A 100 m.p.h. Imp—from Rootes

EIGHT dedicated people under the supervision of Des O’Dell at Rootes Competition Department in Coventry currently have the most frustrating jobs in the improved performance business, for they have proved their workshops can prepare cars to beat the world and yet, because of a high-level Rootes decision to withdraw from competition, they can no longer demonstrate the point to a motoring world which needs as many different marques as possible. After a brilliant, if lucky, Marathon victory and countless televised rallycrosses, reaching audiences of approximately five million, in which Andrew Cowan and Peter Harper defeated the traditional Goliaths with the baby Imp, it was especially sad that the company should choose to stop entering works cars. Happily, it has been decided that the competition workshops should remain in action to produce road and competition performance equipment. If this move is profitable, then at least we can hope to see the Pentastar restored with full works participation at time controls and starting grids throughout the country.

The Imp which is the subject of this MOTOR SPORT road test was prepared by Rootes’ competition section to conform with Appendix J, Group 6 Prototype regulations issued by the FIA. Yet it was all a tuned car should be; perfectly happy either to poodle along at 2.000 r.p.m. in top gear or to react as a soul-shattering and competitive sports machine capable of acquitting itself honourably in all forms of loose surface motorsport. ALN 650H was designed specifically to take part in rallies, as it was built up from a new body shell for the 1969 International Scottish event, although not used for the purpose.

However, when the news of the company’s competition decision reached the workshops it was seen that this Imp could act as a mobile unit to demonstrate the goods available to the public, for with three exceptions (which we shall detail shortly) all of the equipment is on general retail sale through the department or Rootes dealers.

O’Dell is the manager of the department while Ridgeway acts as the link between customers and the men producing the equipment. The two of them described every detail of the car’s specification to us. However this would run into two pages of text by itself, so below is a brief summary.

The engine is developed from the 875-c.c. Imp Sport unit which produces just over 50 gross b.h.p. In Group 6 guise the capacity is increased to 998 c.c. by enlarging the block and inserting cast iron cylinder liners: power output increases to 100 b.h.p. gross or 94 nett at 7,200 r.p.m. The Imp engine has never been noted for torque, but in this form it is fairly generously endowed with 74 lb. ft. at 6,500 revolutions. The cylinder head is extensively modified with larger (1.375 in.) inlet valves, enlarged porting, reshaped combustion chambers and slightly machined face increasing the compression from 10 to 10.4 to 1. The single overhead camshaft is reprofiled to conform to the R17 specification increasing valve lift to 0.36 in. Exhaust valves are standard, as is the crankshaft, though the latter is balanced in conjunction with its fellow moving parts and strengthened by the tuftriding process to increase life.

Externally we could see the rear radiator cowling and fan had been removed, larger pullies fitted to the water pump and alternator (a non-standard Lucas 11AC), plus one-piece inlet exhaust manifolding upon which a pair of twin choke side-draught Weber carburetters are installed; a conventional 9-gill oil-cooler replaces the standard “wire brush” unit.

The most useful improvements in other areas are not yet freely available. They are: front disc brakes using Viva discs and Girling racing alloy calipers, front-mounted radiator connected to the rear by one-inch-bore aluminium tubing plus good stout hosepipe, and a meticulously constructed 10 gallon fuel tank. The tank itself forms part of the front construction of the car. Other more easily obtained improvements are the redesigned interior with two exceptionally comfortable reclining seats (using the old Alpine frames) and matt black padded dash panel incorporating a clear (though inaccurate) speedometer, amperemeter, water temperature and fuel gauges, a 10,000 r.p.m. Smith’s tachometer on top of the panel, considerably stiffened, and strengthened suspension utilising RAC coil springs and adjustable Armstrong AT9 shock-absorbers, 6-in. wide rim Minilite road wheels with low profile 12-in. diameter “chunky” tread Dunlop radial tyres, competition steel ringed rubber driveshaft couplings, low ratio third and fourth gears (m.p.h. per 1,000 r.p.m. is approximately 14.1 in top gear) full harness Britax seat belts and lighting guaranteed to melt the paint on the boot lids of dawdlers in the outside lane.

