This article is reproduced from the June 1959 issue of Sporting Motorist.  You can download it as a PDF and view it in it’s original form.  Only some of the illustrations are reproduced below.  Thanks to Gary of http://frogeye.smugmug.com/ for this article


SportingMotorist0659.pdf


A MOTORIST has not to be particularly observant to appreciate that the Austin-Healey Sprite has become a fast seller in a short space of time. This applies to the North American and other export markets as well as to Britain. As we said at the time of its introduction , it meets a very real need among the sporting fraternity for it is of moderate first cost, its handling is excellent, and above all it is a safe small sports car. When Donald Healey conceived the car he had the younger driver in mind , particularly the young American . The car is so satisfying as a sporting machine, however, that its followers are now clearly in every motoring age and income group. For some of this extension of the Sprite's appeal we can probably give a good deal of credit to the performance-augmenting specialists-the Alexanders, the Yimkins, the Speedwells and others. All are unanimous that the little car is a particularly rewarding one on which to breathe their magic, for the basic design is sound all round and, in particular , the engine is a willing and robust one .

    Let us emphasise, however , that increasing performance has no magic about it, although we lightly used the word in the last paragraph . No specialist in this field can get ahead of the others because of knowledge they do not possess. Rather is it a matter of how the customer prefers to spend his money and whether he wants a car suitable for competition work- implying inferior retention of tune and a likely sacrifice of reliability-or merely more "steam" for better-than-ordinary motoring on 'the road . Sprite owners are well catered for in both respects.


The Manufacturers' Tuning

The entry of the manufacturers of the car into the field under discussion is significant, and a compliment to the sound work already done by others. The Austin Motor Company make it clear, however, that extra tuning invalidates their warranty where a new car is concerned. although they acknowledge that it will not "make the car hopelessly unreliable" . It should be at least as reliable as other cars of similar performance, they suggest ; and given sensible behaviour on the part of the driver and good maintenance. this has certainly been demonstrated by many Sprite owners. The Donald Healey Motor Co. Ltd. can carry out the work of modification and also list a variety of Sprite "mods" and additions, to which reference will be made later.

    The manufacturer 's policy in the matter of supertuning (to use their term) follows the successful pattern they instituted a good while ago for the M.G., i.e., several stages are suggested, and they sell such replacement parts as higher-compression pistons for reasonable sums. For the Sprite there are five stages of tune and the makers recently issued a booklet which briefly describes these. It will be helpful to the owner who is at least reasonably skilled with tools, reinforced by some mechanical knowledge

and experience. There are. of course, many keen owners who must feel that they cannot tackle such work with full confidence. To them, we recommend the services of a competent mechanic, a garage interested in tuning, or the Donald Healey organisation at the Cape, Warwick. The latter firm can , for example, modify and polish a Sprite head for £10.

    The Sprite engine has four cylinders of 62·9 mm. bore bv 76·2 mm. stroke and in standard form it produces 43 b.h.p. at 5,200 r. p.m. ; maximum torque is 52 lb. ft. at 3,300 r.p .m. Standard compression ratio is 8·3 to 1 and the unit has two H I S.U. semi downdraught carburettors, with GG needles. A Lucas 12-volt LA 12 coil is used with the same maker 's OM 2 PH 4 distributor; N5 Champion plugs are fitted.

    It will be of interest briefly to explain the various stages of tune which the Austin Motor Co. Lt d. have developed. They all have the merit of involving moderate outlay-if a fair amount of work with portable electric grinder and other tools .


First stage. It is pointed out by Austin that the combustion spaces should not be ground out as they are clean in standard form and partly machined. Light polishing all over and the removing of any " rags" that may be found will suffice. Any enlargement around the combustion walls may cause the cylinder head gasket to overlap and destroy the efficiency of the seal. The compression ratio will, of course, be lowered if grinding is carried out and the tuning thereby made partially ineffective.  Lightly grind and polish the exhaust and inlet ports throughout. They should not be ground out so heavily that the port shape or valve throat diameters are impaired. It is very desirable to match up , by grinding, the exhaust manifold ports with the cylinder head ports. Similarly, grind out and polish the inlet manifold, matching the carburettor bore; also make the bore of the manifold I 1/8in diameter at the cylinder head face by grinding out right through to this diameter. This work yields an increase of about 2 b.h.p,


Second stage. A further 2 b.h .p. (a t 5,500 r. p,m.) is obtainable by the fitting of flat-topped pistons (£9. 10s. on the home market) and resetting the ignition timing so that the point s break at 3 deg . before top dead centre; with the standard engine the static setting is 5 deg. before T.D.C.


