Sunbeam Stiletto

Rootes Group

Industry	Automotive
Founded	1913 (1913)
Founder	William Rootes
Fate	Acquired by Chrysler Europe in 1967
Headquarters	Coventry , United Kingdom
Products	Automobiles (including Hillman Imp)

The Hillman Imp represents a compact economy car manufactured initially by the Rootes Group and subsequently by Chrysler Europe between 1963 and 1976. Introduced to the market on 3 May 1963, it was distinguished as the first British mass-produced vehicle to feature an aluminium engine block alongside an aluminium cylinder head.

Conceived by designers Michael Parkes and Tim Fry under Rootes’ direction, production took place at the Linwood facility in Scotland. The lineup encompassed the Hillman saloon, the estate Husky, a panel van variant, and a coupé model.

The Imp garnered moderate acclaim within club-level and international rally competitions. In 1964, Rootes launched a homologation special known as the Rally Imp, equipped with an enlarged 998 cc engine. This particular version notably achieved both first and second positions at the 1965 Tulip Rally.

Despite its forward-thinking engineering, the Imp suffered from reliability problems that adversely affected its reputation in the marketplace. These difficulties played a role in Rootes Group being acquired by Chrysler Europe in 1967. Manufacturing persisted until March 1976, with total sales approaching half a million units over the course of thirteen years.

Development

Internally designated as the APEX project within Rootes Group, the Imp’s development was driven by the fuel shortages resulting from the 1956 Suez Crisis. With petrol rationing impacting the UK and diminishing demand for Rootes’ larger automobiles, there emerged a rising interest in small, fuel-efficient cars. The BMC Mini had already established a strong presence since its production launch in 1959. Although officially initiated in 1955, the project rapidly transformed into Rootes’ inaugural compact economy car.

Engineers Mike Parkes and Tim Fry proposed the design concept, which received approval from Rootes’ engineering director B. B. Winter. Initial concepts such as "The Slug," which bore resemblance to bubble cars, were dismissed by Rootes’ board in favor of a more conventional design. Comprehensive testing occurred across varied environments including Norway, East Africa, and Arctic Canada under Ken Sharpe’s supervision.

Prior attempts by Rootes to develop small cars included prototypes like the 1938–1939 Little Jim and the post-war 1949 Little Jimmy; however, these projects had minimal influence on the Imp’s final design.

The Imp utilized a 742cc engine inspired by the Coventry Climax FWMA design, initially planned to be available in three displacements: 800cc, 875cc, and 998cc. Due to high engineering expenses, increased vehicle weight, and reliability concerns associated with experimental 998cc dry-liner engines, only the 875cc variant was adopted for production. This decision restricted the Imp to a single engine size, unlike competitors such as the Mini offering multiple options. A taller engine block allowing for a longer stroke was evaluated but considered too costly unless sales justified development. Some long-stroke engines were produced and subsequently bored out to 1150cc for competition purposes by racers including Paul Emery and Andy Dawson.

Later iterations of the 998cc engines fitted to Rallye Imps employed costly wet liners and were primarily designed for racing rather than everyday driving. It was eventually determined that the maximum reliable displacement achievable from the 875cc engine was approximately 948cc; nevertheless, neither this nor a proposed 928cc version—intended for a Mark III Imp—entered production due to Chrysler’s budget reductions. The concept behind the 928cc engine resurfaced years later in the Chrysler Sunbeam.

Mark I Imp: 1963–1965

The Hillman Imp was introduced on 2 May 1963, with the Linwood factory officially opened by HRH the Duke of Edinburgh. One of the earliest models is preserved at the Glasgow Museum of Transport, while a 1963 example is on display at the National Motor Museum, Beaulieu.

Before and after its debut, the Imp garnered significant attention from automotive journalists. In 1962, Small Car & Mini Owner drew attention to its all-aluminium water-cooled rear engine. The Daily Express described it as "the first baby car ever built by the Rootes Group". By June 1963, Motor Sport commended its engine, transmission, and competitive pricing—£508 for the standard version and £532 for the deluxe.

The "Imp" designation was obtained from Ailsa Craig Ltd., a marine engine manufacturer, in a trade deal with Rootes Group involving a new Humber Super Snipe. The name highlighted the vehicle’s small dimensions and positioned it as a direct rival to the Mini.

The sophisticated water-cooled four-cylinder engine utilized an all-aluminium overhead camshaft and a fully synchromesh aluminium transaxle—features uncommon in small cars of that era. Sir Alec Issigonis, designer of the Mini, had previously considered full synchromesh "impossible". The engine was inclined at 45° to lower the center of gravity and enhance handling characteristics.

