Ford 391FT Engine: Legacy, Specifications, and Modern Equivalents

[MikePhua]

The Ford 391FT engine, a member of Ford's FT series, was a heavy-duty V8 engine produced from the mid-1960s through the late 1970s. It was primarily used in medium-duty trucks, such as the F-700 and F-800, and was known for its low-end torque and durability. As these engines age and become harder to maintain, owners often seek modern equivalents or replacements that match the original's performance and reliability.

Engine Specifications

• Displacement: 391 cubic inches (6.4 liters)
  
• Configuration: V8, Overhead Valve (OHV)
  
• Bore x Stroke: 4.05" x 3.78" (103 mm x 96 mm)
  
• Compression Ratio: Approximately 7.6:1
  
• Horsepower: Approximately 235 hp at 4,000 rpm
  
• Torque: Approximately 372 lb-ft at 2,000 rpm
  
• Fuel System: Carbureted, typically a 2-barrel carburetor
  
• Cooling System: Water-cooled with a conventional radiator setup
  

These specifications highlight the engine's design focus on low-end torque, making it suitable for heavy-duty applications requiring substantial pulling power at lower speeds.

Modern Equivalents and Replacement Options
When considering a replacement for the 391FT, it's essential to match the engine's characteristics, such as torque output and physical dimensions. Some potential modern equivalents include:

• Ford 6.8L V10: While not a direct replacement, the 6.8L V10 offers a similar torque curve and can be adapted for medium-duty truck applications. However, modifications may be necessary to fit the existing engine bay and transmission.
  
• Ford 6.2L V8: This engine provides a balance between power and fuel efficiency. It's commonly found in newer Ford Super Duty trucks and could serve as a potential replacement with appropriate adaptations.
  
• Cummins ISB 6.7L: For those seeking a diesel option, the Cummins ISB 6.7L engine offers robust torque characteristics and is widely used in medium-duty applications. However, fitting this engine may require significant modifications.
  

It's important to consult with a professional mechanic or engine specialist to determine the best replacement option based on specific requirements and vehicle compatibility.

Challenges in Replacement
Replacing the 391FT engine presents several challenges:

• Physical Dimensions: The 391FT has specific dimensions that may not align with modern engine bays, necessitating modifications.
  
• Transmission Compatibility: The existing transmission may not be compatible with newer engines, requiring adapter plates or complete replacement.
  
• Mounting Points: Engine mounts designed for the 391FT may not align with modern engines, necessitating custom fabrication.
  
• Electrical and Fuel Systems: Newer engines may require updated electrical wiring and fuel systems to function correctly.
  

Addressing these challenges requires careful planning and consultation with professionals experienced in engine swaps.

Preserving the 391FT
For those wishing to retain the original 391FT engine, regular maintenance is crucial:

• Routine Oil Changes: Regular oil changes help maintain engine lubrication and prevent premature wear.
  
• Cooling System Maintenance: Ensure the radiator and cooling system components are functioning correctly to prevent overheating.
  
• Fuel System Checks: Regularly inspect the carburetor and fuel lines for leaks or blockages.
  
• Electrical System Inspection: Check the ignition system, including the distributor and spark plugs, for optimal performance.
  

By adhering to a strict maintenance schedule, the longevity of the 391FT engine can be extended, preserving its historical value and functionality.

Conclusion
The Ford 391FT engine holds a significant place in the history of Ford's heavy-duty truck offerings. While modern replacements are available, they come with their own set of challenges. Whether opting for a replacement or preserving the original engine, it's essential to consider the specific requirements and consult with professionals to ensure the best outcome.