The Resurgent Mopar 340: A UK Buyer's Guide

The Mopar 340 engine holds a legendary status amongst automotive enthusiasts, a true icon of American muscle that perfectly blended performance with streetability. For decades, its distinctive rumble and potent output have captured the hearts of drivers across the globe, and here in the UK, its appeal is just as strong. Whether you're planning a full restoration, a custom build, or simply looking to inject some serious grunt into your classic, the enduring allure of the 340 remains undeniable. This comprehensive guide will navigate you through the process of acquiring a Mopar 340 engine or its components, from sourcing complete crate engines to exploring high-performance stroker kits and understanding the intricacies of the modern replacement block. Prepare to delve into the heart of a true automotive legend and discover how you can bring its power to your garage.

The Enduring Legacy of the Mopar 340

First introduced in late 1967 for the 1968 models, the Mopar 340 was more than just a slightly larger sibling to the 318 cubic inch engine. It was purpose-built for performance, a statement of intent from the engineers at Mopar. Right from its inception, it was equipped with a suite of performance-oriented features designed to give it a significant edge. These included a robust dual-row timing chain, a vital windage tray to improve oil control at high RPMs, generously sized 2.02-inch intake and 1.60-inch exhaust valves for superior airflow, and a high-rise dual-plane intake manifold topped with an AVS carburettor. Furthermore, it boasted a strong steel crankshaft and high-performance cylinder heads, all contributing to its formidable reputation. The 340 was unequivocally here to make a statement, and it certainly did.

Throughout its production life, the 340 saw various refinements and changes. While some might not be considered purely performance-driven, they reflect the evolving automotive landscape. For instance, a cast-iron crankshaft was introduced from 1973 onwards. The induction systems also varied significantly, ranging from an 850-cfm Thermoquad to the legendary Six Pack (or Six Barrel for Plymouth aficionados), all resting proudly atop its "high performance" heads. This continuous evolution ensured the 340 remained relevant and potent for its era, cementing its place in the annals of muscle car history.

Sourcing Your Mopar 340 Engine and Components

For enthusiasts looking to get their hands on a Mopar 340, the good news is that this iconic engine hasn't been relegated solely to the realm of vintage finds and meticulous rebuilds. Mopar itself has recognised the enduring demand and has brought back an all-new 340, allowing you to acquire a factory-fresh engine that honours its heritage.

Complete Crate Engines: The Mopar 340 Six Pack

Remarkably, you can now purchase an all-new 340 Six Pack engine directly from Mopar. This is a significant offering for anyone seeking modern reliability paired with classic performance. This new iteration does its formidable heritage proud. While the venerable 1970 340, in its Six Pack livery, boasted around 290 horsepower, the new 340 Six Pack is rated by Mopar to achieve 330 hp and 330 lb/ft of torque. As we'll delve into later, independent testing has often shown these ratings to be conservative, revealing even greater potential.

When considering a complete crate engine, you benefit from a meticulously assembled unit, often with modern manufacturing tolerances and material improvements. This can save countless hours of sourcing individual components and ensure a reliable foundation for your project. Be sure to check with authorised Mopar Performance dealers, both locally and internationally, for availability and shipping to the UK.

Unleashing More Power: Mopar 340-416 Stroker Kits

For those who crave even more displacement and power from their 340, a stroker kit is an incredibly popular and effective upgrade. A stroker kit essentially increases the engine's stroke, thereby increasing its overall cubic inches and, consequently, its torque and horsepower potential. If you're looking to transform your 340 into a formidable 416 cubic inch beast, dedicated suppliers are available.

One prominent source for these high-performance kits is CNC-Motorsports, which offers an extensive selection of Mopar 340-416 stroker kits. They cater to a wide range of applications, from street-focused kits designed for pump gas with suitable pistons, to wild, fully forged rotating assembly kits engineered to meet the rigorous demands of racing. When investing in a stroker kit, the quality of components is paramount. CNC-Motorsports, for example, offers kits featuring parts from leading name brands in the performance world, ensuring durability and power. These include:

• Eagle
• Scat
• Callies
• K1
• JE/SRP
• Diamond
• Wiseco
• Mahle CP
• Keith Black

These brands are renowned for their high-quality crankshafts, connecting rods, and pistons, all crucial for a reliable and powerful stroker build. When selecting a kit, consider your intended use – street, strip, or both – to choose the appropriate compression ratio, piston material (cast, hypereutectic, or forged), and rod design.

Deep Dive into the Mopar 340 Replacement Block (PN P5007552AB)

The cornerstone of any serious Mopar 340 build, whether it's a restoration or a high-performance project, is a solid block. Mopar Performance offers an all-new replacement block, part number P5007552AB, which serves as an excellent foundation. This block carries the original 340 production casting part number but with an 'M' appended, clearly identifying it as a Mopar Performance component.

