5 Underrated Muscle Cars, Led by a 1-of-164 Buick GS Stage 1 Convertible That Sold $14,400 Under Estimate

RM Sotheby’s sold a triple-black 1970 Buick Gran Sport Stage 1 convertible at its Hershey auction on October 8 for $145,600. The catalog estimate was $160,000 to $200,000, and the car was offered without reserve, so the room set the price.

It came from Michael Leith’s collection, and so did a 1954 Buick Skylark that sold at the same sale for the identical $145,600. A 1987 Grand National from another consignor brought $39,200.

The Buick’s below-estimate result is why it leads this list of underrated muscle cars. Cars nobody fights over tend to be cars nobody documented carefully. Working through Chevrolet’s own dealer information kits and the auction catalogs for the five cars below, we found auction houses disagreeing on how many were built and how big the engine was, and one listing that disagrees with itself on the production total.

1970 Buick GS 455 Stage 1

RM’s catalog rates the 1970 Gran Sport 455 at 350 hp and 510 lb-ft, with the Stage 1 package (a specific Quadrajet tune, bigger valves, a more aggressive cam) raising output to 360 hp. It gives no separate torque figure for the Stage 1. Chevrolet’s September 1969 information kit for the Chevelle, posted by the GM Heritage Center, rates the 454 LS5 at 360 hp and 500 lb-ft. On paper, Buick’s 455 out-torqued Chevrolet’s big-block by 10 lb-ft.

The Hershey car’s rarity claim comes from the Buick Performance Club, which counts it among 164 convertibles built for 1970 with both the Stage 1 and the Turbo-Hydramatic 400. That figure is the club’s, not Buick’s. What the car does carry from Buick is build data from the Sloan Museum archive in Flint, showing it was first invoiced to C.M. Jones, Inc., a dealer in Cuyahoga, Ohio.

Its build included air conditioning, cruise control, a tilt wheel, power windows, a four-way power seat and an AM/FM eight-track, which is a lot of Electra equipment bolted around a 455. Even a clean one doesn’t guarantee a crowd: the 12,000-mile barn-find Gran Sport we covered drew limited bidding.

1969 AMC Hurst SC/Rambler

Mecum sold an A-scheme SC/Rambler at Kissimmee on January 10, 2025, for $56,100. Its listing calls the car “1 of 1,152 produced, with only 379 known to the registry.” When RM Sotheby’s offered one at Auburn in 2017, its catalog called that car one of 1,512 built.

Same four digits, different order; 1,512 is the figure most references use. Neither house names a source for its total, and Mecum doesn’t say which registry counts 379 survivors. RM’s car went unsold against a $55,000 to $65,000 estimate; Mecum’s price eight years later landed inside that range.

The two listings agree on the hardware: an X-code 390 rated at 315 hp, a four-speed with Hurst linkage, and a Twin-Grip differential with 3.54 gears. Mecum adds rear axle torque links, a hood scoop that seals to the carburetor, power front disc brakes and a Sun tach clamped to the steering column. All of that went into AMC’s compact Rambler body.

1970 Chevrolet Monte Carlo SS 454

The GM Heritage Center posts the dealer information kit Chevrolet issued for the 1970 Monte Carlo, dated September 1969 with pages revised in March 1970. The Monte Carlo SS is RPO Z20. The engine table rates the Turbo-Jet 454 (RPO LS5) at 360 hp at 4,400 rpm and 500 lb-ft at 3,200 rpm, the same figures the Chevelle kit of the same date gives the LS5.

The two kits split on the power-team page. The Chevelle kit lists the LS5 with a four-speed. The Monte Carlo kit lists the 454 one way only: Turbo Hydra-Matic and a 3.31 axle. Chevrolet put its biggest engine in its personal-luxury coupe and offered it without a clutch pedal.

The Chevelle kit’s engine-rating page in that September 1969 edition also stops at the LS5. The LS6, the engine that defines the Chevelle SS story, isn’t on it.