To counteract typical oversteer associated with rear-engine layouts, the Imp incorporated a semi-trailing arm independent rear suspension—a complex and expensive setup inspired by testing on a Chevrolet Corvair. Initially, front suspension used swing axle geometry that caused understeer; this was addressed by lowering pivot points to reduce camber.

UK sales increased from around 33,000 units in 1963 to 50,142 in 1964, but dropped to 42,663 in 1965 due to reliability problems related to inadequate rear engine cooling. This negatively impacted customer confidence during a crucial phase when Rootes aimed to challenge the Mini’s market dominance, which saw over 1.19 million units produced throughout the 1960s.

The Mark I model was launched as a two-door saloon available in Basic and De Luxe specifications. In October 1964, a premium Singer Chamois variant was introduced.

Mark II Imp: 1965–1968

Addressing early shortcomings of the Mark I, Rootes Group reintroduced the Imp with significant mechanical and aesthetic improvements. The Mk II replaced the pneumatic throttle linkage and automatic choke with more conventional systems and refined front suspension geometry. Additional upgrades included a new water pump, cylinder head featuring larger ports and valves, and 'Mark II' badges on the doors. These enhancements improved reliability and driving performance, although no single modification matched the comprehensive nature of the 1965 redesign.

Mark III Imp: 1968–1976

After Rootes Group was acquired by Chrysler Europe in 1968, the Imp lineup underwent further updates—excluding the Stiletto variant. Changes involved redesigned instrument clusters and steering wheels; the large central speedometer was swapped for a horizontal array of four round gauges customized for each model. Control stalks were consolidated into one multi-function stalk positioned on the right side of the steering column. Although these revisions aligned with efforts to streamline production, some critics felt that the new dashboard missed an opportunity compared to the original’s well-regarded ergonomic design.

Rootes, Chrysler, and Production Conclusion

Early reliability problems significantly damaged the Imp’s market image, with half of its total output produced within the initial three years. Although it offered competitive pricing, distinctive design, and economical operation, sales did not meet projections. Limited familiarity with alloy engine upkeep among owners and dealers contributed to mechanical issues, compounded by frequent failures of the Giubo coupling. The Mini ultimately surpassed the Imp in consumer preference.

The considerable financial commitment made by Rootes to develop the Imp and establish the Linwood facility played a role in the company’s fiscal difficulties. While labor disputes and complications arising from its alliance and subsequent takeover by Chrysler USA were major contributors, the Imp’s disappointing sales further deepened financial losses. After Lord William Rootes passed in 1964, Chrysler assumed full ownership by 1967. Despite inflationary pressures, most Imp variants saw price reductions domestically in 1968.

Chrysler's leadership is frequently identified as a key element in the decision to cease Imp production in March 1976, after manufacturing fewer than 441,000 vehicles. The entire Chrysler Europe division faced ongoing challenges and was eventually acquired by Peugeot two years later. The Imp stood as one of the United Kingdom’s longest-produced automobiles, with a manufacturing run spanning 13 years. Its replacement within Chrysler UK’s range was the Chrysler Sunbeam—a three-door hatchback built on a rear-wheel-drive Avenger platform—also assembled at Linwood until the plant closed in 1981 after 18 years of operation.

The Ryton factory continued operations until December 2006, when Peugeot relocated production of the 206 model to Slovakia.

Design

As a direct rival to the BMC’s Mini, the Imp utilized a compact rear-engine, rear-wheel-drive configuration to optimize both passenger accommodation and luggage capacity. It featured an innovative rear hatch that opened for loading luggage through the back seat backrest.

This model was Britain’s first mass-produced car equipped with a rear-mounted engine and also pioneered the use of a diaphragm spring clutch. Its baulk-ring synchromesh transaxle managed synchronization between gear and shaft speeds prior to engagement, resolving early transmission issues similar to those experienced by the Mini.

Distinctive elements included a folding rear bench seat, an automatic choke—a feature rare outside North America until the 1970s—and instrumentation for temperature, voltage, and oil pressure, whereas many contemporaries replaced such gauges with warning lights.

The overhead camshaft engine design provided superior airflow compared to typical OHV engines and was straightforward to enhance for increased performance through upgraded silencers and carburettors. However, Rootes’ modifications for large-scale manufacturing rendered the engine less robust than its Coventry Climax predecessor. The Imp’s powerplant was derived from the Climax FWMA series but differed from the FWMC engine used in Lotus vehicles.

