The Mighty Imp: Unveiling Its 1967 Power

In the annals of British motoring history, the Hillman Imp, often associated with its diminutive size and plucky nature, occasionally hides a remarkable secret: its capacity for surprising power. While many remember the standard family saloon, a select few were privy to versions that packed a serious punch, particularly in 1967. This era saw the Imp, especially when equipped with pioneering fuel injection technology, evolve from a humble commuter into a formidable performer, capable of challenging much larger and supposedly more powerful vehicles.

The Imp's Hidden Muscle: Unveiling the Power Figures

For a car of its stature, the power outputs achieved by certain 1967 Hillman Imps were truly exceptional. This was largely thanks to dedicated engineering and the adoption of advanced fuel delivery systems, pushing the boundaries of what was expected from a compact rear-engined car.

Nathan Engine Outputs with Fuel Injection

One of the most notable configurations was the Nathan twin overhead camshaft Imp engine, specifically fitted with Tecalemit-Jackson fuel injection. This combination yielded impressive figures:

• The 849cc version of this engine produced a robust 98 bhp.
• Stepping up in displacement, the 998cc variant delivered an even more remarkable 125 bhp.

To put this into perspective, achieving close to 100 bhp from an 850cc engine, or 125 bhp from a 1-litre unit, was a considerable feat in the mid-1960s, particularly for a production-derived engine. These figures highlight the significant impact of the fuel injection system.

The Elusive Rootes Prototype: Peter Harper's Experience

Adding to the legend of the powerful Imp is the intriguing account from Peter Harper, who was tasked with testing a Hillman Imp that Rootes had converted to fuel injection. Harper's testimony paints a vivid picture of its capabilities:

"He used to cause havoc on the motorways, waited for some high powered car to come past at speed, he waited until they were some distance in front then put his foot down, overtook the car like a bullet and left sufficient turbulence to cause a panic attack."

Harper reported that this prototype Imp developed an astonishing 130 bhp in what he described as "standard form." This suggests an internal Rootes development that, regrettably, never made it to full production. The Rapier also converted with the same system was equally impressive, leading Harper to express disbelief that such a potent system wasn't commercialised. The system in question was being developed by Tecalemit, further underscoring their pioneering work in the field.

Fraser Mechanics' Enhancements: John Griffiths' Rally Imp

Beyond factory and prototype efforts, independent tuners also pushed the Imp's boundaries. By the end of 1967, John Griffiths, one of the Fraser mechanics, had significantly boosted the power of his Imp. Over one and a half seasons, he increased its output from 95 bhp to almost 120 bhp. This power surge was achieved through a combination of:

• A large-valve, high-compression cylinder head
• A racing camshaft
• And, critically, Tecalemit-Jackson fuel injection.

This particular Imp was also capable of safely revving up to an impressive 9,000 rpm, a testament to the robust engineering and the precise fuel delivery offered by the injection system.

Here's a comparative overview of these impressive power figures:

The Heart of Performance: Fuel Injection's Role

The consistent thread running through these high-performance Imp variants is the presence of fuel injection. In an era dominated by carburettors, fuel injection offered significant advantages, particularly for racing and high-performance applications. Carburettors, while simpler, are inherently less precise in fuel metering, especially across varying engine speeds and loads. They are also susceptible to fuel starvation or flooding during hard cornering or under heavy acceleration. Fuel injection, by delivering fuel directly or very close to the intake valve, allows for much finer control over the air-fuel mixture, leading to more efficient combustion, better throttle response, and ultimately, more power.

The ability to precisely control fuel delivery meant that engines could be run closer to their optimal air-fuel ratio, even at high RPMs or under sudden changes in throttle position. This precision minimised wasted fuel and maximised the energy extracted from each drop of petrol, contributing directly to the impressive horsepower figures achieved by these modified Imps. Furthermore, the improved atomisation of fuel, even if not perfectly ideal in early systems, still offered a significant step up from carburettor designs.

Tecalemit-Jackson: Pioneering Performance

The Tecalemit-Jackson (TJ) system was a key player in the Imp's performance story. Unlike modern sequential, timed injection systems, the TJ unit was an "untimed" system. This meant it delivered a continuous spray of petrol into the manifold, with the amount governed by engine speed and throttle opening. While this might seem less efficient on paper, in practice, the petrol would linger in the manifold until the inlet valve opened, at which point it would be drawn into the cylinder and combusted. This approach, though not perfectly atomised, still offered a significant gain over conventional carburettors.

