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Pitman's Motorists' Library
"The Book of the Morris Minor 1000 (All models to 1960)" by Staton AbbeyCHAPTER XI
TUNING AND MODIFICATION
[Engine Tuning] [Supercharging] [Raising Rear Axle Ratio] [Chassis Modifications]
[Modified Minor Club] [Suppliers of Special Equipment]
It is an encouraging thought that at a time when manufacturers of popular cars are forced by economic conditions to adopt an increasing degree of standardization, enthusiastic owners are still prepared to spend a moderate amount of money, and sometimes a considerable amount of time, to ensure that their cars have a better performance and still better handling qualities than unmodified models from the same production line. If proof were needed, one could point to the steadily increasing interest in "do-it-yourself" tuning and modification kits for popular cars, which has become evident in almost every country of the world.
Part of the explanation lies in the fact that the engine of the modern "family" type of car possesses considerable reserves of stamina - its power output can be increased quite appreciably, without risk of unduly shortening its life or incurring other expensive consequences. In this respect the B.M.C. "A" type engine fitted to the Minor 1000 is no exception to the general rule.
As installed in the Minor, for example, it develops a maximum power of 37 b.h.p. at 5,500 r.p.m., whereas the same engine in more highly tuned form in the Austin-Healey Sprite develops 43 b.h.p. This little power unit can, in fact, be developed to give over 50 per cent more power than in the standard form, without sacrificing reliability, easy starting and tractability.
Engine tuning is, of course, too complex a subject to be dealt with in any detail in a short chapter. An owner who proposes to carry out such work may find of interest a specialized book on the subject. Pitman's Engine Tuning for the Owner-Driver. The less experienced owner, on the other hand, need not be debarred from improving the performance and handling qualities of his car, since his needs are well catered for by specialist firms that produce bolt-on engine tuning and suspension modification kits which are supplied either on an exchange basis, or which can be fitted either by the manufacturer of the kit or, in some cases, by local distributors. Road testing and final adjustments are then carried out by skilled mechanics. The addresses of some of the firms specializing in modifications for the Minor are given at the end of this chapter.
It should, perhaps, be made clear at this stage that the appeal of these modifications is not restricted to owners who are anxious to try their hands at trials, rallies or club racing, although modified Minors have acquitted themselves well in such events. One of the chief attractions of a moderately-tuned Minor is that it puts in the hands of a family driver a small, comfortable car, compact enough to fit into the modern pattern of congested traffic, with inherently good road manners but now possessing a very lively performance that enables it to hold its own with cars of up to twice its engine capacity and of far higher price, even when allowance is made for the cost of tuning.
Engine Tuning.In conventional tuning, modifications are made to the induction system, cylinder head and valve gear that aim at improving the "breathing" of the engine - that is, its ability to draw in an adequate amount of air at high speeds, when the restriction caused by the standard carburettor, induction system and valve gear limits the maximum power that can be developed.
The most usual modification, therefore, is to substitute a twin-carburettor inlet manifold for the single-carburettor layout. The increased flow of gas through the engine then calls for an improved exhaust manifold and, preferably, a straight-through type of silencer. The reduction in exhaust gas back-pressure will not only enable the maximum performance to be obtained, but will also tend to prevent any possible overheating and will improve the petrol consumption.
When the engine is tuned to this extent, the maximum revolutions obtainable in the gears will be limited by valve bounce - that is to say, the valve springs will no longer be able to keep the valves and tappets in contact with the cams. When this happens the valves tend to remain open and the engine speed is automatically limited. The fitting of stronger valve springs overcomes this difficulty and also improves the life of the valves and seatings. In the latter respect, however, there is a good deal to be said for fitting better-grade valves than the standard parts if the engine is likely to be driven hard.