Marketing

Initially, Rootes marketed the Imp as a premium second family car offering features above standard expectations. Subsequently, its positioning shifted toward an ultra-budget vehicle with simplified components, drawing comparisons to Eastern European economy cars such as those produced by Škoda and Lada. At one stage, the Hillman Imp held the distinction of being Britain’s most affordable new automobile, temporarily increasing sales figures.

Variants and Badge Engineering

Throughout the Imp's production run, Rootes (later Chrysler UK) offered four distinct body styles. The initial saloon, produced from 1963 to 1976, was notable for its opening rear window and fold-flat rear seats—features uncommon in compact cars at the time—that improved access to the luggage area. In 1965, a "Commer Imp" van variant was launched. Two years later, in 1967, the coupe version named the Imp Californian was introduced alongside an estate model called the Hillman Husky, which utilized van body panels but featured unique styling cues. Both the van and estate models were discontinued in 1970.

To increase market penetration amid sales figures significantly below the target of 100,000 units annually, Rootes expanded the lineup with badge-engineered versions such as the upscale Singer Chamois (introduced in 1964) and the sportier Sunbeam Sport (released in 1966) equipped with twin-carburettor engines. For export markets, Singer-branded cars were frequently marketed under the Sunbeam name; however, after May 1970, Chrysler UK phased out the Singer brand entirely. In countries like France, all Rootes vehicles—including the Imp and Husky—were sold under the Sunbeam badge.

The coupe shared much of its design with the standard saloon but featured a lower-profile windscreen and a fixed rear window. Although presented with a more dynamic appearance at the 1967 Paris Motor Show as the Sunbeam Stiletto, this model did not deliver enhanced performance compared to the saloon, whose aerodynamics were marginally better. The coupe body style was also applied to less powerful Hillman Imp Californian editions and higher-specification Singer Chamois variants.

Manufacturing

The introduction of the Imp marked a major and expensive strategic pivot for Rootes, which had limited recent experience producing small vehicles despite initially entering that segment with the Hillman Minx back in 1931. By the time of the Imp’s debut, the Minx had transitioned into a mid-sized family car. Rootes became a pioneer in mass-producing an aluminium engine for this model—a sophisticated undertaking necessitating construction of a new computer-controlled assembly plant located in Linwood, Paisley. This facility was developed with financial support from UK Government Regional Assistance grants aimed at generating approximately 6,000 jobs in a region suffering from shipbuilding industry decline. The Linwood plant housed an advanced die-casting operation for aluminium engine blocks and held a stake in a newly established Pressed Steel Company factory responsible for manufacturing body panels.

Linwood’s geographic position created logistical complexities: aluminium engine castings were transported roughly 300 miles south to Ryton for machining and assembly before being returned north to Linwood for final installation into vehicles—a round trip of about 600 miles coordinated through scheduled rail services that moved components and finished cars efficiently. To optimize logistics further, Linwood also produced body pressings for the Hillman Avenger model that were shipped south to Ryton. This operational pattern continued throughout Linwood’s period of Imp production.

The workforce recruited mainly from shipbuilding backgrounds generally lacked specialized skills in automobile assembly, contributing to challenges with product quality and reliability. Additionally, industrial relations issues—including frequent labor disputes and strikes—were common during this era within British manufacturing sectors and adversely affected production continuity.

In total, close to half a million Imps were manufactured, with approximately fifty percent produced during the initial three years.

Overseas Assembly

Complete knock-down (CKD) kits were exported for assembly in various countries including Australia, Costa Rica, Ireland, Malaysia, Malta, New Zealand, Philippines, Portugal, South Africa, Uruguay, and Venezuela. In New Zealand, Todd Motors assembled Hillman vehicles from around 1964 until 1970 when Imp production ceased to focus on Hillman Avenger manufacturing instead. Todd Motors operated two final assembly lines at Petone: one dedicated to both Avenger and Hunter models; another for Chrysler Valiant production.

Rootes Australia commenced assembly of Imps at its Port Melbourne facility starting in 1964 with several variants:

• PM Imp: Offered only in standard trim (1964–1965), assembled from UK Mk I CKD kits. The Super Imp variant was introduced in 1965 featuring enhancements later incorporated into the IMP II.
• PA Imp ("IMP II"): Available in standard or Super trim between February 1966 and March 1968; still based on UK Mk I CKD kits.
• PB Imp ("IMP III"): Produced from 1968 until approximately 1970 in standard or Super trims; initially utilized UK Mk I CKD kits before transitioning to Mk II kits and engines for later batches. Some final units may have employed solely CKD Imp Sport body shells.
• Hillman GT: Manufactured from Sunbeam Imp Sport CKD kits between 1967 and 1968.
• Hillman Sonic/Stiletto: A convertible model assembled by Eiffel Tower Motors of Dandenong under contract for Chrysler Australia.

