Tuning topics

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An honourable turn of speed from 998cc

In the May issue we struck our first official acquaintance with Datsun’s smallest offering in the UK, the 1-litre Cherry 100A. Although this Japanese machine is often compared to the Mini because of its transverse engine and f.w.d.—plus sundry other design similarities within the engines themselves—such talk is really rather wide off the mark, for the small Datsun is fully comparable with cars in the European 1300 class. In fact the car represents a very clever cross between the performance of many 1300s (better in some cases), overall fuel consumption not far short of the 850 Mini (in enthusiast hands) and carrying capacity for passengers and luggage that makes the Mini look like a shoe box.

Acknowledging that the Datsun Cherry is a Good Idea is one thing— improving on the oriental theme is another, as we discovered when talking to Janos Odor about the project. Mr. Odor, through his specialist motor engineering works in Salisbury, has developed a wide range of slightly off-beat machinery in the past 12 months or so. Long famous for quicker BL racing Minis and manifolding of high repute, Janspeed have spent those months on such diverse projects as the Hillman Avenger the author raced in handicap events last year: on twin Weber carburetters it could return lap times that compared well with respectable sporting machinery, a point that the factory noted when planning a true Group 1 car that has now materialised as an extremely potent machine in the hands of Bernard Unett. The Hillman Avenger Tiger also shares many of the features that Janspeed had incorporated on their Avenger, which was not only raced but served honourably as a shopping tool for Mrs. Odor and general press demonstrator. Possibly it was the success of this project that convinced the company to spread their wings ever wider and subsequent projects have included two Cortina Mk. 3s currently doing the press rounds and serving Janspeed in between times; a Morris Marina 1.8, which went well, but only did one press road test as the company were not proud of its manners; the Toledo we tested in colour last year and a variety of pure racing projects which include a Buick/Oldsmobile/Rover alloy V8-engined Capri built on a shoestring and a Group 1 Ford Escort Sport that has currently scored six class wins, and holds four class records.

When work started on the Datsun engine, Janspeed found it very intriguing to deal with; it’s certainly theoretically similar to the legendary BMC-developed A series engine that finds its way into everything from Minis to Marinas, but there are manufacturing refinements that make the practical end result superior. The three bearing crankshaft is part of heavily oversquare interior dimensions; the bore is 73 mm. and the stroke just 59 mm. If that suggests that the unit will rev. willingly for you, then pat yourself on the back, for high r.p.m. for astonishing lengths of time are part of the Cherry character, particularly on the modified model. Although the cylinder head is made from aluminium, unlike the BL unit in iron, there are similarities in the porting and combustion chambers that make life easier for those brought up on improving British Leyland engine power outputs; incidentally, both manifolding for the exhaust and carburation is on the same side, closest to the driver.

Janspeed charge £28 for the modified cylinder head on exchange, for which the customer receives a head with ground-out and polished porting, double valve springs, enlarged combustion chambers and 25 thousandths of an inch machined from the cylinder head face. The latter pair of machining and enlarging operations counteract each with regard to their effects on compression ratio, which remains similar to the production figure of 9.0-to-1.

The standard Hitachi twin-choke compound carburetter was dispensed with in favour of that traditional Mini pick-me-up, a pair of 1 1/4-in. choke HS2 SU carburetters costing £26.50. One unusual feature on the test car was that the dashpot air-hole was also dispensed with in an experimental move to see if throttle response could be made any faster. “Go-faster” pancake air filters are disliked by Mr. Odor for the noise they emit under hard acceleration, but on this first installation of SUs for the Cherry there seemed little alternative; the filters are priced at £2.80.

Inlet and exhaust manifolding are all in tubular steel by the converters. The exhaust layout follows a four into two branch and single pipe configuration, priced at £15.00. The quadruple inlet stubs were provisionally priced at £12, but it will not be long before cast alloy inlets are available for the Datsun from Janspeed. The remainder of the exhaust system has a larger bore, up by 1/4-in. throughout for £12.

That completes the engine modifications on the test car, except to say that part of the cylinder head conversion is to lighten the production valves, so that the valve gear loads are kept down, whilst liberal use of the 7,000 r.p.m. provided is made.

Suspension and gearing characteristics had both been changed by the adoption of 13 in. diameter 5 1/2-in. rim alloy wheels from Mill Accessory Group, deputising for the showroom, gaudily decorated, (with fake Porsche “spoke” hub caps) pressed steel wheels, which are 12 in. diameter, 4 1/2. in. rim. Naturally the rubberwear had to be swopped as well, radial ply Firestone Wide Ovals of 165/70 HR construction sitting in under the modified bodywork with vestigial spats. It’s a reflection of the current emphasis on wheel and tyre equipment that Janspeed should expand nearly £110 retail on just these items. The suspension, which is all independent by MacPherson struts up front and semi-trailing arms aft, was very much stiffer in action than standard, utilising Koni damping at all four corners as well.

Finishing touches include a servo for the very effective brakes and a Smiths electronic tachometer, which slips neatly into the space provided on the production dashboard.

Looking at the Cherry before we slithered away from a damp Salisbury, we were irnpressed with the enormous track that the car has on these bigger wheels: judged by eye one would opine that the little Janspeed machine had the track of a Cortina-sized vehicle, but in reality—even with the wider wheels—the track can be little more than 4 1/2 ft.; the overall length is 11 ft. 10 in.

