Can you build a 426 hemi from a 318 block
Building a 426 Hemi from a 318 block isn’t just a technical challenge—it’s a journey into the world of classic muscle cars, where each engine has its own unique story. The 426 Hemi stands out as an iconic powerhouse in American automotive culture, revered for its high performance and racing pedigree. On the other hand, the 318, often found in Dodge and Plymouth models, has a reputation as a durable and dependable workhorse. But is it really possible to turn a 318 block into a 426 Hemi? Let’s break down what each engine represents, the hurdles you’d face, and practical ways to get Hemi-like performance without the complexities of an engine swap.
Comparing the 426 Hemi and 318 Engines
Before diving into the specifics, let’s get a feel for each engine’s defining characteristics:
| Feature | 426 Hemi Engine | 318 Engine |
|---|---|---|
| Engine Type | V8 with hemispherical combustion chambers | V8 with a standard wedge-head design |
| Displacement | 426 cubic inches (7.0 liters) | 318 cubic inches (5.2 liters) |
| Horsepower | 425 HP (original factory rating) | Around 230 HP (varies by model) |
| Performance | High output, designed for racing | Reliable, general-purpose engine |
| Rarity | Rare and iconic, especially in original form | Common, widely used across Mopar models |
The 426 Hemi is celebrated for its hemispherical combustion chambers, designed to maximize airflow and boost horsepower. While the 318 holds its own as a sturdy and versatile engine, it wasn’t built to achieve the Hemi’s level of performance.
Why Converting a 318 to a 426 Hemi Isn’t Feasible
The idea of transforming a 318 into a 426 Hemi might sound appealing, but the technical differences between them make it nearly impossible. Here’s why:
- Cylinder Head Design
- The Hemi’s hemispherical combustion chambers allow for larger valves and better airflow—design features the 318 lacks. To modify a 318 for Hemi heads would require a major overhaul, including adjusting valve angles and chamber size, which would likely exceed the engine’s structural limits.
- Size and Dimensions
- The 318 simply wasn’t designed with the bore and stroke dimensions of a 426 Hemi. Even if you maxed out the bore size, it wouldn’t match the Hemi’s 4.25-inch bore, and trying to push these limits could damage the block.
- Strength and Durability
- The 318 wasn’t built to handle the power a 426 Hemi can produce. Subjecting it to such forces could risk the engine’s durability and reliability.
- Modification Costs
- Even if the conversion were possible, the extensive re-engineering required would likely cost more than buying a ready-made 426 Hemi crate engine.
Alternative Ways to Get Hemi-Like Performance from a 318
Though a 318-to-426 Hemi conversion is impractical, there are ways to boost the 318’s power and get closer to that Hemi experience.
Option 1: High-Performance 318 Build
- If you want to stick with a 318, investing in performance parts is the most practical route. With quality upgrades, a 318 can achieve impressive horsepower without trying to become a Hemi. Key upgrades include a high-performance camshaft, high-compression pistons, a performance intake, and a carburetor.
| Upgrade | Description | Estimated Cost |
|---|---|---|
| High-performance camshaft | Increases valve lift and airflow | $300-$600 |
| High-compression pistons | Boosts compression for more power | $400-$800 |
| Performance intake | Optimizes fuel-air mix | $250-$500 |
| Performance carburetor | Enhances fuel delivery | $300-$700 |
| Total Approximate Cost | $1250-$2600 |
Option 2: 426 Hemi Crate Engine
- For those who crave the authentic 426 Hemi experience, a crate engine offers a straightforward solution. Though expensive, a crate engine provides a complete, fully tested Hemi with guaranteed performance.
Option 3: Stroker Kit for the 318
- A stroker kit increases the 318’s displacement, allowing it to deliver more torque and horsepower. This approach can bring the 318 closer to a larger engine’s performance while retaining the original block.
| Option | Engine Outcome | Average Cost |
|---|---|---|
| Crate Engine | Authentic 426 Hemi with iconic power | $18,000-$25,000 |
| Stroker Kit | 390+ cubic inches of power from a 318 | $1,500-$3,000 (plus labor) |
Embracing the Hemi Legacy
The 426 Hemi is more than an engine; it’s a piece of automotive history. Its groundbreaking design, developed for high-performance racing, has made it a legend on and off the racetrack. Chrysler’s engineering mastery with the Hemi changed the muscle car scene forever, making the 426 Hemi a symbol of Mopar’s legacy. The 318, though more humble in design, remains a cornerstone of Mopar’s lineup, respected for its reliability and adaptability. Attempting to transform a 318 into a 426 Hemi isn’t realistic, but by understanding and appreciating each engine’s unique strengths, car enthusiasts can find ways to achieve impressive performance without compromising the legacy of either.
Also Read: How Virtual Chassis Fabric Works
Conclusion
Attempting to turn a 318 block into a 426 Hemi engine is technically and financially impractical due to significant design differences. However, with a few strategic upgrades, the 318 can be enhanced to deliver impressive power, especially when coupled with performance parts and a stroker kit. Alternatively, for those set on the authentic Hemi experience, purchasing a crate engine is the best path. Embracing each engine’s strengths allows enthusiasts to enjoy the best of both worlds: the Hemi’s raw power and the 318’s versatility.
The 318 might not reach the power of a 426 Hemi, but it can still be the heart of a powerful, customized ride that stays true to its heritage.