How the Tecalemit-Jackson System Worked

The TJ system was a complex mechanical and hydraulic marvel for its time. Here's a simplified breakdown of its operation:

1. Electric Pump (1): Mounted under the floor, an electric gear pump initiated the process, pushing fuel at a basic pressure of 25-30 psi.
2. Fuel Filter (2): The fuel then passed through a filter to ensure cleanliness.
3. Non-Return 'Check & Bleed' Valve (3): This valve maintained pressure and prevented backflow.
4. Engine-Driven Mechanical Pump (4): This was the heart of the system, driven off the crankshaft by a toothed belt. When stationary, fuel would pass through it. When the engine started turning, this pump would begin to revolve, significantly increasing the fuel pressure.
5. Pulse Unit (5): As the electric pump built pressure, a diaphragm valve within the pulse unit would open, allowing fuel to circulate through the system even when the engine was off (priming the system). When the engine-driven pump started, it would send a pulse to close a valve in the pulse unit, increasing the overall system pressure.
6. Relief Valve Unit (6): This unit helped regulate pressure and allowed excess fuel to return to the tank via pipe (7).
7. Control Unit (10): This was the brain of the system, a finely machined fuel tap connected via linkages to the throttle butterflies and the accelerator pedal. Inside, cams operated a main metering valve, controlling the primary fuel flow based on throttle position and engine speed.
8. Equalising Valve (8): This was the final step before the fuel reached the rail distributor. It would only open when sufficient pressure was built up by the engine-driven pump.
9. Rail Distributor (9) and Nozzles: From the equalising valve, fuel entered the rail distributor, which then directed it to individual nozzles, spraying into each cylinder's intake manifold.
10. Acceleration Device (11, 12): A cam inside the control unit also operated a diaphragm valve, fed by pipe (12). This acted like an acceleration pump in a carburettor, delivering an extra squirt of fuel along line (11) to the equalising valve, enriching the mixture during acceleration phases.

Advantages and Challenges of Early Fuel Injection

The TJ system, despite its complexity, offered clear advantages. It provided a definite gain in power over carburettor-fed engines, particularly at higher RPMs, and could maintain consistent fuel consumption comparable to an equivalent atmospheric engine when properly set up. The untimed continuous flow, while seemingly inefficient, proved effective in practice, with fuel eventually being drawn in and burnt.

However, the system presented significant challenges, particularly in setup and adjustment. Tecalemit themselves admitted that a major improvement in power often came from having a decently shaped manifold, rather than the injection system itself. The main hurdle was the "practically insuperable obstacle of adjusting the mixture strength." Without modern electronic sensors and feedback loops, setting the system up decently required extremely expensive bench trials by experts. Fine-tuning involved adjusting elements like the tick-over fuel pressure (via a knob adjusting a valve in the pulse unit) and the main restrictor in the delivery pipe, which controlled full-bore flow. These critical adjustments could only be accurately determined by specialists using sophisticated brake-testing equipment.

Beyond TJ: Other Fuel Injection Innovations

While Tecalemit-Jackson was prominent, other fuel injection experiments and applications also contributed to the Imp's high-performance narrative:

• Volvo 244 System Conversion: Nick Cleak's turbocharged 1-litre Imp famously ran for over a decade using a fuel injection system from a Volvo 244 (2.3-litre). This unconventional swap proved highly effective, offering "perfect cold starts and no stalling or rough running when cold." This demonstrates the adaptability and potential benefits of adapting systems from other vehicles.
• MegaSquirt Electronic Fuel Injection: While perhaps not from 1967, the mention of MegaSquirt highlights the enduring interest in fuel injection for Imps. This open-source DIY EFI controller provides complete hardware and software plans for enthusiasts to build their own systems, a testament to the community's desire for modern, precise fuel management.
• Weber Alpha Fuel Injection: Gerald Stanley's racing G15 and the Clan Q516 UHB (for sale in 2009) were modified with Weber Alpha Fuel Injection Systems, showcasing the use of more widely recognised performance injection brands on Imp-derived vehicles.
• Bill Wanderer's Slide Valve Injection: 'Mr. Bill', a legendary figure in boat racing, developed slide valve fuel injection systems for the Imp and other engines. Slide valve systems offer extremely precise and rapid fuel delivery, often used in high-performance racing applications.
• Lucas P.I. and CAV: The text also briefly mentions Lucas P.I. (Petrol Injection) systems, another prominent British injection manufacturer, and Peter Ware's prior work on fuel injection systems for Leyland and CAV before joining Rootes in 1958.

