Ameer Randolph
Swapping a fuel tank in a vehicle is a complex process that requires careful planning and execution. In the case of a Cummins swap, there are several factors to consider. One user on the Cummins Forum seeks advice on how to approach the fuel system when swapping a 2nd gen 12v Cummins engine into a 1980 C20 squarebody, specifically whether modifications to the stock sending units would be viable. Another user shares their experience of using the stock fuel tank with no modifications in a similar swap, but highlights the challenge of dual tanks due to the need for a return fuel line for each tank. Engine mounts, suspension, and frame modifications are also critical aspects of a Cummins swap, as the weight and torque of the Cummins engine differ significantly from the original equipment.
| Characteristics | Values |
|---|---|
| Fuel system | Low-pressure fuel supply is sent to the P-pump via a single filter Platinum series FASS system |
| Fuel tank | Stock fuel tank with no modifications; dual tanks would require a return fuel line for each tank |
| Fuel supply pressure | 45 psi |
| Fuel gauge | 130-mph second-generation Camaro speedometer |
| Engine | 12-valve Cummins engine |
| Engine weight | 1200 lbs |
| Transmission | Six-speed NV5600 |
| Transfer case | NP241 |
| Suspension | Atlas spring, 2000 lbs with 4" lift |
| Axles | Front: Dodge Dana 60; Rear: Dana 80 |
| Axle gearing | 4.10 |
| Chassis | 3/4-ton |
| Towing capacity | Up to 20,000 lbs |
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What You'll Learn
Fuel system modifications
One common question is whether to retain the stock fuel tank or opt for modifications. Some people have used the stock fuel tank with no modifications when swapping a 12v Cummins engine. However, dual tanks can be more complex, as each tank requires a separate return fuel line. In such cases, a larger fuel tank, such as a Blazer fuel tank with a capacity of 32 to 34 gallons, can simplify the setup.
For those retaining the stock sending units, modifications may include removing the sock at the bottom of the unit and eliminating any gas filters, running them directly into the lift pump. It is also important to consider the fuel lines, as the stock fuel lines may need to be cut and replaced with diesel-rated fuel hoses. The return fuel line may also need to change size before returning to the stock return.
Additionally, the Cummins engine's increased torque can impact the fuel system. It is recommended to build custom engine mounts to handle the higher torque, as the original mounts may not be sufficient.
The availability of resources and the willingness to spend money, time, and effort will influence the fuel system modifications. Diesel Cummins engines are known for their ease of modification, and various adapter kits and aftermarket parts are available to facilitate the process.
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Engine mounts
Several options are available for engine mounts in the Cummins swap. One option is to build your own engine mounts. This option is advised by some as the off-the-shelf engine mounts from many companies use the original 1st-gen Dodge mounts, which are similar to the rubber biscuit mounts in the SB 383 and will not withstand the Cummins engine's torque. The recommended alternative is to find a set of 2nd-gen Dodge mounts with big round rubber bushings and a cast iron core. These mounts will better handle the vibrations from the Cummins engine.
Another option is to purchase an engine mount conversion kit. BoCID offers a Motor Mount Conversion Swap Kit for the Chevy Suburban 6BT Cummins Engine for model years 1973-1987. This kit is constructed from high-strength steel and features a corrosion-resistant coating. It is designed for ease of use, with no welding, cutting, or drilling required.
Additionally, G Force offers engine drop crossmembers for 4WD models, which are said to make installation easier without sacrificing quality.
Some users have also mentioned using the Tennessee Diesel Power crossmember and motor mount kit, which is said to hold up well.
When installing a Cummins 6BT into a Chevy square body, a conversion motor mount is required to ensure proper placement of the engine relative to the OEM frame mount isolators. These mounts are manufactured from laser-cut structural steel and precision welded to handle the stress and torque of the high-powered drivetrain. They fit both 2WD and 4WD models, and no body or suspension lift is required.
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Transmission options
There are several transmission options available for a Cummins swap. One option is to choose between a reliable five or six-speed manual transmission or a heavy-duty automatic transmission. Examples of manual transmissions that can be mated to Cummins blocks include the NV4500 five-speed, G56, ZF6, or NV5600 6-speed. For automatic transmissions, options such as the 47RH, 47RE, 48RE, 68RFE, Ford 5R110, 6R140, or an Allison can be used without any problem.
Another factor to consider when choosing a transmission is the adapter plate required. For example, Destroked offers an adapter plate that allows for a Cummins engine to be paired with a 4R100 transmission. CA Conversions also offers a complete kit to bolt a five or six-speed Allison transmission to any Cummins engine.
Additionally, the donor vehicle or engine can impact the transmission choice. For instance, a 12-valve Cummins engine may require different transmissions depending on the donor vehicle.
It is also important to consider the cost implications of different transmission options. The cost of a Cummins swap can vary depending on the chosen transmission and other factors. For example, a standalone transmission controller and torque converter may be required when retaining a factory Ford 5R110 TorqShift transmission.
