Supercharge Your TR6: Unlocking Hidden Power

The Triumph TR6, with its quintessential British roadster charm and robust inline-six engine, has long been a beloved classic. While often lauded for its distinctive styling and torquey delivery, many enthusiasts find themselves yearning for a little more zest, a sharper edge to its performance. As the values of other six-cylinder British sports cars like the Jaguar E-type and Big Healey soar, the TR6 remains an accessible gem with immense performance potential. This article delves into how supercharging can unlock that potential, transforming a capable classic into a truly exhilarating machine, far beyond mere capital appreciation.

Understanding the TR6 Drivetrain

At its heart, the Triumph TR6 is propelled by a 2.5-litre inline-six engine. In its standard, naturally aspirated form, particularly the U.S.-spec models, this engine is known more for its low-compression, torquey nature than for outright horsepower. Factory figures for American-market TR6s typically hovered around 102 to 106 horsepower at the crank, a respectable but not thrilling output for a sports car. British models, benefiting from Lucas fuel injection, managed a more spirited 150 horsepower. This inherent characteristic of the TR6 engine – its robust torque delivery coupled with a relatively modest power output – makes it an ideal candidate for forced induction. It has the foundation to handle additional power, and the gains from a supercharger are genuinely transformative, allowing the engine to breathe and perform at a level it was perhaps always capable of.

The Science of Boost: Why Supercharge?

To truly understand the magic of supercharging, one must first grasp a fundamental principle of engine operation: an engine functions like an air pump. The more air you can efficiently move through it, the more fuel it can burn, and consequently, the more power it can generate. Most classic car engines achieve optimal power when the air-to-fuel ratio is around 12.5 parts air to 1 part fuel. Consider this: for every pound of fuel (roughly one pint), you need approximately 12.5 pounds of air. At sea level, that’s about 170 cubic feet of air – a substantial volume to force through relatively small valves, often less than two inches in diameter.

How Superchargers Work

Traditional methods for increasing air intake in naturally aspirated engines involve optimising the pathways into the engine. This includes porting the cylinder head, increasing carburettor sizes, and enlarging valve and port dimensions. Another approach is to increase valve lift, which boosts the potential volume through the valve opening, or to extend valve opening duration, giving air more time to enter the cylinders. While these methods are effective, they rely on the engine *sucking* air in, a process that inherently faces limitations. This is where superchargers enter the fray. They take a proactive approach, actively pumping or compressing air before it even enters the engine. By doing so, they dramatically increase the volume of air available for combustion, allowing the engine to burn more fuel and generate significantly more power.

Potential Drawbacks of Forced Induction

While the allure of boosted power is undeniable, it’s crucial to acknowledge the inherent drawbacks of supercharging. Firstly, there's the cost and complexity. Supercharger kits are a significant investment, often running into several thousand pounds, and they introduce additional moving parts to the engine, increasing the potential for mechanical issues. Secondly, superchargers suffer from parasitic loss. It takes power from the engine itself to spin the supercharger. The amount varies depending on the unit, but it's a factor that reduces the net power gain. Finally, and perhaps most critically, is the issue of heat. Compressing air inherently heats it up. This elevated air temperature can reduce power and, more dangerously, significantly increase the likelihood of detonation. Detonation, or ‘knocking’, is an uncontrolled combustion event that not only robs power but can cause severe, often catastrophic, engine damage.

Modern Supercharging Solutions

Despite the challenges, supercharging has evolved considerably, becoming a near 'silver bullet' for many performance applications. Modern blowers are far more efficient, compact, reliable, and cost-effective than their predecessors. They are often designed to work seamlessly with stock or near-stock engines, providing excellent performance and drivability across a wide RPM range. Unlike many naturally aspirated power-adders that build power at higher engine speeds, superchargers typically deliver significant gains at much lower RPMs, making the increased power far more usable and enjoyable in everyday street driving scenarios. This evolution has led to a growing number of aftermarket manufacturers offering supercharger kits for classic cars, including the Triumph TR6, making performance upgrades more accessible than ever before.

The Moss Supercharger Kit for TR6

Among the various options available for boosting British classics, the Moss supercharger kit for the TR6 stands out for its comprehensive nature. It is renowned for being a truly complete kit, including every single component down to the last nut, bolt, and hose clamp. The core of the system is the highly regarded Eaton MP62 supercharger, a unit widely utilised in modern vehicles and across the aftermarket industry. This specific supercharger is chosen for its ability to deliver a balanced blend of performance, drivability, and longevity when paired with a stock TR6 engine in a milder state of tune.

