The TR5's Six-Cylinder Secret: A British Icon

For enthusiasts of classic British sports cars, the Triumph TR series holds a special place, representing a blend of raw power, distinctive styling, and driving purity. Among these revered models, the TR5 stands out, often celebrated for its potent engine and short, but impactful, production run. If you've ever wondered about the beating heart beneath its elegant bonnet, you're in the right place to uncover the mechanical marvel that defined this particular chapter in Triumph's storied history.

How Many Cylinders Does a TR5 Have?

To answer directly: the Triumph TR5 is famously equipped with a six-cylinder engine. This was a significant step up from its four-cylinder predecessors in the TR range, marking a new era of performance for the marque. Introduced in 1967, the TR5, alongside its American counterpart the TR250, brought a new level of sophistication and power to the long-standing TR lineage.

The Evolutionary Trail: From TR2 to TR5

The TR5 wasn't just a standalone model; it was a crucial link in a long evolutionary chain that began way back in the early 1950s. The story truly started in 1952 when Harry Webster's design team, complemented by body designer Walter Belgrove, unveiled their vision for a new 'Triumph Sports Car' at Earls Court. The positive public reception spurred the team to develop a production model, which debuted as the TR2 at Geneva.

The TR2 was built on a sturdy Flying Standard Nine chassis, utilising front suspension from the old Triumph Mayflower and powered by a Standard Vanguard wet liner engine. This model set the stage for a continuous process of refinement and evolution.

Facelifts and Engine Tweaks: TR3 and TR3A

Following the TR2, minor facelifts and engine alterations led to the TR3 and TR3A models. These iterations maintained the core spirit of the original but incorporated improvements that kept the TR competitive and desirable. The evolutionary process was subtle but constant, laying the groundwork for more significant changes to come.

A More Sophisticated Beast: The TR4 and TR4A

In 1961, the TR series took a significant leap forward with the introduction of the TR4, styled by the renowned Giovanni Michelotti. While the bodywork was fresh and modern, underneath, it was still essentially the original TR, albeit with ongoing refinements. The TR4 offered a more contemporary look and feel, broadening its appeal.

The 1965 TR4A may have looked similar to the TR4, but it featured a transformative redeveloped chassis and, crucially, independent rear suspension (IRS). This was a major engineering upgrade, significantly improving ride comfort and handling. Interestingly, in the US market, the new "bell" chassis was slightly modified to retain the older live rear axle, as it was believed that American drivers might not appreciate the more sporting characteristics of the new IRS axle.

The Dawn of Six Cylinders: The TR5 and TR250

Just two years after the TR4A, in 1967, Triumph introduced the TR5 (and the TR250 for the American market). This was the moment the six-cylinder engine made its grand entrance into the TR lineup. Powering these new models was a formidable 2.5-litre, straight-six engine. This engine transformed the TR's performance, giving it a new lease of life and cementing its status as a serious sports car. The TR5, in particular, featured Lucas mechanical fuel injection, which was quite advanced for its time and contributed to its impressive power output.

The TR5's production run was remarkably short, lasting only fifteen months. Despite its brevity, it established a new benchmark for performance within the TR series, making it a highly sought-after classic today. The TR250, sold in the US, used twin Stromberg carburettors instead of fuel injection due to emission regulations and cost considerations, resulting in a lower power output but maintaining the six-cylinder configuration.

The Six-Cylinder Engine: A Deep Dive

It’s truly remarkable to trace the lineage of the six-cylinder engine that powered the TR5, TR250, and later the TR6. Its humble beginnings can be found in the 803cc Standard 8 engine of 1954. Harry Webster's original four-cylinder engine evolved significantly, eventually growing into a 1500cc unit used in cars like the Triumph Herald, Spitfire, and even the MG Midget.

Along this journey, the engine gained two extra cylinders, increasing its capacity to 1998cc. In this form, it powered models such as the Vanguard Six, Triumph 2000, and GT6, and initially, in a reduced capacity, the Vitesse. However, for use in the TR, the engine demanded even greater performance.

While rally-tuned Triumph 2000s were achieving 150 bhp with triple Weber carburettors, this came at the expense of fuel economy. The entire family of engines on which the TR unit was based shared a stroke of 76mm. To achieve the desired performance for the TR, the only way forward was to increase the stroke significantly to 95mm. This was a bold move, flying in the face of conventional modern engine design at the time. To accommodate this, the engine block was extensively modified to house a new crankshaft, and simultaneously, the cylinder head underwent a complete redevelopment.

Performance and Technical Specifications

With a slightly wild camshaft, the new fuel-injected engine in the TR5 delivered an impressive 150 bhp. This made the TR5 a truly quick car for its era. The carburetted "Federal" version, found in the TR250, offered 104 bhp, a considerable difference due to the less sophisticated fuel delivery system and emissions compliance requirements.