In addition to ensuring adequate filling at high speeds it is usual to carry out a fair amount of work on the cylinder head, both to ensure that the volumes of the individual combustion chambers are matched as closely as possible — an ideal that cannot be expected in the standard engine, owing to the limitations of mass-production casting techniques — and also to raise the compression ratio to a moderate extent, in order to extract a greater amount of heat energy from the burning charge. The standard ratio of 8.3:1 can safely be increased to 8.7:1 - a ratio as high as 9:1 has, in fact, been used without rendering the engine rough or lacking in flexibility at low speeds, although super-premium fuels must be used if pinking is to be avoided.
Before leaving the subject of conventional tuning, it should be mentioned that probably the least expensive way of obtaining a really substantial improvement in engine torque (pulling power) and smoothness, combined with reduced fuel consumption, is to fit a G.M. Modifier between the carburettor and the standard inlet manifold in order to re-atomize the globules of petrol that condense on the carburettor throttle plate, ensuring much more even fuel distribution. Two modifiers can be fitted when a twin-carburettor layout is used. While a single modifier, fitted at the carburettor flange, will give excellent results the principle can be taken a step further by substituting a Mangoletsi-modified inlet manifold for the standard article. These manifolds, which are obtainable on an exchange basis from the G.M. Carburettor Co., have a G.M. modifier fitted permanently at each flange that mates with the inlet passages in the cylinder head and also at the carburettor flange. The induction passages are polished where necessary. Owners have reported that the fitting of one of these manifolds, retaining the standard single carburettor, has given results that are closely comparable with those obtained from some twin-carburettor modification sets.
Supercharging.An entirely different approach to the problem of increasing the output of the engine is to draw the mixture from the carburettor through a belt-driven supercharger and to feed it under pressure to the cylinders, thus ensuring that a full charge is drawn in under all normal running conditions, plus about one-third of the nominal capacity of each cylinder when the engine is operating at full power. For this reason a supercharger can also be used to compensate for the inevitable loss of power that is experienced when an engine operates at high altitudes and is drawing in air of reduced density.
Except when used for racing, most supercharger installations are of the low-pressure type: that is to say, the "boost" does not exceed 2-8 lb/sq. in., which is unlikely to overstress any modern engine in the family-car class. This type of supercharger usually gives smoother running since besides packing more mixture into the cylinders, it also compensates for some of the deficiencies of mass-produced induction systems.
Modern superchargers are virtually trouble-free. They are lubricated automatically from the engine and are quiet in operation, apart from a slight whine which is evident with some types while accelerating but which disappears when the throttle is eased back. It is essential, however, to obtain the advice of a specialist before deciding on a suitable type and to consult your insurance company regarding a possible increase in premium - some companies do not view superchargers too kindly and impose a rather heavy loading on the policy.
In any event, before deciding on the most suitable method of increasing engine power output it is advisable to write to the specialist firms listed on pages 123-4 - these will provide a great deal of information, including, in many cases, reprints of reports of road tests of modified cars carried out by the leading motoring journals. One is thus able to study comparative specifications, performance figures and costs.
Raising Rear Axle Ratio.When the engine has been tuned and normal driving conditions entail a fairly high proportion of fast main-road cruising, it is worthwhile considering raising the rear axle ratio from 4.5:1 to 4.2:1. The higher ratio will reduce the engine revolutions throughout the speed range, resulting in a lower noise level in the car. reduced "fussiness" at high speeds and improved fuel consumption. The maximum speed will be slightly reduced but acceleration is not noticeably affected.
Sets of higher-ratio gears, complete with a recalibrated speedometer, can be supplied, and fitted if required, by tuning specialists.
Chassis Modifications.As has been stressed elsewhere in this book, the Minor has excellent handling characteristics and providing that it is not driven to the limit of its performance, a tuned example will probably need no further modification. If full advantage is taken of the increased power available, however, two modifications are well worthwhile. The first is an anti-roll bar, which is quite easily fitted to the front suspension and brings about a marked reduction in roll when cornering fast. It also improves tyre adhesion.
