Hillman Imp

Which classics still have the potential to get up and go? Steve Rowe remembers the cars, the tuners, the people, and tells you why they’re still hot

With the Mini Cooper celebrating its 50th this year, it’s too easy to overlook it’s main UK rival, made from Scotland. We’re talking about the Imp of course, the other mini that deserved far greater respect and success than it got during its unhappy 13 year run. Despite poor build quality, the Imp was actually very innovative, with a rear mounted aluminium engine mounted plus independent suspension all round. It even featured an early version of the hatchback body style that is so popular today. Performance versions of the Imp soon gained success in motorsport, particularly in rallying, with the company even producing a tuned version called the Hillman Rallye Imp. As with the Mini, badge engineering was also a feature of the Imp story, with versions badged with the Sunbeam and Singer names. Perhaps most attractive of all were the coupe versions, badged as the Imp Californian Coupe, Singer Chamois Coupe and Sunbeam Stiletto. And best of all, you can still hot them up

Get One Now

Imps are a lot rarer than Minis so the search is harder, not helped by the fact that the standard of cars out there is pretty average – a result of the lowly values. You can buy a very good Imp for less than a couple of grand and perhaps £3000 and a bit for a peach; they’re so inexpensive that you’re better buying the best you can rather restore a wreck, which should cost no more than £500 tops. Don’t expect to pay much on top for a Stiletto or Imp Sport but the Husky vans can command a premium due to their rarity. Early Imps could be chronically bad in terms of reliability but MK2s and later were better. Naturally rust is always the biggest concern of course but they fare no worse than the BMC rival and parts supply isn’t bad either. Engines and transaxles always need a watch; the former known for overheating, for example. If you’re upping the performance of your Imp, it also worth checking the condition of the brakes and transmission. In particular, make sure the Rotofl ex rubber doughnuts on the drive shafts are still in sound condition. These act as universal joints on the driveshafts and they will eventually wear and can tear away from their bolt sleeves.

Hotting One Up

The engine wasn’t of Hillman’s design but sourced down the road. The Coventry Climax unit was primarily designed as a standing water pump, favoured by the Fire Brigade because it could be taken to max revs from cold. It was also used in the Lotus Elite and some of Jack Brabham’s conversions, such as the Herald. With an advanced aluminium overhead cam 875cc engine the fi rst models off the production line back in 1963 produced just 39bhp at 5000rpm. Keen to promote a more spor ting image, Rootes soon introduced some performance models. The factory modifi cations still used the 875cc block but replaced the single Solex carburettor with two Stromberg CD125 carburettors.

Other changes included a hotter head, cam and exhaust. All this added up to a useful power increase to 51bhp at 6100rpm.  Models fi tted with this more powerful engine included the Sunbeam Imp Sport, Sunbeam Sport, Singer Chamois Sport and Stiletto. The ultimate factory performance version was the Hillman Rallye Imp. This used a 998cc wet-liner engine, with a bigger bore (72.5mm) and twin Stromberg 150CD carbs for 65bhp at 6200rpm. It’s still one of the best engines (especially if taken further to 1040cc). The maximum speed was now 92mph, compared to just 74mph for the most basic of the original 875cc cars. It stands to reason that the fi rst step is to up the engine to Sport tune, which was on par with a Mini Cooper; it could be all you need for the road. We spoke to Dennis Alt, a Hertfordshire based Imp tuning specialist Transimp (Tel: 01442 217610) who explained that most of the work he does consists of upgrading engines to the 998cc wet liner unit, as used in the factory Rallye Imps. At one time you could buy the 998cc block off the shelf from a main dealer. Now, the 875cc engines are bored out and wet liners are added to either 930 or 998cc. Dennis had some of these wet liners remanufactured and has since sold over 800. The best head to use is from the Spor t model and these have an oil drain on the back. These heads can normally be identifi ed with casting numbers that ended in 180. The head from the MK2s also had an oil drain hole.

The bottom of the engine is normally okay in standard form, until power gets above about 80bhp, when it may be worth fi tting tougher crank and bearings. Dennis also says that it’s important not to use split-link chains as these aren’t tough enough. Dennis tends to stick with carbs, since most of the engines he builds are for Historic Touring Cars. Some Imp owners fi t the 930cc engine from the Talbot Sunbeam, which used a modifi ed Imp casting with a stiffer block and can be tuned-up like the other engines. It’s not a straight swap but not diffi cult either.

For a more basic upgrade on a standard 875, some owners fi t twin or twin choke carburettors. Together with an improved inlet and exhaust manifold (try Janspeed) on a polished head, this can increase the performance and add another fi ve of so bhp.The next stage is to fi t larger inlet valves. At the same time, the camshaft should be upgraded to a performance version – Sport spec is the minimum. Other Imp tuners include Corley Conversions and Mark Maynard (01453 833185) and you can always contact the owners club on 01494 531966 http://www.theimpclub.co.uk. Mark says 90bhp is a good fi gure to call ita day for the road as the transmission is weak if you go further. He produces an inlet/exhaust manifold to accept Weber DCOEs which work okay on the road and advises fi tting the uprated radiator he makes costing £100. Most alien engine swaps (Ford crossfl ow etc) don’t work that well, he warns.