Third stage. This is a more ambitious step in the work of raising power- up to 50 b.h.p . at 5,800 r .p.m, is reached when the following special parts have been fitted and the ignition retarded a further two degrees to I deg. B.T.D.C.

    Stronger valve spring s (15s. 4d. the set) are fitted and with these goes a higher-lift, altered-timing camshaft (£6). The valve timing which this gives is as follows , with the timing of the standard cam shaft in parentheses: Inlet valve : opens 16 deg . (5 deg.) before T. D.C., closes 56 deg. before T.D.C. (45 deg . after T.D.C.); exhaust valve: opens 51 deg. (40 deg .) before bottom D. e ., closes 21 deg . (10deg.) after T.D.C. Valve lift is 5 / 16 in ., or 7·94 mm ., with this special cam shaft ; with the standard one it is 0·28 in., or 7·14 mm.

    In place of the standard distributor a special one (£5 IOs.) is recommended with this camshaft ,and the GG needles in the S.U s. are changed to GM ones if the air cleaners are removed ; if they are retained, however, the needles a re not touch ed. Premium fuel of 93/97 octane must be used.


Fourth stage. A further 2 b.h.p. is obtain able after doing some work on the ports, this being shown in the accompanying sketches.
A sheet metal template should be carefully made to the dimensions shown in the upper sketch; and if this is attached to a long bolt it can be used conveniently as a gauge when carefully grinding out the neck of the inlet port at AA, as shown.

    Care is essential in grinding the inlet port throat to ensure that the enlarging is maintained absolutely central between the push rod hole s as the wall thickness left is no more than 86 thousandths (0.086 in .). The port should also be eased off as shown by the dotted lines in the sectional view through the inlet port. Easing of the valve guide boss as shown, and also easing the opposite port wall bend , will aid cylinder filling, but the work must be carried out with care.

    A somewhat similar treatment should then be given to the exhaust ports, the appropriate sketch showing how this should be done. With the se improvements the same carburettor needles as for condition No. 3 tuning are used and ignition timing is not altered.


Fifth stage. Some 2 to 3 b.h .p. (giving 54 / 55 b.h .p.) can be obtained (ac cord ing to the tune stage of the particular engine) by fitting the makers' own special tuned exhaust system. T his comprises a new front manifold , exhaust pipe, silencer and the necessary clips.


    If racing is in view

Particularly if the last stage of tune is used the Sprite owner may have competition work in mind. If sustained high speeds are likely to be indulged in it may be advisable to remove the engine cooling system's thermostat. An out let blanking sleeve can be supplied and this ensures maximum coolant flow at all times.

    The makers offer the timely ad vice of suggesting that

not only should tyres be looked at on a " hotter" Sprite

but wheel balance (static and dynamic) should be given

attention.

    Four alternative differential assemblies, including crown wheel and pinion to give different axle ratios, are available to the owner who wants best possible results. The standard assembly gives a ratio of 4·22 to I and the foIlowing can also be supplied : 3·727, 3,9, 4'555 and 5·375 to I.


Healey parts

As mentioned earlier ,the Healey works at Warwick are prepared to supply wire wheels and disc brakes for these cars, and although the outlay is naturally considerable it should be worthwhile for a car intended for competition work or for frequent Alpine pass motoring. They also do a wire-wheel conversion with retention of the original drum brakes; and they offer an attractive hardtop. There are also some less "performance" extras, the full list being as follows, with British retail prices.



Driving the Yimkin

by Jack Fairman

MANY firms do "Conversions" these days and in several cases it would appear that if money is no object then the sky can be the limit so far as sheer performance is concerned. But flexibility, reliability, and running costs can easily suffer. So I was interested to learn that Yimkin Engineering's idea of a Conversion on the Sprite costs only about half that of some others.

    Presumably anybody buying a Sprite is money conscious–otherwise he would buy a Jaguar-so the possibility of making a Sprite go a bit quicker without going bankrupt is of considerable interest.