The Moss kit features a custom manifold setup and a sophisticated drive system that upgrades the TR6's traditional V-belt to a modern, multi-ribbed serpentine belt. This conversion necessitates new pulleys for both the water pump and the alternator, which are included in the kit, along with various brackets, idlers, and a crucial spring-loaded auto-tensioner to maintain optimal belt tension. For fuel delivery, Moss deviates from the traditional SU carburettors found in many of their other kits, opting instead for an American Holley carb. The supplied 350 cfm manual-choke, two-barrel Holley is a practical choice, as tune-up and rebuild parts are readily available at most automotive parts stores. To ensure adequate fuel supply to this carburettor, an electric fuel pump is also included, along with a block-off plate for the original mechanical unit. The kit is topped off with a simple yet effective chrome-topped, paper element air filter, which has been shown in testing to perform comparably to much more expensive K&N units.

The Moss supercharger kit is available in two versions: one for 1969-’71 TR6 models (part No. 150-108) and another for 1972-’76 models (part No. 150-118), both priced at £3495. For those seeking even greater boost, Moss offers an optional smaller pulley (part No. 150-112, £144) that provides an additional 2 psi. To combat the heat generated by compression, a heat shield kit (part No. 150-106, £86) designed to sit between the blower and manifolds is also available, a highly recommended addition for preserving engine health.

Installation Insights and Practical Tips

Despite the comprehensive 46-page instruction manual and the sheer number of parts, the installation of the Moss supercharger kit is remarkably straightforward for a reasonably experienced home mechanic. The process begins with the removal of the radiator, front chassis crossmember, and the original pulley system, followed by the intake manifold and carburettors. The new components are then installed: the water pump and new pulleys, and the Eaton blower and its manifold, which directly replace the stock setup. The chassis crossmember and radiator are then reinstalled, with careful attention to hose routing. The mechanical fuel pump is removed from the engine block, and its mounting hole is sealed off with the provided block-off plate. The new electric fuel pump is then installed, plumbed, and wired. Finally, the bonnet is reinstalled, marking the completion of the physical installation.

While the Moss kit is exceptionally well-engineered, some installers, including the author, have taken slight liberties with certain installation details to optimise the setup. For instance, the instruction manual suggests mounting the electric fuel pump to a chassis member behind the left-rear tyre. However, this location can expose the pump to road spray and requires extensive rerouting of wiring and fuel lines. A more practical approach, adopted by the author, is to mount the pump under the bonnet, close to its original location on the engine block, perhaps on the left-front inner fenderwell. This keeps the pump out of harm's way, significantly shortens wiring runs, and allows for the retention of most of the original fuel lines.

Wiring the fuel pump also presents an opportunity for customisation. Instead of relying solely on the included fuse, one might leverage the TR6's existing wiring, which often provides two fused circuits. Utilising the purple circuit for a fused, main power source and the green circuit for a fused, switched source that controls the relay and pump can result in a neater and more robust electrical installation. Furthermore, addressing crankcase breathing is a crucial, often overlooked, detail. Many aftermarket carburettor setups, including this kit, may lack provisions for positive crankcase ventilation (PCV), instead directing breather hoses to the air filter. While this vents the crankcase, it can lead to oily air filters and fumes. Installing an inline PCV valve (such as NAPA Part No. 2-9209) and connecting it to a manifold vacuum port on the carburettor provides a far more effective and cleaner solution for crankcase ventilation.

Optimising Performance: The Power of Tuning

Simply bolting a supercharger onto an engine is only half the battle; the true gains in power and drivability come from a meticulous performance tune. Factory specifications for timing and carburettor settings are often irrelevant when significantly altering an engine's induction system. A proper performance tune begins with optimising the ignition system, identifying the correct initial timing, advance curve, and maximum timing. Once the ignition is dialled in, attention shifts to the carburettor. Achieving the correct jetting across the entire power range, not just at idle, is paramount. Incorrect jetting can lead to issues ranging from a smoking exhaust to severe engine damage; optimal jetting, however, translates directly to smoking tyres – a far more desirable outcome.

The author's experience perfectly illustrates this point. Before the supercharger installation, their well-tuned TR6 produced a respectable 89 horsepower at the wheels and achieved a 0-60 mph time of 10.3 seconds. After installing the supercharger, initial 0-60 times were a disappointing 10.0 seconds – a negligible improvement for a £3500 investment. The issue was quickly identified: the supplied carburettor jetting was too rich. Through a process of leaning out the carburettor, 0-60 times steadily improved, eventually plummeting to 8.3 seconds. A few hours of work and just £20 worth of jets yielded a dramatic difference.

