. A Comp Cams roller camshaft features a split duration of 248/254 degrees and lift of 0.637/0.657 inch, and it's supported by Comp valvesprings and pushrods. Keith Jesse at Holley advised Matt on the fuel-injection system, which starts with a Holley EFI split race intake manifold with multiport fuel injectors and 1,000-cfm throttle body. The original-style fuel tank features the company's EFI in-tank fuel pump, with the whole EFI operation running their Terminator X system, tuned by Dr. EFI.

MSD LS coils light the fire, and a set of Hooker long-tube headers (for a G-body) sends fumes into a custom 3-inch exhaust system with Borla mufflers. The World Products 427 cranks out 600 horsepower and runs on 93-octane pump gas. The engine wears gold paint and Holley's Pontiac-style LS valve covers, part of a plan for the Chicken Coupe. You'll also notice plenty of satin-black treatments underhood, including the Holley accessory drive system. A Frostbite aluminum radiator and dual electric fan setup (for an A-body) keeps the 7.0-liter LS engine cool. Andrew Erichsen stepped in to help with wiring, as the car features an Painless Performance system tied into the Terminator X engine management.

Back in the day, Cadillac wasn't afraid to push the envelope when planning engine displacement. By the 1980s, however, the 500ci monster that powered millions of Cadillacs left the chat, in favor of more fuel-efficient engines. Cadillac was the first American manufacturer to introduce cylinder deactivation for mass-production cars. That engine, known as the "V8-6-4" didn't prove as successful as was hoped, and the subsequent HT 4100 engine was only slightly better. The "High Technology" 4.1-liter V-8 engine had an aluminum block and cast-iron cylinder heads, which is inherently a bad combination. It cranked out only 135 horsepower, touting a digital fuel-injection system that offered an advertised fuel economy of 20 miles per gallon. Matt's new powerplant rivals the car's original fuel economy while making nearly five times the horsepower.

Behind the engine is where it gets fun, as this may be the world's only stick-shift Coupe deVille. As an advocate of manual transmissions, Matt made this a mandatory item on the to-do list. After all, he and Robert Hall are the brains behind American Powertrain's "Save the Stick" marketing campaign that's still going strong today. He started the transmission conversion by adapting a set of G-body pedals to the Cadillac.

Will Baty at Centerforce helped set up the clutch with a DYAD twin-disc system inside a Quick Time bellhousing. Behind that is a Tremec Magnum six-speed modified by American Powertrain, complete with a custom Lokar shifter and boot that fits snugly against the plush split-bench seats. Moving farther back, a custom American Powertrain driveshaft is mated to a Currie 9-inch rearend, which has been narrowed one inch on each side and fitted with an Eaton Truetrac differential, 31-spline axles, and 3.73 gears. The Chicken Coupe tips the scales at 4,085 pounds, which is actually lighter than a modern CTS-V, surprisingly.

The body is relatively stock, aside from the vented hood and subtle use of decals, but the interior does have a few special features. Instead of the original gauge cluster, Matt used a Holley EFI dash, which fits nicely and goes well with the woodgrain. Additional customizations of the dash include a new control panel to go along with the Vintage Air GEN IV Magnum A/C system, and a Kenwood CD player feeding a series of Kicker speakers. The finishing touch, and possibly one of Matt's favorite items on the car, is the gold Trans Am-style steering wheel, a beautiful piece from Lecarra.

Matt said this build wouldn't have been possible without help from so many great friends in the automotive industry, from acquisition of the rolling chassis to help and building advice. Matt received plenty of emotional support along the way from friends like Wayne Henry and Scott Hicks, who also helped wrench, and, of course, ongoing support from his wife, Kellie.

Since its completion in 2021, Matt has driven the car on the HOT ROD Power Tour and taken it on a few spirited rides across the Tail of the Dragon, a famous mountain road near his home in east Tennessee. He's not afraid to push the car's limits, and he's always excited to keep moving forward on the project. Future upgrades include a repaint with a Bandit Trans Am theme, complete with hood graphics (that might help explain some of the Pontiac and Trans Am components throughout the car). For now, he's enjoying the weathered paint and plush interior, and shocking onlookers with his intensely unique Cadillac.

Photos by Tommy Lee Byrd

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