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Cary Grant admiring an early Hillman Imp. This innocuous little car sported a miniature Coventry Climax engine located behind the rear axle. Photo graciously provided by The Imp Club U.K. Click here for a better view.
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Poor Man's Porsche, English Style, by Allan V.
Lacki. Creative automotive
design flourished in the late 1950s and early 1960s, especially in the U.K.
Most auto enthusiasts are aware of the transverse-engine front wheel drive
Austin Mini, designed by Alec Issigonis. The Mini's basic power train layout,
so brilliant because of its compact packaging, continues to serve as the
blueprint for almost every passenger car in production today. However, the
Mini was not the only small British sedan worthy of our interest. The U.K. also
produced its own "Poor Man's Porsche".
At the same time that Chevrolet was developing prototypes for the Corvair, the
Rootes Group in England was designing a smaller but similar rear engine economy
car, the Hillman Imp. Development of the Imp began in 1955, but production did
not start until 1963, three years after the Corvair was introduced. The Imp
remained in the Rootes lineup until 1976.
Head-on, the Imp looks like a miniature early-series Corvair. The resemblance
is more than coincidental. While Rootes stylists were borrowing contours from
the Corvair body, Rootes engineers were test-driving Corvairs, looking for
technical solutions to rear engine design problems. Unlike their counterparts
in the styling department, the engineers didn't copy the Corvair so readily.
After crashing one 'Vair rather severely at the test track, Rootes rejected
swing axles and adopted a fully articulated multi-link rear suspension for the
Imp. And, to minimize rearward weight bias, the Rootes engineering staff
insisted on a lightweight all-aluminum engine.
And what an engine it was! For the basic layout, Rootes engineers called upon
Coventry Climax, one of the most renowned engine designers in the world.
Coventry Climax engines powered some of that period's most successful Formula 1
cars, including the Lotus 18 and the Cooper T51. Coventry Climax was eager to
capitalize on its racing success and sold Rootes the production rights to a
state of the art overhead cam 750 cc four cylinder engine. Rootes proceeded to
modify the design to make it suitable for the Imp by opening it up to 875 cc,
laying it over on a 45 degree angle, increasing the compression ratio to 10:1,
and die-casting the block and head in aluminum.
One of the problems of an aluminum block is that, without steel liners, cylinder
bores are subject to premature wear. However, the process of pressing steel
cylinder liners into an aluminum block represents a considerable manufacturing
expense. Like the engineers who developed the Corvair engine, Rootes almost
specified a hard high-silicon alloy to negate the need for liners. However,
again like their counterparts at GM, Rootes found that it could not master the
technique of machining this unproven material.
Rather than give up, Rootes chose another alternative, opting for an aluminum
block with iron liners cast in-situ, just like Buick's 1961 aluminum V-8. The
quest for weight reduction paid off. The finished engine weighed just 170
pounds, "including accessories."
The little Climax engine was water-cooled, so the engineers positioned the
radiator alongside the engine behind the rear seat. This solution, common to
the Fiat 600, Simca 1000, Renault R8, and a number of other European rear engine
cars, compromised cooling efficiency but avoided the need to mount the radiator
in the front luggage compartment. This simplified the plumbing and provided a
modest boost in luggage space.
Like most innovative cars, Imps gained a reputation for teething problems.
Rootes worked hard to correct these problems, but most consumers in the English
economy car market took the conservative approach and selected Brand X instead.
Over thirteen years of production, about 500,000 Imps were sold.
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Sports car enthusiasts, however, recognized that the Imp offered great driving fun at reasonable cost. The Coventry Climax engine was smooth and could be revved with confidence up to 7,000 rpm. English car magazines raved about the Imp's excellent handling, which apparently was as good as the Austin Mini's. All over the Isles, enthusiasts entered Imps in club events for many years. Two specialty manufacturers, Ginetta and Clan, produced hand-built sports cars based on Imp components, quite similar to the Corvair-based Fitch Phoenix in concept.
If you would like to read more about the Hillman Imp, there are a number of web-sites that will satisfy your interest, including "The Imp Site", which through the courtesy of Franka Steenhuis, served as the source for much of the information in this article.