Further refinement on a chassis dyno allowed for the extraction of every last bit of power. An initial dyno run showed 108 horsepower at the wheels. Adjusting the total timing from 33 degrees to 37 degrees alone added another 5 horsepower. Subsequent adjustments to the air/fuel ratios, by going two jet sizes leaner, yielded an additional 5 horsepower. This dyno session resulted in a combined 10 horsepower increase, further reducing 0-60 times. The takeaway is clear: the supercharger provides the potential, but a carefully executed performance tune unlocks the maximum benefit. Budgeting for professional tuning, ideally with dyno time, is highly recommended for any significant power upgrade.

Performance Data Comparison

To truly appreciate the impact of supercharging, let’s look at the numbers. The table below compares the performance of a stock TR6, the author's initially hot-rodded naturally aspirated TR6, and the supercharged variants:

As evident from the figures, the transformation is remarkable. The 0-60 mph time drops from over 10 seconds to a blistering 6.3 seconds, putting the TR6 into a completely different league of performance. Horsepower climbs from a baseline of 89 to 131 at the wheels, with a significant increase in torque, ensuring the car pulls like a freight train throughout the rev range. Despite these dramatic gains, the drivability remains excellent, with quick starts and a smooth idle, feeling like a strong stock engine until the throttle is truly opened.

Addressing Common Supercharger Myths

One of the most persistent urban legends surrounding superchargers is the notion that they inherently 'blow up' engines. This is a significant misconception. While engine failures can occur in supercharged vehicles, the supercharger itself is rarely the direct cause. Instead, failures almost invariably stem from other underlying issues, primarily detonation.

Will a Supercharger Destroy My Engine? (FAQs)

Q: Does a supercharger automatically lead to engine failure?

A: No. While supercharging increases stress on an engine, it is rarely the direct cause of failure. The primary culprit in most supercharged engine failures is uncontrolled detonation.

Q: What causes detonation in a supercharged engine?

A: Detonation typically arises from improper tuning. This includes having too much ignition timing advance, or a fuel mixture that is too lean at high RPMs. Either scenario can lead to uncontrolled, damaging combustion within the cylinders.

Q: Can I supercharge any engine?

A: Not ideally. An engine must be suitable for forced induction. For instance, an engine with too high a static compression ratio for the amount of boost being applied is highly susceptible to detonation and subsequent damage. Optimisation of the engine's internals for boost is crucial for reliability.

Q: Do superchargers destroy connecting rods, bearings, and crankshafts?

A: In typical street applications at boost levels below 12 psi, damage to the bottom end (rods, bearings, cranks) is uncommon directly due to the supercharger. Sustained high engine speeds, regardless of the induction system, are generally harder on the bottom end. With most superchargers, significant torque and power are produced at lower engine speeds, reducing the need for prolonged high-RPM operation to achieve spirited performance.

Q: How can I ensure my supercharged engine is reliable?

A: Ensure your engine is suitable for boost, that the supercharger kit is installed correctly, and, most importantly, that the engine receives a professional and meticulous tune. Keeping the engine within its safe operating parameters (e.g., below redline) also contributes significantly to longevity.

In essence, if your engine is properly suited for boosted applications, meticulously tuned, and operated responsibly within its design limits, a supercharger is highly unlikely to cause catastrophic failure. It's the combination of appropriate components and expert calibration that ensures both thrilling performance and enduring reliability.

Beyond Supercharging: Other TR6 Power Upgrades

While supercharging offers a dramatic leap in performance, it's not the sole path to waking up a TR6. For years, enthusiasts have employed more traditional methods to enhance the TR6's power output, often with impressive results. The TR6 engine responds exceptionally well to upgrades such as cylinder head porting, which improves airflow, and increases in compression ratio. Camshaft upgrades are another popular modification, altering valve lift and duration to optimise power delivery. Furthermore, improvements to both the induction system (e.g., larger carburettors or throttle bodies) and the exhaust system (e.g., headers and free-flowing mufflers) can yield significant gains. However, it's crucial to approach these modifications with a clear performance objective in mind, as haphazardly throwing parts at the car can lead to an unbalanced or even detrimental outcome. A well-planned and synergistic combination of upgrades is always recommended to achieve optimal results.

In conclusion, supercharging a Triumph TR6 offers an unparalleled transformation in performance, turning a classic British sports car into a formidable and genuinely thrilling machine. The Moss supercharger kit provides a comprehensive and well-engineered solution, and with careful installation and, crucially, a professional performance tune, the results are nothing short of astounding. The significant gains in horsepower and torque, coupled with dramatically improved acceleration, redefine the TR6 driving experience. While the investment is substantial, the power gained per pound spent is highly competitive with other power-adders. For the TR6 enthusiast seeking to truly unleash their car's hidden potential and experience modern performance in a classic package, supercharging stands as a highly recommended upgrade.

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