While it boasts a few cosmetic differences from the original 340 block, it has been meticulously machined to ensure compatibility with all standard 340 production components, making it a versatile choice for builders. However, it's the internal enhancements that truly set this replacement block apart:

• High Nickel Content: Unlike some thin-wall castings, this block features a high nickel content, significantly enhancing its strength and durability. This is crucial for high-stress applications and longevity.
• Four-Bolt Main Bearing Caps: The centre three main bearing journals are equipped with four-bolt main caps. This dramatically improves crankshaft stability and reduces flex, especially beneficial in high-horsepower applications.
• Standard 340 Journal Size: It maintains the original 340 journal size, ensuring compatibility with existing or readily available crankshafts and bearings.
• Thicker Webbing and Pan Rail: Similar to the robust 340 T/A blocks, this replacement block features thicker webbing and pan rails, adding rigidity and further strengthening the engine's lower end.
• Thicker Deck Surface: A thicker deck surface provides enhanced cylinder head sealing and reduces the likelihood of cylinder head distortion under extreme conditions.
• Thicker-Bore Cylinder Walls: The cylinder walls are thickened in the major/minor thrust directions, offering greater stability and reducing bore distortion, which contributes to better ring seal and power.
• Deck Height: The approximate deck height is 9.600 inches, providing a consistent and accurate starting point for engine builders.

It's important to note a few specific requirements and recommendations for this block:

• It requires the use of Mopar PN 05281090BA oil filter, or an equivalent.
• It is not recommended for use with roller tappets, indicating its design is optimised for flat tappet camshafts.
• Builders may find it requires the use of a late '70s 318 motor mount on the left side for proper fitment in some applications.

These details highlight that while it's a modern block, it's designed to honour and integrate with the original 340's architecture, providing a robust and reliable foundation for your build.

The Heart of the Beast: Internal Components of the New Mopar 340 Six Pack

Beyond the robust block, the new Mopar 340 Six Pack crate engine features a carefully selected array of internal components designed for a balance of durability and performance.

• Crankshaft: The engine utilises an internally balanced cast crankshaft, adhering to the 340's original 3.31-inch stroke. While a cast piece, its internal balancing contributes to smoother operation and reduced vibration.
• Connecting Rods: Forged I-beam connecting rods are employed, offering superior strength compared to cast rods, essential for handling the engine's power output.
• Pistons: The engine currently uses cast pistons. While these are perfectly adequate for the rated horsepower, many high-performance builders might consider upgrading to forged pistons for ultimate durability, especially if pushing the engine beyond its stock ratings or adding forced induction. This would be our primary wish for an improvement.
• Compression Ratio: The short-block assembly results in a compression ratio of 10.0:1. This is a well-chosen ratio that strikes an excellent balance between performance and practicality, making it entirely suitable for use with readily available Premium pump fuel from your local petrol station.

Top End Performance: Heads, Cam, and Induction

The top end of the new Mopar 340 Six Pack is equally impressive, featuring components that enhance its breathing and overall power delivery.

• Cylinder Heads: Sitting atop the short-block is a pair of LA-style aluminium Commando heads, part number P5153849. These heads are equipped with 2.020-inch stainless steel intake valves and 1.600-inch stainless steel exhaust valves, providing excellent flow characteristics. Being LA-style heads, they utilise traditional shaft-mounted stamped-steel rocker arms, maintaining the vintage aesthetic and functional design.
• Camshaft: The engine incorporates a hydraulic flat tappet camshaft, part number P4120233. This cam boasts a .508/.508-inch lift and a duration at .050 inch of .248/.248 degrees. Affectionately known as the "Purple Shaft" cam, this particular grind has been a staple in Mopar performance for a very long time, proving its effectiveness and reliability through decades of use. Its specifications contribute significantly to the engine's broad power band and impressive top-end performance.
• Induction System: Perhaps the most visually impactful and performance-defining feature of the original 340 was its Six Pack induction. Mopar has faithfully replicated this, making the Six Pack the induction system of choice for the new engine. The intake manifold, part number P4529054, is the same tried-and-tested design used previously and is ready for carburettor installation. It's important to note that the carburetors and linkage are not included with the crate engine but are readily available from aftermarket suppliers. For instance, Holley carburetors are a common choice, and linkage kits and air filter assemblies can be sourced from specialists like YearOne.
• Ancillaries: Finishing off the engine are a stock-style oil pan and attractive cast aluminium valve covers. The choice to use LA-style heads and valve covers is particularly welcome, as it preserves the authentic, vintage look of a true 340 Six Pack engine, rather than opting for the more modern, but visually different, Magnum-style components.

