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Background of the Chevrolet C-70 Platform
The Chevrolet C-70 was part of GM’s medium-duty truck lineup from the 1960s through the early 1990s. Designed for vocational use—dump trucks, grain haulers, and utility rigs—the C-70 featured a robust ladder frame, split rear axle, and a variety of engine options. In 1978, many units came equipped with the 350 small block V8, a reliable but torque-limited engine for heavy hauling. GM also offered big block options like the 366 and 427, which were popular in fleet and farm applications due to their low-end grunt and durability under load.
Why Swap to a Big Block
The original 350 small block in one such C-70 had worn cam lobes and was showing signs of fatigue. Rather than rebuild the small block, the owner opted to transplant a rebuilt 454 big block from a one-ton truck. The 454, known for its torque-rich performance and external balance configuration, offered a significant upgrade in hauling capability—especially for gravel and fill work on rural terrain.
Mounting Challenges and Frame Compatibility
The 350 used a cradle-style front engine mount, common in GM’s medium-duty trucks. The question arose whether this mount could be reused or repositioned for the longer 454 block. Field experience and salvage yard insights suggest that the frame crossmember on C-60 to C-75 trucks from 1973 to 1987 is often pre-drilled for both small and big block configurations. This means the cradle can typically be relocated forward to accommodate the longer block, or replaced with a mount from a donor truck.
Flywheel and Balance Considerations
GM produced three externally balanced engines: the 292 inline-six, the 400 small block, and the 454 big block. When swapping in a 454, it’s critical to use a flywheel designed for that engine. Using a flywheel from a 350 or 366 can cause severe vibration due to imbalance. One workaround is a balance plate—a spacer that compensates for the weight difference between crank and flywheel. These are available from performance suppliers and cost under $20. However, for best results, a proper 454 flywheel should be sourced.
Crankshaft Swaps and Displacement Tweaks
Some builders opt to swap the crankshaft from a 400 big block into a 454 block to create a 427. This hybrid approach was popular in the 1980s among hotrodders and farm mechanics alike. It requires careful attention to bearing clearances and piston compatibility but can yield a high-torque engine with improved balance characteristics.
Exhaust and Cooling System Adjustments
Swapping a big block into a C-70 also requires changes to the exhaust system. The 454’s wider heads and taller deck height mean that manifolds or headers from the small block won’t fit. Custom or donor exhaust components must be sourced. Additionally, a four-core radiator is recommended to handle the increased thermal load, especially during summer hauling.
Real-World Anecdotes and Lessons Learned
One operator recalled installing a 454 into a ¾-ton pickup that originally had a 292 inline-six. With only minor changes to motor mounts and cooling, the swap was successful. However, a friend who swapped a 427 into a 454-equipped truck without changing the flywheel experienced severe vibration at 1,500 RPM—nearly shaking the truck apart. Once the correct flywheel was installed, the issue disappeared.
Another user suggested that before committing to a full engine swap, consider installing an RV cam into the existing 350. This upgrade can dramatically improve torque and drivability, especially when paired with free-flowing mufflers. For some applications, this may be a more cost-effective solution.
Recommendations for a Successful Swap
Swapping a 454 big block into a Chevrolet C-70 dump truck is a practical upgrade for farm use, offering improved torque and hauling capacity. With careful attention to mounting, balance, and cooling, the conversion can extend the truck’s service life and performance. Whether hauling gravel or navigating muddy fields, the big block breathes new life into a classic workhorse.
The Chevrolet C-70 was part of GM’s medium-duty truck lineup from the 1960s through the early 1990s. Designed for vocational use—dump trucks, grain haulers, and utility rigs—the C-70 featured a robust ladder frame, split rear axle, and a variety of engine options. In 1978, many units came equipped with the 350 small block V8, a reliable but torque-limited engine for heavy hauling. GM also offered big block options like the 366 and 427, which were popular in fleet and farm applications due to their low-end grunt and durability under load.
Why Swap to a Big Block
The original 350 small block in one such C-70 had worn cam lobes and was showing signs of fatigue. Rather than rebuild the small block, the owner opted to transplant a rebuilt 454 big block from a one-ton truck. The 454, known for its torque-rich performance and external balance configuration, offered a significant upgrade in hauling capability—especially for gravel and fill work on rural terrain.
Mounting Challenges and Frame Compatibility
The 350 used a cradle-style front engine mount, common in GM’s medium-duty trucks. The question arose whether this mount could be reused or repositioned for the longer 454 block. Field experience and salvage yard insights suggest that the frame crossmember on C-60 to C-75 trucks from 1973 to 1987 is often pre-drilled for both small and big block configurations. This means the cradle can typically be relocated forward to accommodate the longer block, or replaced with a mount from a donor truck.
Flywheel and Balance Considerations
GM produced three externally balanced engines: the 292 inline-six, the 400 small block, and the 454 big block. When swapping in a 454, it’s critical to use a flywheel designed for that engine. Using a flywheel from a 350 or 366 can cause severe vibration due to imbalance. One workaround is a balance plate—a spacer that compensates for the weight difference between crank and flywheel. These are available from performance suppliers and cost under $20. However, for best results, a proper 454 flywheel should be sourced.
Crankshaft Swaps and Displacement Tweaks
Some builders opt to swap the crankshaft from a 400 big block into a 454 block to create a 427. This hybrid approach was popular in the 1980s among hotrodders and farm mechanics alike. It requires careful attention to bearing clearances and piston compatibility but can yield a high-torque engine with improved balance characteristics.
Exhaust and Cooling System Adjustments
Swapping a big block into a C-70 also requires changes to the exhaust system. The 454’s wider heads and taller deck height mean that manifolds or headers from the small block won’t fit. Custom or donor exhaust components must be sourced. Additionally, a four-core radiator is recommended to handle the increased thermal load, especially during summer hauling.
Real-World Anecdotes and Lessons Learned
One operator recalled installing a 454 into a ¾-ton pickup that originally had a 292 inline-six. With only minor changes to motor mounts and cooling, the swap was successful. However, a friend who swapped a 427 into a 454-equipped truck without changing the flywheel experienced severe vibration at 1,500 RPM—nearly shaking the truck apart. Once the correct flywheel was installed, the issue disappeared.
Another user suggested that before committing to a full engine swap, consider installing an RV cam into the existing 350. This upgrade can dramatically improve torque and drivability, especially when paired with free-flowing mufflers. For some applications, this may be a more cost-effective solution.
Recommendations for a Successful Swap
- Verify engine mount compatibility and frame drilling before installation.
- Use a flywheel specifically balanced for the 454.
- Upgrade to a four-core radiator and ensure proper fan shroud clearance.
- Modify the exhaust system to fit big block dimensions.
- Inspect transmission input shaft and clutch compatibility.
- Consider a balance plate only if a proper flywheel cannot be sourced.
Swapping a 454 big block into a Chevrolet C-70 dump truck is a practical upgrade for farm use, offering improved torque and hauling capacity. With careful attention to mounting, balance, and cooling, the conversion can extend the truck’s service life and performance. Whether hauling gravel or navigating muddy fields, the big block breathes new life into a classic workhorse.
