318 vs 273: Is it Worth the Swap?

For classic Mopar enthusiasts, the quest for more power and improved performance is a constant pursuit. When looking at early Mopar V8s, the 273 cubic inch engine often comes up as a capable, albeit sometimes overlooked, powerplant. However, many are curious about whether upgrading to a slightly larger displacement, specifically the 318 cubic inch V8, offers a significant advantage. This article will delve into the details of both engines, compare their specifications, and discuss the potential benefits and considerations of making the switch from a 273 to a 318.

Understanding the 273 Cubic Inch V8

The Plymouth/Dodge 273 V8 was introduced in 1964 and was a popular choice for a range of Mopar vehicles, from compacts like the Valiant and Barracuda to larger models. It was Mopar's first small-block V8. While not the most powerful engine in the Mopar arsenal, it was a well-engineered and reliable unit. Early versions featured a two-barrel carburettor, producing around 180 horsepower, while the more potent Commando 273 featured a four-barrel carburettor and produced closer to 235 horsepower. It was known for its good low-end torque and relatively good fuel economy for its era.

Introducing the 318 Cubic Inch V8

The 318 V8, a member of the Chrysler LA (Lightweight A) engine family, debuted in 1967. It quickly became one of Chrysler's most produced and versatile engines, powering everything from full-size sedans to trucks and muscle cars. The 318 is essentially an enlarged version of the 273, sharing many common design elements. This shared architecture can make the swap more straightforward for those familiar with Mopar V8s. The 318 typically produced more horsepower and torque than its 273 predecessor, with figures generally ranging from 230 to 270 horsepower depending on the year and specific configuration (two-barrel or four-barrel carburettor).

Key Differences and Advantages of the 318

The primary difference between the 273 and the 318 lies in their displacement. The 318 boasts an additional 45 cubic inches, which translates directly into a potential for more power and torque. This increased displacement allows the 318 to breathe more efficiently and generate greater combustion pressure. Here's a breakdown of the key advantages:

• Increased Torque: The larger bore and stroke of the 318 provide a significant boost in low-end and mid-range torque. This means better acceleration off the line and more responsive cruising.
• Higher Horsepower Potential: While stock figures are often comparable or slightly higher for the 318, its larger displacement offers a better foundation for performance modifications.
• Parts Availability: The 318 was produced in much larger numbers than the 273. This means that finding spare parts, rebuild kits, and performance upgrades for the 318 is generally easier and often more affordable.
• Engine Family Commonality: The 318 shares many components and design principles with other LA series engines, such as the 340 and 360. This can make sourcing compatible parts for engine swaps or upgrades simpler.

Technical Specifications Comparison

To better illustrate the differences, let's compare some typical specifications:

As you can see from the table, the 318 generally offers a more substantial power and torque output, primarily due to its increased displacement. The bore and stroke figures highlight how the 318 achieves this larger capacity.

Is the 318 a Good Upgrade Over the 273?

Yes, in most cases, a 318 is considered a good upgrade over a 273. The increase in displacement directly translates to a noticeable improvement in performance, particularly in terms of torque and acceleration. If you're looking for a more potent and responsive driving experience from your Mopar classic, the 318 is a very sensible choice. The relative ease of swapping as they share many physical dimensions and mounting points further enhances its appeal.

Larry Taylor's comment highlights a crucial point for any engine work: ensuring the fuel system is clean. If your car has been sitting for a while, draining old fuel is essential before attempting to start the engine, regardless of whether it's the original 273 or a swapped 318. Old fuel can degrade and cause significant issues, potentially leading to engine damage.

Considerations for a 273 to 318 Swap

While the 318 is a solid upgrade, there are a few things to consider:

• Engine Mounts: While the LA engine family is generally compatible, ensure the specific engine mounts for your vehicle are correct for the 318.
• Exhaust Manifolds/Headers: The exhaust port spacing might differ slightly, so you may need different manifolds or headers.
• Transmission Compatibility: Most transmissions that were bolted to a 273 will also bolt to a 318, as they share the same bellhousing bolt pattern. However, consider if your current transmission is robust enough to handle the increased power and torque of the 318.
• Cooling System: A slightly larger engine might generate more heat, so ensure your cooling system (radiator, fan) is in good condition or consider an upgrade if you plan on heavy use or performance modifications.
• Fuel System: As mentioned, ensure your fuel tank and lines are clean. You might also consider a more robust fuel pump if you're pushing the 318 for more power.
• Carburettor and Ignition: While the stock carburettor from a 273 Commando might work, a carburettor and ignition system specifically tuned for a 318 will yield better results.
• Weight: The 318 is slightly heavier than the 273 due to its larger block, but the difference is usually not significant enough to drastically alter vehicle handling characteristics for most street applications.

Performance Potential and Modifications

The 318 is a fantastic platform for mild to moderate performance enhancements. Common upgrades include:

• Four-barrel carburettor: Swapping a two-barrel for a four-barrel, along with a corresponding intake manifold, will significantly boost performance.
• Performance camshaft: A camshaft with a more aggressive profile can dramatically improve power output.
• Headers: Aftermarket headers can improve exhaust flow, leading to more power.
• Ignition upgrades: Electronic ignition systems offer more reliable and consistent spark.

These modifications, when applied to a 318, can easily push its power output well beyond that of even the most potent 273 Commando.

Frequently Asked Questions

Q1: Is the 318 a direct bolt-in replacement for a 273?
While many components are shared, it's not always a completely direct bolt-in. You'll need to verify engine mounts, exhaust connections, and potentially ancillary components. However, it's generally considered one of the easier V8 swaps within the Mopar family.

Q2: Will my transmission bolt up to a 318?
Yes, the bellhousing bolt pattern for the 273 and 318 is the same, so your transmission should bolt up. However, consider the transmission's suitability for the increased power.

Q3: Is the 318 more fuel-efficient than the 273?
Due to its larger displacement, the 318 will likely consume slightly more fuel than a comparable 273 under similar driving conditions. However, the power increase often makes it feel more efficient, as you'll need to press the accelerator less to achieve desired speeds.

Q4: What year 318 is best?
For most enthusiasts, later model 318s (from the 1980s onwards) often featured improvements like more efficient heads and potentially better fuel delivery systems, even in carbureted form. However, early 318s are also excellent and perfectly suitable.

Q5: Are parts for the 318 readily available?
Absolutely. The 318 was produced in vast quantities, making parts readily available through classic car suppliers, auto parts stores, and online retailers.

Conclusion

In summary, upgrading from a 273 to a 318 cubic inch V8 in your Mopar classic is a highly recommended and beneficial modification. The increase in displacement brings with it more torque, more horsepower, and a more engaging driving experience. Coupled with the excellent parts availability and the relative ease of the swap, the 318 stands out as a superb choice for those seeking to enhance the performance of their Mopar vehicle. Just remember to heed the advice about ensuring your fuel system is clean and ready for its new heart!

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