Dyno Testing: Proving the Mopar 340's True Potential

While Mopar's official ratings for the new 340 Six Pack stand at a respectable 330 hp and 330 lb/ft of torque, the real-world performance on a dyno tells an even more exciting story. Independent testing has consistently shown that this engine delivers significantly more power than claimed, making it an even more enticing proposition for enthusiasts.

During a comprehensive dyno session, after receiving the engine and installing the necessary Holley carburetors, linkage kit, and air filter assembly (sourced from YearOne), the engine was prepared for testing. Initially, there were some concerns about whether this new 340 could truly live up to the legendary reputation of its predecessor. After priming the oil system, checking for leaks, and finally firing it up, the engine sounded surprisingly mild, idling smoothly at around 850 rpm after some minor tweaks – much like a basically stock small-block.

Initial pulls were made up to 5,000 rpm to gauge its behaviour and establish baseline tuning. At 5,200 rpm, the engine produced 295.1 hp and 292.1 lb/ft of torque. This was a good starting point, but the true potential was yet to be unlocked. Pushing the engine further to 6,000 rpm yielded 320.4 hp, just shy of Mopar's stated 330 hp. This prompted further adjustments.

The first significant gain came from optimising the ignition timing. Initial pulls had the timing set around a safe 32 degrees. By bumping this up to 34 degrees, the engine responded enthusiastically, immediately delivering 335.3 hp – exceeding Mopar's claim with a simple timing adjustment!

Further gains were achieved through meticulous carburettor jetting. A smart modification involved installing Promax Carbs' jet plates in the outboard carburetors. This ingenious solution allows for the use of standard Holley carburetor jets, simplifying the process of fine-tuning fuel delivery without the risk and hassle of drilling metering plates. After several jet changes and a final timing adjustment to 35 degrees, the engine reached its peak performance.

Dyno Results Summary

At the conclusion of the dyno session, the new 340 Six Pack crate engine achieved an astonishing total of 388.5 hp at 6,800 rpm and 397.3 lb/ft of torque at 4,200 rpm. This remarkable outcome demonstrates that Mopar's initial ratings were indeed conservative. The fact that the tried and true flat-tappet "Purple Shaft" cam willingly spun to 6,800 rpm was particularly impressive, showcasing its robust design. Ultimately, the testing revealed an additional 58 hp and over 63 lb/ft of torque beyond Mopar's claims – a fantastic bonus for any enthusiast!

Frequently Asked Questions (FAQs)

Q: Is the new Mopar 340 replacement block a direct fit for original 340 applications?
A: Yes, the block (PN P5007552AB) is machined to work with all 340 production components. However, it may require a Mopar PN 05281090BA oil filter or equivalent, and potentially a late '70s 318 motor mount on the left side for some installations.

Q: Can I use modern roller tappets with the new 340 replacement block?
A: No, the Mopar Performance 340 replacement block is explicitly not recommended for use with roller tappets. Its design is optimised for hydraulic flat tappet camshafts, such as the included "Purple Shaft" cam.

Q: What type of fuel does the new Mopar 340 Six Pack engine require?
A: With a compression ratio of 10.0:1, the new 340 is well within the acceptable range for using Premium pump fuel (typically 95-98 RON in the UK) from your local petrol station.

Q: Are the carburetors and linkage included with the Mopar 340 Six Pack crate engine?
A: No, the carburetors and linkage for the Six Pack induction system are not included with the crate engine. They need to be purchased separately, with popular choices being Holley carburetors and linkage kits from aftermarket suppliers like YearOne.

Q: How does the new Mopar 340 Six Pack engine compare to the original 1970 340?
A: The new 340 Six Pack builds upon the original's legacy with modern manufacturing and design refinements while retaining its vintage character. While the original 1970 340 Six Pack was rated at 290 hp, the new version is officially rated at 330 hp, and independent dyno testing has shown it can produce closer to 388 hp with proper tuning, offering significantly more power and potentially greater durability due to features like high nickel content in the block and four-bolt main caps.

Conclusion

The Mopar 340, a true legend in the world of high-performance engines, continues to captivate enthusiasts with its blend of heritage, robust construction, and formidable power. Whether you're seeking a complete, factory-fresh Mopar 340 Six Pack crate engine directly from Mopar Performance, or planning an ambitious build with a high-quality stroker kit from a specialist like CNC-Motorsports, the options for bringing this iconic powerplant to life are more accessible than ever. The new replacement block, with its enhanced features and compatibility with original components, provides an exceptional foundation for any project. And as the dyno results unequivocally demonstrate, with the right tuning, the modern 340 is more than capable of exceeding expectations, delivering exhilarating horsepower and torque that will undoubtedly put a smile on any driver's face. Embark on your Mopar journey with confidence, knowing that the spirit of the 340 lives on, ready to roar into action.

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