Furthermore, the availability of parts and the complexity of the installation can influence the chosen transmission. For instance, opting for a manual transmission with a mechanically injected 6BT 12-valve 5.9L Cummins engine can limit the number of electronic hurdles and provide rock-solid reliability.
In summary, when considering transmission options for a Cummins swap, it is important to take into account factors such as performance requirements, budget, donor vehicle or engine, cost, availability of parts, and installation complexity to make an informed decision.
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Frame reinforcement
To address this, Rob Bonney Fabrication (RBF) offers steering box outer reinforcement plates for 1973-1987 Chevy K-series trucks. These reinforcement plates provide additional support to the steering box area, preventing potential failure under the increased stress of the Cummins engine.
Additionally, RBF offers frame boxing plates for GM K Series Trucks and Suburbans built between 1967 and 1987. Boxing the frame involves adding steel plates to the inside of the frame rails, connecting the two sides and creating a boxed structure. This significantly increases the rigidity and strength of the frame, improving its ability to handle the additional torque and power of the Cummins engine.
For those planning to run higher power outputs, it is common to box the frame rails, at least across the front axle spring hangers. This provides extra reinforcement to handle the increased stress and torque. It is recommended to use quality tools and equipment, such as a good welder, to ensure a proper and durable installation.
Furthermore, when performing a Cummins swap, it is advisable to build your own engine mounts. The stock engine mounts may not be able to withstand the increased torque of the Cummins engine. By creating custom mounts, you can ensure they are up to the task and reduce vibrations.
Finally, reinforcing the steering box itself is another important consideration. As mentioned earlier, removing the steering box for reinforcement can be a time-consuming task, but it will be worth the effort for improved durability and performance.
In summary, frame reinforcement is crucial when performing a Cummins engine swap in a square-body Chevy. By using reinforcement plates, boxing the frame rails, building custom engine mounts, and reinforcing the steering box, you can ensure the truck's frame can handle the increased stress, torque, and power of the Cummins engine.
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Fuel supply pressure
Maintaining a minimum fuel supply pressure is essential for the VP44's operation, lubrication, and cooling. A lack of sufficient fuel pressure can lead to overheating of the VP44, reducing its lifespan. It is recommended to have at least 5 psi of fuel supply pressure from the lift pump to ensure the VP44 functions correctly.
The choice of lift pump is crucial in achieving the desired fuel supply pressure. Some Cummins owners opt for the OE piston lift pump, which provides higher flow rates. Others prefer the self-priming, electric Carter lift pump, which was standard on the 5.9L ISB Cummins in Rams. However, due to its mounting location on the engine block, it is susceptible to vibration, impacting its longevity. Aftermarket options, such as the Power Driven Diesel's Predator lift pump, offer advantages like being belt-driven and fully mechanical, increasing fuel supply pressure with higher engine speeds.
When performing a Cummins swap, particular attention must be given to the fuel lines and supply pressure. The supply line carries fuel from the tank to the lift pump, while the return line sends excess fuel back to the tank. It is recommended to use steel brake lines and rubber fuel hoses with double clamps to ensure a secure seal. Additionally, a Wix 33270 inline filter on the supply side helps keep the fuel clean.
Maintaining the correct fuel supply pressure is essential for the overall health of the engine. Running a fuel pressure gauge is advisable to monitor the lift pump's performance and identify any potential issues. By keeping an eye on fuel supply pressure, owners can ensure the engine receives the necessary fuel volume and prevent overheating, promoting the longevity of the Cummins engine.
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Frequently asked questions
Cummins swap refers to the process of installing a Cummins engine into a vehicle that did not originally have one, such as an old Chevy or a GMC.
For a fuel system, you can either modify the stock sending units or use a different fuel tank. If you want to retain the stock features such as two tanks and gauges, you may need to remove the sock and gas filters from the stock sending units. Alternatively, you could use a Blazer fuel tank, which is simpler as it only requires running lines from the sending unit to the lift pump.
There are a few transmission options available for a Cummins swap. You can choose between reliable five or six-speed manual transmissions or heavy-duty automatic transmissions. For manual transmissions, options include the NV4500 five-speed, G56, ZF6, or NV5600 6-speed. For automatic transmissions, you can use a 47RH, 47RE, 48RE, 68RFE, Ford 5R110, 6R140, or an Allison.
Here are some tips for a successful Cummins swap:
- Build your own engine mounts as the stock mounts may not withstand the torque of the Cummins engine.
- Use a custom-built Atlas spring for better suspension.
- Ensure a minimum of 2"-4" lift to clear the oil pan on the front axle.
- Use second-generation Dodge mounts to reduce vibrations.
- Consider using frame boxing plates designed for trucks receiving Cummins swaps.
A Cummins swap can provide increased power and torque, improved reliability, and better fuel efficiency. It can also result in a stylish and durable rig that can tow heavy loads. Additionally, Cummins engines are known for their torque, which is ideal for a truck motor.