Mecum sold a triple-black SS 454 with its build sheet and Protect-O-Plate at Houston on April 5, 2024, for $62,700. The odometer read 84,771 miles.

1984-86 Ford Mustang SVO

Four cylinders will disqualify it for some readers. Ford’s Special Vehicle Operations gave the SVO a turbocharged, intercooled four with an offset hood scoop, a five-speed, four-wheel disc brakes, Koni adjustable front suspension and a bi-plane rear wing. It’s a long way from the Cobra Jet Mustangs Ford built for the drag strip.

RM’s 2016 Auburn catalog describes a 1984 car’s engine as a 175-hp, 2.4-liter SOHC four. Mecum’s 2023 listing for a 1985 says 2.3 liters, which matches Ford’s spec, and that car came with its original window sticker and a Marti Report, which reproduces Ford’s production record for the VIN. If you’re shopping for one, that’s the paperwork to ask for.

RM sold a 1986 SVO at Auburn in 2012 for $7,920 and the 1984 in 2016 for $5,060. Mecum’s 1985, in Medium Canyon Red with 10,820 miles, sold at Harrisburg on July 26, 2023, for $20,900.

1989 Pontiac Turbo Trans Am

Mecum sold a 6,105-mile Turbo Trans Am at Indianapolis on May 15, 2025, for $60,500. The car was still on its Manufacturer’s Statement of Origin. The listing headline says “1 of 1,555 produced.” Further down, the same page says “just 1,550” were built.

Both numbers hold up. Mecum’s text says the 1,555 includes five test cars, and its own breakdown (1,324 T-tops with leather, 187 T-tops with cloth, 24 hardtops with leather, 15 hardtops with cloth) adds to 1,550. RM Sotheby’s catalogs disagree with each other. Its 2012 Auburn catalog called the engine a 3.6-liter and the car one of 1,500. Its John Staluppi Collection catalog says 3.8 liters, 250 hp, and 1,555 cars including the five test units. That car sold for $25,850.

The 3.8 is Buick’s turbocharged, intercooled V6; RM’s Staluppi catalog says it’s the engine used in the GNX, the final version of the Grand National. RM’s 2012 catalog says the Trans Am met the Indianapolis Motor Speedway’s pace car requirements without mechanical modification. Mecum’s listing adds 0-60 mph in 4.6 seconds, a 13.4-second quarter mile and the title of quickest American production car of its year, without naming who ran the test. For a pace car, it was a strange flex: a Pontiac borrowing Buick’s V6, two decades before GM wound the brand down.

Of the five, the Hershey Buick is the only one to clear $100,000. The next-highest result here is the Monte Carlo’s $62,700.

So which belongs on a muscle car list: the four-cylinder SVO and the V6 Turbo Trans Am, or only cars with a V8 and a 1960s or ’70s model year?

Sources: RM Sotheby’s lot catalogs (Hershey 2026, Auburn Fall 2017, Auburn Spring 2012 and 2016, John Staluppi Collection); Mecum lot listings (Kissimmee 2025, Houston 2024, Harrisburg 2023, Indy 2025); Chevrolet 1970 Monte Carlo and Chevelle dealer information kits, GM Heritage Center.

About the Author

Shawn Henry

Administrator

Shawn Henry has spent years writing about cars, and it shows—not in a resume kind of way, but in how he talks about them. He's the type who'll notice the weird trim option nobody remembers and actually know why it mattered. At Backfire News, he covers pretty much the whole spectrum: off-road trucks and trail builds, performance cars, racing, and the collector market. He's comfortable getting into the technical weeds, but he never forgets that most people read about cars because cars are fun, not because they want a spec sheet. His beat runs from classic and collector vehicles to overlanding culture, modified performance builds, new automotive tech, and the industry news that actually affects what ends up in your driveway. Mostly, though, Shawn thinks the best car stories are about people—the builds they pour money into, the road trips, the communities that form around a shared obsession. That's the stuff he likes writing about, and it's what you'll find in his work here.

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