These variations illustrate Rootes’ approach to tailoring the Imp platform for regional markets while managing local manufacturing constraints.

Variants

• Hillman Imp Mark I (1963–1965)
• Hillman Imp de Luxe Mark I and II (1963–1968)
• Hillman Super Imp (1965–1974)
• Hillman Imp (1968–1976)
• Hillman GT (1967–?), developed by Chrysler Australia based on the Singer Chamois Sport; never officially marketed as "Hillman Imp GT"
• Hillman Imp Californian (1967–1970), available as coupé and fastback saloon
• Hillman Husky (1967–1970), estate model
• Commer Imp Van (1965–1968)
• Hillman Imp Van (1968–1970)
• Hillman Imp Caledonian (1975–1976), limited edition (~2,000 units) in Cherry Red with additional features, offered in Super and De Luxe trims
• Singer Chamois Mark I & II (1964–1970)
• Singer Chamois Rallye (1965–1968), rally variant with an enhanced 998cc engine and upscale appointments
• Singer Chamois Sport and Coupé (1967–1970)
• Sunbeam Imp Sport (1966–1970)
• Sunbeam Sport (1970–1976)
• Sunbeam Chamois (export markets outside the UK)
• Sunbeam Stiletto (1967–1972)
• Sunbeam Californian
• Sunbeam Imp Basic and De Luxe Mark I & II (North American market)

Vehicles utilizing Imp components

• Beach Mk4
• Bond 875 and its versions
• BS Nymph
• Clan Crusader
• Concept Centaur GT
• Davrian
• Ginetta Cars G15
• Siva Llama

Between August 12 and 14, 1964, the Sunbeam Imp sports sedan (ZT-86-20) achieved a new "world record" for a transcontinental endurance drive across the United States, surpassing the previous 53.5-hour benchmark set by Erwin George “Cannonball” Baker in 1933. Covering 3,011 miles from New York City to Los Angeles in 48 hours, 9 minutes, and 54 seconds, it maintained an average velocity of 63.7 mph.

The Imp gained significant recognition in motorsport when Rosemary Smith triumphed at the 1965 Tulip Rally, inspiring Rootes Group to offer a specialized rally conversion named the Imp Rallye under both Hillman and Singer badges. Although the car faced a disputed disqualification in 1966 after winning the Coupe des Dames, it continued to be a formidable contender. In touring car competitions, Bill McGovern secured three consecutive British Saloon Car Championship titles from 1970 through 1972 driving a Bevan-prepared Sunbeam Imp, despite minimal factory backing.

Within UK club racing circuits, multiple Imp variants demonstrated dominance in the under-1000 cc Special Saloon class, driven by notable racers such as Ian Forrest, Harry Simpson, Ricky Gauld, John Homewood, Roger Nathan, Gerry Birrell, Ray Payne, and Chris Barter. These vehicles still participate actively in historic rally events like the HRCR Clubmans Rally Championship.

Globally, the Imp also enjoyed success in Asian saloon car racing throughout the 1980s with drivers including Andrew Bryson and Pardaman Singh. The 998 cc engine powered numerous three-wheeled racing sidecars during the 1970s and 1980s, frequently fitted with Twin Weber twin-choke carburetors. Several teams competed at the Isle of Man TT sidecar races; notably, Roy Hanks finished eleventh in the 1976 TT 1000cc Sidecar event. Sidecars equipped with Imp engines remain competitive in vintage sidecar racing contests.

In hydroplane competitions, Andy Chesman claimed the 1972 World Hydroplane championship utilizing a modified Imp engine. After acquiring Greetham Engineering—specialists in Imp tuning—Chesman developed a wedge-shaped cylinder head that boosted output to 125 bhp from a 1220 cc displacement with twin Weber 40DCOE carburetors. During BP’s Windermere records week in October 1972, he established a class water speed record of 89 mph which stood until his passing in 1998.

Additional resources

• Morgan, Tim (May 2017). Hillman Imp: The Essential Buyers Guide. Veloce Publishing.

External links

• The history of the Imp
• The Imp Club official site
• Information on the Hillman Imp and related badge-engineered models
• Andy's Hillman Imp website — dedicated to Hillman Imps and their engine variants
• The impact of Margaret Thatcher's policies on the closure of the Linwood factory — marking the 50th anniversary of the Imp and Linwood’s shutdown