    I drove the Yimkin Sprite to Silverstone and back, and found it a most pleasant and economical way of transporting two people and luggage. The engine, after being out all night, always started at the first touch on the button and the choke could be pushed back immediately . The car was extremely lively and it was difficult to appreciate that such performance could come from the same unit that propels the Morris Minor and Austin saloons. I expected any conversion to produce "side effects" such as pinking at low speeds or roughness, but the car could be driven like a small Town Carriage. I tried slowing to 1500 r.p.m. in top gear and found to my astonishment that the car would pull away smoothly and without pinking, even on a snap throttle opening. Once on the open road a comfortable cruising speed was around 70-75 m.p.h. Maximum speed on a nearly new and still very tight motor car seemed to be around 87-90 m.p.h.

    As the car is so small I was rather amused by the brake and gear levers which are on a scale more appropriate to a three ton truck. Again the steering was surprisingly heavy for a small car , but this again may have been due to its low mileage, and in any case may be a good thing at speed .

    One small criticism of the car–it is a pity that reverse is not on the other side of the box, as on changing from second to third it is far too easy to go right across the gate and snick reverse.

    However, full marks to all concerned. For a comparatively small outlay here is a car which goes, steers, stops, and corners, all in remarkable safety. Far better for the enthusiastic chap than spending the same amount on some doubtful heap or hybrid that is a short cut to the mortuary. Finally I did have time to take a few acceleration figures. Timed both ways over the same stretch of the Western Avenue and carrying two people and a full tank of petrol the results seemed to be slightly better than the Yimkin people claim for the car . Perhaps it is getting a little more run in now. In any case they would seem to be good value

for only £30.

0 to 50 m.p.h. 13· 1 secs.

0 to 60 m.p.h . 18·25 secs.

True speeds, not speedo readings.


Driving the Alexander

by Michael Christie

A SMALL sports car with the hood and sidescreens erected does not look its best, nor is it easy to get into. The Alexander Sprite, with its distinctive duoton flash along the body can truly (I hope) be said to look better than most, and the special door locks, featuring push button operation from the outside, do much to reduce the access problem to reasonable proportions.

    Once behind the wheel every thing feels well tailored and conveniently to hand. There is an initial tendency to push the dipswitch instead of the clutch, and bark the knuckles on the facia when changing gear, but one instinctively does neither after very short acquaintance.

    Similarly, on first acquaintance, response to the tiller feels most odd as the car oversteers on roll , but within an hour or so one simply does not notice this behaviour, and the faster it goes the better the car seems to handle.

    When pushed into a corner really fast the inside rear wheel lifts well off the road long before the car tries to break away, and provides a useful danger signal for the novice. Alexander have an anti-roll bar under development, which, by increasing the roll resistance at the front, tends to reduce the roll oversteer sensation, and the readiness to lift the inside rear wheel. When thoroughly proved in relation to the durability of the suspension, this useful accessory will be available through Alexander agents.

    In the power department, the difference between the Alexander Sprite and the standard model is quite remarkable, and one immediately looks for snags, on the assumption that such a difference must be obtained at the expense of low speed torque and tractability. The indisputable fact is, however , that nowhere throughout the r .p.m, range can one find a place where there is not appreciably more power than provided by the standard model. The idle is normal, throttle response is normal, fuel consumption is improved, and from being a 70 m.p.h. motorcar it now becomes a very willing 80 m.p.h, vehicle with a true maximum in the nineties. A road test by a contemporary magazine illustrates the potential of the car for competition purposes by obtaining a timed 100 m.p.h. with aero screen and tonneau cover. The long list of competition successes already garnered by normal Alexander Sprites is evidence of the suitability of this car for normal road use allied to a measure of club excitement at the weekends.

    Perhaps I can sum the Alexander Sprite up best by stating that in my experience it is the most reliable fun for the least money I have so far encountered, and reflect that when well-known figures in the motor industry repeatedly ask to borrow an Alexander Sprite for the weekend in preference to the vast array of potent machinery at their disposal, then we must assuredly have pulled something special out of the hat !


Development of the

Alexander Sprite

by E. C. Martin

Now that the Sprite has been with us for a year one can review its capabilities realistically, and even nostalgically, in the light of the many miles and late hours spent in its company!

    From early criticism of the handling and odd noises, the general feeling has swung to wholehearted acclaim for its ability to stay on the road and dispose of greatly increased horsepower without any ostentation whatever. To those old and tired in the business' of "extra steam" it is a most rewarding and dependable subject.