Triumph used specific engine prefixes to distinguish between these variants: the Lucas fuel-injected cars were given an engine prefix of CP, while the carburetted versions had a prefix of CC. In 1973, with the introduction of a milder camshaft (aimed at improving TR performance in heavy traffic), these prefixes changed from CP to CR and CC to CF respectively.

Compression ratios also varied. The fuel-injected cars maintained a robust compression ratio of 9.5:1, contributing to their higher power output. Federal cars, however, began life with a ratio of 8.6:1, which was further reduced to 7.75:1 in 1971 (coupled with new Stromberg 175 CDSE(2) carburetters), and then to 7.5:1 in 1973 (this time fitted with Stromberg 175 SEV carburetters). These reductions were primarily driven by increasingly stringent exhaust and emission restrictions, which gradually stifled the performance of Federal/Californian cars, eventually bringing them down to TR4 performance standards, despite the larger engine.

The TR6: Building on the TR5's Legacy

The TR5/250's short lifespan led to its replacement by the TR6 in November 1968. While Michelotti was unavailable to design the TR6 body, Karmann of West Germany was selected. The new TR6 ingeniously used the same chassis, inner shell, screen, and even the same doors as the TR5. This meant that the TR6 retained the TR5's powerful six-cylinder engine and much of its underpinnings, albeit with refined suspension geometry and the addition of an anti-roll bar.

The TR6 continued the tradition of the six-cylinder engine, becoming the most popular of the TR range. Its production ran until 1975 (1976 for Federal versions), showcasing the enduring appeal of the six-cylinder TR platform. The availability of parts for the entire TR range, including the TR5 and TR6, is better than ever, thanks to dedicated enthusiasts and specialists worldwide who ensure these classics remain on the road.

Triumph TR Model Comparison

To better understand the TR5's place in the lineage, here's a brief comparison of key models:

Frequently Asked Questions About the TR5

What makes the TR5 special compared to other TR models?

The TR5 is special primarily because it was the first TR to feature a six-cylinder engine, specifically the powerful 2.5-litre unit with Lucas mechanical fuel injection. This combination gave it significantly more power (150 bhp) than its four-cylinder predecessors and its carburetted American counterpart (TR250), making it a truly exhilarating drive. Its very short production run also adds to its rarity and desirability among collectors.

What's the difference between a TR5 and a TR250?

Both the TR5 and TR250 were introduced at the same time and share the same chassis and six-cylinder, 2.5-litre engine. The key difference lies in their fuel delivery systems and target markets. The TR5, primarily sold in the UK and Europe, featured Lucas mechanical fuel injection, producing 150 bhp. The TR250, sold in the North American market, used twin Stromberg carburettors to comply with US emissions regulations, resulting in a lower output of 104 bhp.

Was the TR5 engine designed specifically for the TR?

While the six-cylinder engine in the TR5 was based on a long-evolving Standard engine family (dating back to the 803cc Standard 8), it underwent significant modifications for TR use. The most notable change was an increase in stroke from 76mm to 95mm, requiring a new crankshaft and extensively modified block. The cylinder head was also completely redeveloped to meet the TR's performance demands, making it a highly adapted and powerful unit for the sports car.

Is it difficult to find parts for a TR5 today?

Despite its age and short production run, finding parts for a TR5 is generally not as difficult as one might expect for such a classic. The TR5 shares many components with the more common TR6, and there's a thriving global network of Triumph specialists and parts suppliers. Many parts are reproduced, often to a higher standard than the originals due to modern materials, and old tooling is continually being rediscovered and utilised. This strong enthusiast community ensures excellent technical support and parts availability for TR owners.

What was the power output of the TR5?

The Triumph TR5, with its Lucas mechanical fuel injection, produced a healthy 150 bhp (brake horsepower). This made it a very capable and fast sports car for its time, especially when compared to its contemporaries and its four-cylinder predecessors.

Why was the TR5 replaced so quickly by the TR6?

The TR5's rapid replacement by the TR6 after only fifteen months was primarily due to a combination of factors, including evolving styling trends and production efficiencies. While the TR5 was mechanically advanced, Triumph wanted to update its appearance. Karmann of West Germany was tasked with redesigning the bodywork, resulting in the TR6, which shared many underpinnings (chassis, inner shell, doors, engine) with the TR5, making for a relatively quick transition in production.

The Triumph TR5, with its powerful six-cylinder engine, represents a pivotal moment in the TR lineage. It blended classic British sports car charm with a significant boost in performance, setting the stage for the highly successful TR6. Its legacy endures, cherished by enthusiasts for its distinctive character and the exhilarating roar of its six-pot heart.

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