Rallying to Victory: Proving Ground for Performance

The significant power gains achieved through fuel injection weren't just theoretical; they translated into tangible success on the rally stages. The demanding conditions of rallycross and rallying provided the perfect proving ground for the Imp's enhanced capabilities:

• In the Player's No. 6 National Rallycross Championship of January 1968, Dave Lambert scored points in the southern area with his fuel-injected Rallye Imp, demonstrating its competitive edge.
• Perhaps even more significantly, Ron Beswick & Stuart Preacher triumphed in the 1974 Cambrian Rally in a 998cc Hillman Imp PI (petrol injection). All the competition preparation for this winning car was done by Skip Brown, a good friend of Ron, underscoring the role of expert tuning alongside the advanced fuel system.

These victories cemented the fuel-injected Imp's reputation as a serious contender, punching well above its weight class.

Frequently Asked Questions (FAQs)

Was fuel injection common on cars in 1967?

No, fuel injection was quite rare and advanced for mainstream production cars in 1967. It was primarily found in high-performance, luxury, or racing vehicles due to its complexity and cost. Carburettors were the standard fuel delivery method for the vast majority of vehicles, especially small economy cars like the Imp. The Imp's use of fuel injection, even in limited or experimental forms, was indicative of its forward-thinking design and performance potential.

Why was fuel injection so important for the Imp's performance?

For the Imp, fuel injection offered several critical advantages that carburettors couldn't match. It allowed for much more precise fuel metering, leading to better throttle response, improved fuel atomisation, and more consistent air-fuel ratios across the entire RPM range. This precision minimised fuel waste and maximised power output, particularly at high engine speeds where carburettors often struggle. It also facilitated better cold starts and smoother running, as evidenced by Nick Cleak's Volvo-injected Imp.

Is it possible to add fuel injection to a classic Imp today?

Yes, it is definitely possible, and a popular modification among Imp enthusiasts. While original Tecalemit-Jackson systems are incredibly rare and complex to maintain, modern electronic fuel injection (EFI) systems, such as those based on MegaSquirt, or adapted systems from other vehicles, offer a more reliable and tuneable solution. These modern systems provide superior performance, fuel economy, and drivability compared to period carburettors, making them an attractive upgrade for a classic Imp.

What were the main challenges with early fuel injection systems like Tecalemit-Jackson?

Early mechanical fuel injection systems, including the Tecalemit-Jackson, faced significant challenges. The primary difficulty was the precise adjustment of the air-fuel mixture, which was often described as an "insuperable obstacle" without highly specialised equipment and expertise. These systems lacked the electronic sensors and feedback loops that modern EFI uses, meaning setup was a laborious, trial-and-error process requiring extensive bench testing. Furthermore, mechanical wear and tear could affect calibration over time, making consistent performance difficult to maintain. The reliance on precise manifold design for optimal performance also added a layer of complexity.

Conclusion

The 1967 Hillman Imp, particularly in its fuel-injected guises, was a true testament to British engineering ingenuity and a surprising powerhouse for its size. With figures reaching up to 130 bhp from a sub-litre engine, thanks to pioneering systems like Tecalemit-Jackson, the Imp transcended its economy car roots. These high-performance variants, whether factory prototypes or expertly tuned rally cars, demonstrated the transformative power of advanced fuel delivery. While early fuel injection systems were complex and challenging to master, their impact on the Imp's performance was undeniable, allowing it to compete, and often dominate, in a class far beyond its humble origins. The legacy of these mighty Imps continues to inspire, showcasing how a small car, with the right technology and a touch of daring, could achieve truly remarkable performance.

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