The DeSoto Firesweep I Convertible, powered by a 5.7-liter V8 engine and TorqueFlite automatic transmission, represented a significant offering in the American luxury car market during its brief production run from 1957 to 1958. Positioned as a stylish and comfortable convertible, it aimed to capture a segment of buyers seeking a blend of performance and open-air enjoyment. The Firesweep was part of the first generation of the Firesweep line, built on DeSoto’s full-size platform, and was intended to compete with offerings from Buick and Oldsmobile. This particular configuration, the 280 horsepower V8 paired with the TorqueFlite, was a mid-range offering within the Firesweep lineup, offering a balance between power and ease of driving.
Technical Specifications
| Brand | DeSoto |
| Model | Firesweep |
| Generation | Firesweep I Convertible |
| Type (Engine) | 5.7 V8 (280 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 | 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 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 | 14.2 m / 46.59 ft. |
| Approach angle | 16.5° |
| Departure angle | 11.4° |
| Ramp-over angle | 10.5° |
| 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, 279 mm |
| Rear brakes | Drum, 279 mm |
| Steering type | Worm-reduction unit |
Powertrain & Engine Architecture
The heart of the Firesweep I Convertible was DeSoto’s 5.7-liter (349.97 cubic inch) V8 engine. This engine, designated within the Chrysler corporation as the “Hemi” despite not being a true hemispherical head design, featured a cast iron block and aluminum cylinder heads. It utilized a single Carter carburetor for fuel delivery and employed an overhead valve (OHV) valvetrain. The 280 horsepower output was achieved at 4600 rpm, while peak torque of 515 Nm (379.84 lb-ft) arrived at 2400 rpm. This configuration provided a good balance of power for cruising and acceleration. The engine’s 10:1 compression ratio was typical for the era. The TorqueFlite automatic transmission, a three-speed unit, was a Chrysler product known for its smoothness and durability. It was a fully automatic transmission, offering a selector for Park, Neutral, Reverse, and Drive.
Driving Characteristics
The 1957-1958 Firesweep I Convertible with the 5.7L V8 and TorqueFlite offered a comfortable and relatively powerful driving experience for its time. While not a sports car, the 280 horsepower engine provided ample power for highway cruising and passing maneuvers. The TorqueFlite transmission contributed to smooth gear changes, making for a relaxed driving experience. Compared to the base engine options available in other DeSoto models, this V8 offered a noticeable performance upgrade. However, it wasn’t as potent as the larger displacement engines found in some competing models from Buick or Oldsmobile. The automatic transmission, while convenient, did result in some power loss compared to a manual transmission, and the gear ratios were optimized for cruising rather than aggressive acceleration.
Equipment & Trim Levels
The Firesweep I Convertible was generally well-equipped for the late 1950s. Standard features included full wheel covers, whitewall tires, a deluxe steering wheel, and a padded dashboard. Interior upholstery was typically cloth and vinyl, with a wide range of color options available. Power steering and power brakes were often included as standard equipment, enhancing the driving experience. Optional extras included a continental kit, power windows, a radio, and air conditioning. The convertible top was power-operated, adding to the convenience. The interior trim was designed to convey a sense of luxury, with bright trim accents and comfortable seating.
Chassis & Braking
The Firesweep I Convertible utilized a body-on-frame construction, typical of American cars of the era. The chassis featured an independent coil spring suspension in the front, providing a comfortable ride. The rear suspension employed leaf springs, which were more robust and suitable for handling the car’s weight. Braking was accomplished via drum brakes on all four wheels, measuring 279mm in diameter. While adequate for the time, the drum brakes lacked the stopping power of modern disc brake systems. Steering was handled by a worm-reduction unit, which provided relatively easy steering effort but lacked the precision of more modern steering systems.
Market Reception & Comparison
The DeSoto Firesweep I Convertible received mixed reviews from automotive critics. While praised for its styling and comfortable ride, it was often criticized for its lack of performance compared to some of its competitors. The 5.7L V8 and TorqueFlite combination was considered a good all-around choice, but some reviewers felt it lacked the punch of larger engines. Fuel economy, typical for a large American car of the 1950s, was relatively poor. Reliability was generally good, but maintenance costs could be high due to the complexity of the engine and transmission. Compared to other DeSoto models, the Firesweep I Convertible was positioned as a premium offering, appealing to buyers who wanted a stylish and comfortable convertible.
Legacy
The DeSoto Firesweep I Convertible, while only produced for two years, remains a desirable classic car today. The 5.7L V8 and TorqueFlite powertrain, when properly maintained, is known for its durability. However, finding parts for these older engines and transmissions can be challenging and expensive. The Firesweep I Convertible is appreciated by collectors for its distinctive styling and its representation of the American automotive design aesthetic of the late 1950s. Values for well-preserved examples have been steadily increasing in recent years, reflecting the growing interest in classic American cars. The TorqueFlite transmission, in particular, is regarded as a robust and reliable unit, contributing to the long-term appeal of this vehicle.
