Tuned Car Test

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The Talbot Sunbeam Cheetah

Stag Hill Motors’ 2-litre fireball

With a mechanical recipe incorporating the best aspects which have made Avengers consistently competitive in rallying for many years, the Talbot (nee Chrysler) Sunbeam should be a natural basis for performance tuning. Talbot themselves have recognised the fact with the ultimate option, a 150 b.h.p., 16-valve, 12-litre Lotus engine mounted in this compact hatchback. But this exciting little package has been so long emerging from its gestation period that we began to wonder whether it would ever see the strip lights of a dealer’s showroom. By the time this story appears in print we should have driven one and some of you might own one, but that doesn’t invalidate the raison d’etre of the Talbot Sunbeam Cheetah, an astounding bullet of a motor car offered as a much cheaper alternative to the Lotus Sunbeam by Surrey Chrysler dealers Stag Hill Motors. 0-60 m.p.h. in about seven seconds, a top speed of around 112-118 m.p.h. depending upon which of two final drive ratios is chosen, overall performance and exciting handling which stirred our adrenalin more than any tuned road car for many a long day and an all-in price of around £5,500, considerably cheaper than the projected Lotus price, make the little Cheetah something of an enthusiast’s dream.

Stag Hill Motors proprietor Paul Burch, a typical amateur enthusiast in driving tests, club rallies and so on, is responsible for this volatile package, which is put together for him by Dawson Auto Developments at Milton Keynes. The Cheetah starts life as a brand-new Sunbeam 1.6GLS with 80 b.h.p., but after Andy Dawson’s ministrations boasts 2-litres and around 145 b.h.p.

The kernel is the so-called “Brazilian” cylinder block, manufactured in South America for a 1.8-litre Dodge equivalent of the Avenger. This block is taller than the British 1.6-litre item, allowing the use of a 77.19 mm stroke crankshaft instead of the 66.67 mm standard stroke. Dawson bores the block out to 90 mm and fits Avenger Group 1 pistons to achieve a capacity of 1,964 c.c. The reciprocating parts are balanced to competition standard. There is nothing new about this recipe, which has been in regular and very reliable use in rallying for some years, and indeed Dawson continues to build the blocks for rally Avengers and Sunbeams.

The Cheetah’s cylinder head is retained from the original 1.6-litre engine, but is extensively modified, with 1.65 in. inlet valves, 1.42 in. exhaust valves and opened out ports. A Talbot Group 1 camshaft is fitted and the oil pump is uprated. Carburation is by twin 40DCOE Webers, which have smaller chokes than the normal Group 1 specification to give better bottom end tractability. The test car’s Webers were mounted on a Janspeed combined inlet manifold and free-flow exhaust manifold. Since then Dawson has changed the specification to separated manifolds to avoid heat soak from the exhaust to the carburetters when the engine is ticking over in town traffic conditions. The exhaust system is a pukka Talbot Group 2 rally system.

Such drastic engine modifications have necessitated many other improvements along the line. A competition clutch is fitted (a little “soft” on the test car), and to ensure that all the power isn’t lost through wheelspin (112 b.h.p. at the wheels has been shown on a rolling road) a limited slip differential with a 60 lb. ft. pre-load setting is fitted in the live rear axle. The modified suspension specification includes uprated front struts with a high leak setting, 100 lb. per inch front springs, hard rubber bushes, Armstrong adjustable rear shock-absorbers and lowered Sunbeam rear springs. The test car had 185/70 x 13 in. Pirelli CN36 tyres fitted to the same attractive 6 in. wide alloy wheels upon which the Sunbeam Lotus was first announced; I understand that production Lotuses will use different wheels. The wheels are a part of the Cheetah package, but since my test Dawson has changed the tyre specification to 175/70 in the interest of easier handling and is experimenting too with 50 per cent profile Pirelli P6 tyres on 14 in. wheels.