The second is a modification to the rear suspension designed to reduce or eliminate rear wheel "skip" or "tramp", which occurs when the full power of a modified engine is transmitted through the lower gears while accelerating away from a standstill. The modifications offered by specialist firms to cure this trouble fall into two categories: locating the rear axle by means of torque arms, and the substitution of telescopic shock absorbers for the standard type. In most cases the latter can be mounted without the need for further modification. The particular scheme recommended by the B.M.C. Competition Department, however, calls for vertical mounting of the dampers, when it is necessary to cut into the boot and to weld in a sheet-metal box on each side to provide upper fixing points. A racing or trials enthusiast would consider the work involved (and the restriction of the space in the boot) justified by the efficiency of this particular modification, but one of the less elaborate schemes will probably satisfy the average owner. Fig.48. The Speedwell Gran Tourismo suspension conversion for the Minor 1000 Finally, we come to the all-important subject of brakes. Again, for normal driving the standard system will probably prove entirely adequate but if the brakes are used frequently at high speeds they may show a tendency to "fade" when they become overheated — that is, pedal travel will increase and efficiency will fall off — although normal braking will be restored when the shoes and drums have been allowed to cool. Specialist tuning firms can supply "hard" linings which give consistent braking but — as is usual in such cases — these have a lower coefficient of friction than the standard linings and call for a correspondingly heavier pressure on the brake pedal to produce a given braking power. This drawback can in turn be overcome by installing a brake "booster" in the hydraulic circuit - here again the tuning specialist can offer equipment that can be fitted with the minimum of trouble.
Modified Minor Club. Before leaving the subject of modifications it may be mentioned that owners of modified cars and those who are contemplating tuning and other alterations can make contact with fellow enthusiasts through the medium of the Modified Minor Club. The address of the Secretary is 9 Blakesley Avenue, Ealing, W.5. (remember, this is the address from 1960, you'd be better to contact the MMOC)
A member who requires details of a particular modification is put in touch with another who has already carried it out. In addition, a great deal of first-hand practical experience is, of course, exchanged during discussions at club meetings.
SUPPLIERS OF SPECIAL EQUIPMENT(remember, these are addresses as they were in 1960, they may not still exist!)
Engine Conversions and Tuning Kits:Alexander Engineering Co., Ltd., Thorne Road, Haddenham, Bucks.
Aquaplane Co., Ltd., Oulton Broad, Suffolk.
V. W. Derrington, Ltd., 159-161 London Road, Kingston-on- Thames, Surrey.
Downton Engineering Works, Ltd., Headlands, Downton, Wilts.
Palace Gate Garage, 50 Queens Gate Mews, London, S.W.7.
Performance Equipment Co., Tower Building, Liverpool, 3.
Speedwell Performance Conversions, Ltd., 763 Finchley Road, London, N.W.11.
Induction Manifold Modifiers:G.M. Carburettor Co., Ltd., Cranford Works, Malt Street, Knutsford, Cheshire.
Performance Testing Meter:Bowser, Monks & Whitehouse, Ltd., Doncaster.
Superchargers:Carburettors, Ltd., Grange Road, Willesden Green, London, N.W.10.
North Down Engineering Co., Westway, Caterham, Surrey.
Shorrock Superchargers, Ltd., Empress Works, Walsall Road, Willenhall, Staffs.
Suspension Conversions:Postland Engineering & Trading Co., Ltd., Crowland, Nr. Peterborough, Northants.
Palace Gate Garage, 50 Queens Gate Mews, London, S.W.7.
Speedwell Performance Conversions, Ltd., 763 Finchley Road, London, N.W.11.
Transmission Modifications:Alexander Engineering Co., Ltd., Thome Road, Haddenham, Bucks.,
and most of the other firms listed above under Engine Conversions and Tuning Kits.
Of course any companies or products mentioned in the text may not exist today and any prices listed are of course no longer valid, so take company and product refernces with a grain of salt.
If anyone has a problem with copyright then please contact me.page_textpage_textpage_text
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