The DeSoto Firesweep I Convertible, powered by a 5.7-liter V8 engine producing 280 horsepower, represented a significant offering in the American automotive landscape of 1957 and 1958. Positioned as a premium offering within the DeSoto lineup, the Firesweep aimed to blend style, performance, and comfort. It was built upon DeSoto’s full-size platform, sharing its basic architecture with Chrysler and Imperial models, but distinguished by its unique styling and trim. The Firesweep Convertible, in particular, embodied the optimism and exuberance of the late 1950s, offering an open-air driving experience with a touch of luxury. Production spanned only two model years, contributing to its relative rarity and collectibility today.
Technical Specifications
| Brand | DeSoto |
| Model | Firesweep |
| Generation | Firesweep I Convertible |
| Type (Engine) | 5.7 V8 (280 Hp) |
| 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 | 280 Hp @ 4600 rpm |
| Power per litre | 48.8 Hp/l |
| Torque | 515 Nm @ 2400 rpm / 379.84 lb.-ft. @ 2400 rpm |
| Engine displacement | 5735 cm3 / 349.97 cu. in. |
| Number of cylinders | 8 |
| Engine configuration | V-engine |
| Cylinder Bore | 103.12 mm / 4.06 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 | 76 l / 20.08 US gal | 16.72 UK gal |
| Length | 5499 mm / 216.5 in. |
| Width | 1989 mm / 78.31 in. |
| Height | 1443 mm / 56.81 in. |
| Wheelbase | 3099 mm / 122.01 in. |
| Front track | 1547 mm / 60.91 in. |
| Rear (Back) track | 1516 mm / 59.69 in. |
| Front overhang | 940 mm / 37.01 in. |
| Rear overhang | 1461 mm / 57.52 in. |
| Ride height (ground clearance) | 142 mm / 5.59 in. |
| Minimum turning circle (turning diameter) | 14.2 m / 46.59 ft. |
| Approach angle | 16.5° |
| Departure angle | 11.4° |
| Ramp-over (brakeover) angle | 10.5° |
| Drivetrain Architecture | The Internal combustion engine (ICE) drives the rear wheels of the vehicle. |
| Drive wheel | Rear wheel drive |
| Number of gears and type of gearbox | 3 gears, manual transmission |
| Front suspension | Independent coil spring |
| Rear suspension | Leaf spring |
| Front brakes | Drum, 279 mm |
| Rear brakes | Drum, 279 mm |
| Steering type | Worm-reduction unit |
Powertrain & Engine Architecture
The heart of the 1957-1958 Firesweep Convertible was DeSoto’s 5.7-liter (349.97 cubic inch) V8 engine. This engine, designated as the “A-series” block, featured a cast iron block and aluminum cylinder heads. It utilized a conventional overhead valve (OHV) valvetrain with two valves per cylinder. Fuel delivery was managed by a Carter carburetor, a common setup for the era. The 10:1 compression ratio contributed to the engine’s respectable 280 horsepower output at 4600 rpm and 379.84 lb-ft of torque at 2400 rpm. The engine’s robust bottom end and relatively simple design made it durable, though not particularly sophisticated by modern standards. The standard transmission was a three-speed manual, providing a direct connection to the rear wheels. While an automatic transmission was available on other Firesweep models, the convertible was primarily offered with the manual gearbox.
Driving Characteristics
The Firesweep Convertible with the 5.7L V8 and three-speed manual transmission offered a driving experience typical of large American cars of the late 1950s. Acceleration was brisk, but not overwhelming, with the engine delivering strong torque throughout the rev range. The three-speed manual gearbox, while providing driver control, wasn’t known for its precision or quick shifts. The car’s substantial weight (approximately 3,800 pounds) and relatively soft suspension tuning prioritized ride comfort over sporty handling. Steering was accomplished via a worm-reduction unit, which provided ample assistance but lacked the direct feel of more modern steering systems. Overall, the driving experience was geared towards relaxed cruising and showcasing the car’s stylish design.
Equipment & Trim Levels
The Firesweep Convertible was positioned as a relatively well-equipped vehicle. Standard features included full wheel covers, whitewall tires, a deluxe steering wheel, and a generously sized bench seat upholstered in cloth and vinyl. Power steering and power brakes were optional extras, as were a radio, heater, and various trim enhancements. The interior featured a dashboard with a prominent instrument cluster, showcasing the speedometer, fuel gauge, and other essential indicators. The convertible top was manually operated, and a tonneau cover was available as an accessory. The Firesweep Convertible’s interior was designed to provide a comfortable and stylish environment for both driver and passengers.
Chassis & Braking
The Firesweep Convertible utilized a body-on-frame construction, common for American cars of the period. The chassis featured an independent coil spring suspension at the front, providing a relatively smooth ride. The rear suspension employed a traditional leaf spring setup, which was robust but less refined than the front suspension. Braking duties were handled by drum brakes on all four wheels, measuring 279mm in diameter. While adequate for the car’s weight and performance, the drum brakes lacked the stopping power and fade resistance of disc brakes. Steering was accomplished via a worm-reduction unit, offering ample assistance but limited feedback.
Market Reception & Comparison
The DeSoto Firesweep Convertible was generally well-received by automotive critics, who praised its stylish design and comfortable ride. However, it faced stiff competition from other American convertibles, including offerings from Ford, Chevrolet, and Plymouth. Compared to its siblings within the DeSoto lineup, the Firesweep Convertible represented the top-of-the-line offering, boasting a more luxurious interior and a more powerful engine than the lower-trim models. Fuel economy was typical for the era, averaging around 15-18 miles per gallon. Reliability was generally good, although the carburetor could require occasional adjustments.
Legacy
The DeSoto Firesweep Convertible, despite its short production run, has become a sought-after collectible among enthusiasts of classic American automobiles. The 5.7-liter V8 engine, while not particularly high-tech, proved to be durable and relatively easy to maintain. Today, well-preserved examples command significant prices in the collector car market. The Firesweep Convertible represents a bygone era of American automotive design, characterized by bold styling, generous proportions, and a focus on comfort and luxury. Its rarity and historical significance ensure its continued appeal to collectors and enthusiasts for years to come.