However, it is really the bodywork which confines this saloon to the prototype category, for Perspex side and rear windows are used and the rear seat is removed. The resultant expanse of metal is neatly carpeted and a spare wheel installed in the centre, glassfibre panels substituted for the standard steel bonnet and engine cover and two scoops installed on the rear to feed air to the carburetters (which are protected by an adapted Sunbeam Tiger air cleaner) and the oil-cooler. The heater is pretty well gutted, so the Triplex electrically-heated front window is useful on rainy or cold days.

This constitutes a long list of modifications by anyone’s standards and it’s one which brings the Imp’s asking price up to £1,500 or so: including the £450 expended on the engine. Is it all worth it? Yes, if you are a keen driver who enjoys having even a small amount of skill amply repaid by startling cross country averages covered in complete safety. The Imp is also beautifully engineered and immaculately finished so that just to explore some of the static features could satisfy a stringent connoisseur.

In approximately 1,000 miles of tarmac and loose surface use we found only minor points at which to carp, while the effortless but exhilarating handling, coupled with vice-free retardation and acceleration which is fantastic by 1,000-c.c. saloon car standards, is more than compensation for these. No fan is fitted to either radiator, but in spite of this we never boiled the coolant, even when trapped for 10 minute periods by London traffic. After such a delay the application of full throttle would produce a misfire around 6,000 r.p.m., but this could readily be cured by blipping the tachometer to its given limit of 8,000 revolutions. The factory informed us that 9,500 r.p.m. has been used for short periods without disaster, but we refrained from using more than 8,600 as an absolute limit for acceleration runs. This must be one of the few cars MOTOR SPORT has tried which pulls in excess of 8,000 r.p.m. in top gear under favourable conditions. The most we could accurately record in terms of top speed was close to 105 m.p.h., however, so we are forced to the conclusion that the tachometer was as inaccurate as the water temperature gauge and speedometer: in fairness we must point out the speedometer drive could not be recalibrated to cope with the low profile tyres.

The modified suspension provided a stiff, but not a jarring ride on main and country roads, though really to appreciate it one has to find unmade roads. On such terrain, the car rides superbly and flies through the air as though Imps were designed primarily as wingless aircraft.

Handling is superb on any surface, the large leather-rim steering wheel requiring only minimal effort, even when changing from lock to lock at low speed. Initial understeer gives way to a long period of neutral handling during which hard acceleration will cause the inside front wheel to lift long before the rear loses adhesion. The absolute road-holding limit is unbelievably reassuring and if the car were to be fitted with similar section read tyres, as opposed to the test car’s “chunkies”, it would take a fool or a very skilled driver to induce any breakaway at either end. Driving on slippery roads is great fun as the rear conveys plenty of warning before it starts to swing wide.

The rear mounted engine and efficient suspension allow one to release the clutch at 7,500 r.p.m. from a standstill, and accelerating away with little wheelspin. However, the engine location does not aid the Imp’s stability in a crosswind, so that in this respect it is much like the standard product, excepting high speeds (90 plus m.p.h.) when it is far more controllable than the standard product. In the author’s experience this crosswind behaviour is alarming only on first acquaintance, for as with a VW, one soon instinctively applies the necessary steering corrections.

During our week of ownership the Imp started easily, required none of the recommended Shell M engine oil and consumed five-star fuel at the rate of 22 m.p.g. The main snag is the noise level which is not surprising when you consider 56.4 m.p.h. in 4th gear represents 4,000 r.p.m., our legal limit just over 5,000 r.p.m., and nearly 85 m.p.h. in the same ratio is equivalent to 6,000 r.p.m. We tended to cruise at a still higher speed as our ears became accustomed to the din and our senses awakened by the vibrationless manner in which the engine operated throughout the r.p.m. range.

What a shame it is that the works cannot once again offer a genuine Sunbeam, equipping (say) the Stiletto with a 1,300-c.c. engine, but in the meantime enthusiasts for the Imp marque can console themselves with the endless permutations offered be the 1-litre engine right up to the stage we have described.—J.W.