The DeSoto Firedome III Convertible, specifically the facelifted 1958 model, represented a pinnacle of American automotive styling and engineering during the late 1950s. Produced for a relatively short period, from 1957 to 1958, it was positioned as DeSoto’s premium offering, competing with other luxury convertibles from Buick, Oldsmobile, and Chrysler. The 1958 facelift brought significant cosmetic changes, including revised grillework, tailfins, and trim, aiming to capture the burgeoning enthusiasm for bolder, more futuristic designs. This particular variant, equipped with the 5.9-liter V8 engine and TorqueFlite automatic transmission, was a key component of the Firedome lineup, offering a blend of performance and convenience for the discerning American driver.
Technical Specifications
| Brand | DeSoto |
| Model | Firedome |
| Generation | Firedome III Convertible (facelift 1958) |
| Type (Engine) | 5.9 V8 (295 Hp) TorqueFlite |
| Start of production | 1957 |
| End of production | 1958 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Cabriolet |
| Seats | 6 |
| Doors | 2 |
| Fuel Type | Petrol (Gasoline) |
| Power | 295 Hp @ 4600 rpm |
| Power per litre | 49.9 Hp/l |
| Torque | 529 Nm @ 2400 rpm / 390.17 lb.-ft. @ 2400 rpm |
| Engine displacement | 5916 cm3 / 361.02 cu. in. |
| Number of cylinders | 8 |
| Engine configuration | V-engine |
| Cylinder Bore | 104.65 mm / 4.12 in. |
| Piston Stroke | 85.85 mm / 3.38 in. |
| Compression ratio | 10:1 |
| Number of valves per cylinder | 2 |
| Fuel injection system | Carburettor |
| Engine aspiration | Naturally aspirated engine |
| Valvetrain | OHV |
| Engine oil capacity | 3.8 l / 4.02 US qt | 3.34 UK qt |
| Coolant | 16.1 l / 17.01 US qt | 14.17 UK qt |
| Fuel tank capacity | 87 l / 22.98 US gal | 19.14 UK gal |
| Length | 5552 mm / 218.58 in. |
| Width | 1989 mm / 78.31 in. |
| Height | 1450 mm / 57.09 in. |
| Wheelbase | 3200 mm / 125.98 in. |
| Front track | 1549 mm / 60.98 in. |
| Rear track | 1516 mm / 59.69 in. |
| Front overhang | 892 mm / 35.12 in. |
| Rear overhang | 1461 mm / 57.52 in. |
| Ride height (ground clearance) | 140 mm / 5.51 in. |
| Minimum turning circle | 15.1 m / 49.54 ft. |
| Approach angle | 16.3° |
| Departure angle | 11.6° |
| Ramp-over angle | 10° |
| Drivetrain Architecture | Rear wheel drive |
| Number of gears and type of gearbox | 3 gears, automatic transmission TorqueFlite |
| Front suspension | Independent coil spring |
| Rear suspension | Leaf spring |
| Front brakes | Drum, 305 mm |
| Rear brakes | Drum, 305 mm |
| Steering type | Worm-reduction unit |
Powertrain & Engine Architecture
The heart of the 1958 DeSoto Firedome III Convertible was the 5.9-liter (361 cubic inch) V8 engine. This engine, designated within the Chrysler family as the “RB” series, was a robust and relatively modern design for its time. It featured a cast iron block and cylinder heads, with a 10:1 compression ratio. The engine utilized a single Carter carburetor, providing fuel delivery to the overhead valve (OHV) configuration. The valvetrain employed hydraulic lifters, reducing the need for frequent maintenance. Paired with this engine was the Chrysler TorqueFlite three-speed automatic transmission. This transmission was known for its smoothness and durability, and it was a popular option for luxury cars of the era. The TorqueFlite featured a torque converter, providing a smooth launch and efficient power transfer.
Driving Characteristics
The combination of the 295 horsepower V8 and the TorqueFlite automatic transmission delivered a comfortable and capable driving experience. While not a sports car, the Firedome III Convertible offered ample power for highway cruising and passing maneuvers. The automatic transmission, while smooth, did result in some power loss compared to the available manual transmission options. The gear ratios were optimized for relaxed cruising, with a focus on providing effortless acceleration rather than outright speed. The car’s substantial weight (approximately 4,000 pounds) meant that it wasn’t particularly nimble, but the independent front suspension helped to provide a reasonably comfortable ride.
Equipment & Trim Levels
As DeSoto’s flagship convertible, the Firedome III was well-equipped. Standard features included power steering, power brakes, a deluxe steering wheel, full wheel covers, and a generously sized bench seat upholstered in premium cloth or vinyl. The interior featured a distinctive instrument panel with a combination of analog gauges and warning lights. Optional extras included air conditioning, a radio, power windows, and a continental kit. The 1958 facelift brought revised interior trim options, with more vibrant color schemes and updated fabric patterns.
Chassis & Braking
The Firedome III Convertible rode on a sturdy body-on-frame chassis. The front suspension utilized independent coil springs, providing a more comfortable ride compared to the solid axle setups found on some competing models. The rear suspension employed leaf springs, which were durable and capable of handling the car’s weight. Braking was accomplished via drum brakes on all four wheels. While adequate for the time, the drum brakes lacked the stopping power of modern disc brake systems. The steering system utilized a worm-reduction unit, which provided relatively heavy but precise steering feel.
Market Reception & Comparison
The 1958 DeSoto Firedome III Convertible was generally well-received by automotive critics. It was praised for its stylish design, comfortable ride, and powerful engine. However, some critics noted that the car was relatively expensive compared to its competitors. Compared to other Firedome variants, the V8/TorqueFlite combination offered a more refined and convenient driving experience, appealing to buyers who prioritized comfort over outright performance. The 1.8L and smaller engine options were aimed at a more budget-conscious buyer. Fuel economy, unsurprisingly, was not a strong point, averaging around 12-15 miles per gallon.
Legacy
The DeSoto marque was discontinued in 1961, making the Firedome III Convertible a relatively rare and collectible classic car today. The 5.9-liter V8 engine, while not known for being particularly fuel-efficient, proved to be durable and reliable when properly maintained. Parts availability can be a challenge, but a dedicated community of DeSoto enthusiasts helps to keep these cars on the road. The 1958 Firedome III Convertible represents a significant piece of American automotive history, embodying the optimism and extravagance of the late 1950s. Well-preserved examples command significant prices in the collector car market, appealing to those who appreciate classic American design and engineering.