“Cheetah” badges on the flanks, nose, tail and instrument panel identify this Stag Hill Motors special — but the trumpeting of the Webers underbonnet and the virile rasp of the exhaust spells out the message even more effectively! The engine is a little screamer, all the way up to its 6,500 r.p.m. maximum — 700 r.p.m. beyond peak power — and wound up thus the performance is electrifying. Most astonishing of all is the top gear performance, which would have Ferrari Boxer and Porsche Turbo owners weeping into their beer. Supercar performance would take over beyond 100 m.p.h. or so as the Cheetah reached the limits of its power curve. It finally runs out of steam in top at 6,300 r.p.m., 112 m.p.h. on the test car’s standard 3.7:1 final drive ratio. Apparently the Cheetah will pull exactly the same revs in top on the optional 3.54:1 final drive, equating to 118 m.p.h. Most Cheetah customers are sacrificing a little bit of acceleration for the easier and quieter cruising afforded by the higher ratio.

The test car’s light gearchange was sweetness itself, but the ratios were too wide to encourage deliberate tune playing. Though the ratios are not ideal, the Cheetah’s torque of 120 lb. ft. at 3,800 r.p.m. (the torque curve is almost flat from 3,000 r.p.m. to 5.300 r.p.m.) glosses over this drawback, as the performance shows.

This is definitely not a car for novices. It needs an expert touch to control handling which can bite very viciously indeed if the short wheelbase Cheetah is not treated with respect. In wet conditions especially the transition from understeer to oversteer is about the quickest I have experienced and needs catching instantly. The throttle needs treating circumspectly in such conditions. It would be much more forgiving without the limited slip differential, but would be desperately short of traction too. I musn’t give the impression that the Cheetah handles badly: driven skilfully with proper regard to the 145 b.h.p. underfoot in 17 cwt, the 96 in. wheelbase and the limited slip differential with high pre-load, this is a fabulously rewarding car to drive and quite indecently quick. I haven’t driven an example with the narrower tyres, but Dawson tells me that so equipped the Cheetah is more forgiving and easier to handle.

The big tyres were partly responsible for a rear damping problem on the test car, which was afflicted with a choppy, bouncy ride. Not only was this uncomfortable and tended to throw the car around over bumps, it also created a conflict of frequencies between the rear dampers, the seat cushion and the driver’s right foot on the sensitive throttle, making it very difficult to hold a steady throttle setting on bumpy roads. Dawson claims to have ironed out this damper problem on production Cheetahs.

The brakes were so good I assumed Dawson had fitted bigger discs, remembering that the performance of the standard Sunbeam’s “anchors” is nothing out of the ordinary. In fact all he does is to substitute Ferodo DS11 competition brake pads on the standard Sunbeam 9 1/2 in front discs. The rear drum brakes are left alone.

In spite of its high state of tune by road car standards the Cheetah is tractable enough and never protested via its temperature gauge or plugs in heavy London traffic, through which instant performance and compact size enabled it to slice like magic. Town driving had its embarrassing side, though; because the differential was set up with that very high pre-load it grumbled and groaned and griped when turning out of road junctions or manoeuvring. Passers-by looked sympathetically at the sufferer of mechanical disaster. The noise is perfectly normal, of course, and can be expected to quieten a little as the differential settles down with a few thousand miles under its belt.

Consumption of four-star very much depends on the driver’s enthusiasm; driven very hard, using all the revs, the Cheetah will return only 19 m.p.g., but most owners, once the novelty of the performance has been accepted and style tempered, should manage 24-25 m.p.g.

The Cheetah is supplied with the standard Sunbeam-steering wheel and seat, the latter too short in the cushion and ineffectual in support for the cornering forces promotable, both items inappropriate for this high-performance car. A good bucket seat and smaller, leather-rimmed wheel should be essential, but Paul Burch feels, sensibly, that by leaving them out of the Cheetah package the customer is free to make his own choice as to type.

The more I drove this remarkable little “bomb” and came to terms with its characteristics the more I enjoyed it. The Cheetah is not an easy car to drive and is certainly not a reward to give your I7-year-old son for passing his driving test, but in the right hands it is tremendous fun. Performance against pound it is excellent value for money and an ideal, versatile tool for the local motor club competitor. Indeed, the weekend before the car was delivered into my hands Paul Burch had won a driving test with it, proof of the pudding. – C.R.

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