The engine started readily enough, despite the choke’s apparent inability to pull out to full effectiveness. Thus the petrol/air mixture would be a little lean for the first moments of running after a cold start. Luckily Datsun fit an electric fan as standard equipment, so the power unit very swiftly warmed to work after a suburban start: country dwellers must sit in the garage, or imagine there are sets of red traffic lights every 200 yards or so!

Really any description of the engine performance is superfluous, for by the standard of engine size and the way in which it was designed along old principles, the Janspeed Datsun unit is extraordinarily near perfection. The low final drive (4.286:1) and modest degree of tune ensure that the Cherry remains superbly flexible whilst packing an overtaking punch that is astonishing to all but hardened Mini-Cooper S owners. Jan Odor remarked before we left that the car feels very much faster than it actually is, which puts one in mind of a small buzz box straight away. However, the sensations that the driver receives are far more akin to the smoothness a Honda motorcycle owner feels whilst exploring the nether regions beyond 10,000 r.p.m. You can tell that the little engine is working hard to pull just under 13 cwt. of best Rising Sun Cherry along, but the driver is not tormented with demented screams from engine and transmission, or vibration periods akin to Mount Vesuvius in full eruption. Instead one gazes with mistrust, for hours on end if need be, at the tachometer reading between 6,500 and 7,000 r.p.m. as the Datsun skims along between 90 and 100 m.p.h. As a motoring experience this Janspeed modified Cherry certainly qualifies as something new and the only similar car we can recall, though it was far more sophisticated in its engineering approach and revved a little higher with less torque, was the Honda S800 sports car. The modified Hillman Imp 1-litre engine is very similar as well, but the Datsun achieves a similar smoothness whilst mounting the engine at the front, which must prove something about the effectiveness of the original soundproofing and conversion.

The only fly in the ointment is a small period of harshness that vibrates the rear view mirror at 6-6,200 r.p.m., approximately 85-90 m.p.h. true speed in top gear. When you are winding the engine up the r.p.m. scale in the gears this period is unnoticed, but it is a cruising speed to be avoided by comparison with the comfortable hum below and above this point in fourth.

To analyse the car’s potential a little more fully than usual we took the Cherry to Silverstone, where the smiling staff partook lightly of our cash in exchange for a little impromptu drag racing and a spell exploring the machine’s capabilities around the Club circuit layout. The reason for the latter exercise (apart from the joy of unpoliced motoring) was merely to establish if the Cherry on road tyres would be any match for the racing tyre-shod Moskoviches that dominate the cheapest class in Group 1. Under the present price regulations the Cherry would not stand a chance, but if the price bracket were upped next year in deference to the cost of living rises, then the Datsun at £660 basic, just under 800 retail, might possibly find a competitive niche somewhere. The times the car recorded were excellent by the cheapest Group 1 class standards and it would be a reasonable choice in the next most expensive class as well! Now we know that Group 1 doesn’t permit the changes made on this car, but it is a fact that the difference between a showroom Capri and the one you see sliding round a circuit in a Britax or Castrol Group 1 event is about 10 seconds a lap, thanks to racing tyres, suspension changes like those featured on this car, and whatever “blueprinting” the RAC scrutineer feels like allowing at that time of the month!

The handling is naturally dominated by degrees of understeer, a condition which can be cancelled by untidy mid-corner braking or lifting off the throttle. In the wet the Cherry tended to run wide excessively, but as soon as the driver takes a feel of f.w.d. techniques there are few problems to rapid and entertaining transport. In fact two very important aides to the modified Cherry’s cross-country speed are the properly made production seats and the brakes, which will pull the car up in under 30 ft. from 30 m.p.h. without the generously proportioned wheels and tyres ever locking up. The major snag to this sporting suspension was the degree of stiffness with which the system was arranged for spirited demonstration runs. Whilst this feature suited the car perfectly on a race track, it would be important for potential customers to consult with the converters before having precisely the same modifications. Those who are used to taking their families for quiet country lane runs might well have a mutiny their hands if the test suspension was slavishly copied!

Straightline performance figures are given in the data panel as usual, but for those who like to take a perspective on things we would add that this simple conversion takes the Cherry into the performance range occupied by 998 Mini Coopers (which you cannot buy nowadays of course, the rough and frequently slower 1275 GT having taken over that niche with benefits primarily to driver and passenger comforts) the converted Imp range with 998 c.c. engines, production 1275 c.c. twin carburetter models from British Leyland, and the Radbourne Fiat 127 tested briefly last month. Compared to the production Cherry, Janspeed’s modifications have cut the 0-60 m.p.h. times by just over 3 seconds and 0-80 by around 16 seconds, which is really rather clever. Top speed of the standard Cherry is 2-3 m.p.h. short of 90 m.p.h.; under favourable conditions we could comfortably exceed 90 m.p.h and our two-way average worked out at 101 m.p.h.

Considering that the Salisbury company have had the car for such a short time (it had only 1,300 miles or so on when we picked it up; we managed just over 1,100 miles according to the odometer, but that was as innaccurate as the speedometer because of the wheel and tyre changes) the writer felt that the Datsun represented a terrific “first-off” conversion and extraordinary value by anyone’s standards. Fuel consumption remained entirely reasonable at 33.7 m.p.g. overall and oil consumption was just one pint after 600 miles had been covered at very high engine r.p.m. The only trouble we had with the car was a need to top up the brake fluid on the second day of our week loan period. Thereafter no further fluid was needed, so somebody must have miscalculated after the servo was fitted. Well done, Janspeed! Doesn’t it make a patriotic heart shrink to think what potential there must be left in the Cherry, if this is just the tip of the iceberg ? — J. W.

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