    The specification of the Sprite reached Alexander a short time before an actual car was available, and coupled with considerable experience on the 'A' series engine as converted for the A35 and Minor 1000, this information enabled the development department to get to work and have the basis of a Sprite conversion ready for road proving by the time a car had materialised. Despite this early start the Alexander Sprite conversion still reached the market several months after competitive conversions became available. This considerable period between prototype and production was accounted for by a most intensive programme of further development and durability tests covering the Swiss alps and the German autobahn. The result is a conversion which has given every satisfaction and accumulated an impressive list of competition successes. Not a single engine failure has been reported in six months

    Many people tend to assess the value of an added performance conversion by the number of horsepower added on paper and the degree of propulsion upon their hindquarters in the car. This is a fallacy. Given the necessary equipment and the time it is extremely easy to extract very considerable power increases from most modern engines, and many are the irresponsible ones who

gaily strive to this end! In fact, it is not at all easy to make an engine work appreciably harder without wrecking itself in a very short time, and the technical knowledge and experience required to arrive at the specification which produces a worthwhile power increase without sacrificing the durability of the engine is of a very high order: A moment of reflection should convince any logical person that this must be so. The car manufacturers employ some formidable brainpower in their research and design departments who arrive at the shape of an engine by the careful application of fact and logic. Each part is designed to withstand a specific maximum load, plus a margin of instantaneous overload, for safety. By utilising this overload capacity, more power can be obtained . But a crankshaft, like a piece of wire, can only be bent so many times before it fatigues and breaks.

    In the B.M.C. 'A' Series engine the first component to become critically overloaded as power is increased is, in fact, the crank shaft, and for the purposes of conversion development the maximum cylinder pressure and inertia loading are dictated by the beam strength of the crankshaft.

    Having determined the separate and combined limiting values in relation to all other forces affecting the crankshaft, the job of evolving a conversion for the Sprite engine presents itself simply as an endeavour to obtain the most suitable power curve possible without exceeding those values.

    Within this framework due regard must then be given to the cost of the conversion in relation to the first cost of the car, the cost per added horsepower and, most important, the cost of fitting and maintenance.

    Inertia loading increases as the square of the r.p.m., and maximum cylinder pressure soars as compression ratio is raised in return for a disproportionately small gain in m.e.p. The obvious course was therefore to keep the compression down in order to allow the use of r.p.m. to suit the gearing of the Sprite, and compromise in such a way that the peak of the power curve would coincide with its intersection with the resistance curve. An estimated power-curve / resistance-curve graph was made upon the basis of 9.4:1 compression ratio , twin H2 1 1/4" S.U. carburettors, 1 1/4 " dia. inlet valves and optimum manifolding, This would comfortably handle normal premium petrol without running-on and pinking and produce 52·5 b.h.p, at 5,800 r.p.m. for a true mean top speed of 91 m.p.h, in touring trim, with every promise that it would continue to do so for a normal life span.

    The necessary parts were duly made and development work on the airflow rig and dynamometer carried out. The final result was 55 b.h.p, at 6000 r.p .m. as the result of a slightly higher volumetric efficiency than anticipated.

    The final prototype conversion consisted of H2 carburettors on a flexibly mounted inlet manifold, flat top , solid skirt pistons, centre port exhaust conversion, and a large valve cylinder head giving 9·4: 1 compression. The shape of the curve, and the gear ratios, are such that it is not possible to overload the engine for more than a few seconds on the road.

    It is interesting to note that the particular engine had covered some 20000 miles in a Minor 1000 in Stage 1 tune before being detailed for Sprite development, whereupon it logged nearly one hundred hours on the dynamometer and fourteen thousand miles, to date , in the Sprite. In the course of further development on the road it was found desirable to increase valve crash r.p.m. by including slightly stronger valve springs in the conversion. This was dictated by the considerable gap between third and top gears, and since the shape of the power curve protects the total loading situation it was permissible to allow 7000 r.p.m, in the intermediate gears .

    Tests with thermometers in various places under the bonnet revealed that a discrepancy between dynamometer performance and the true top speed of the car, was due to an unusually high carburettor air temperature. An air pressure box with pressure balancing to the float chambers, and a cold air intake from the front of the car, was therefore evolved which restored the full power of the engine plus a further half horsepower at maximum speed. The difference in installed engine horsepower with and without the air box is as high as ten percent, which makes it a well worthwhile investment.

    Having made a car go faster, one must also make it stop with equal willingness, and after due investigation it was found that the main criticism with the existing brakes was the very high pedal effort required. The fitting of anti-fade linings aggravated this problem, but they did provide adequate braking performance for fast road drivfqg. It then remained to adapt the Alexander power brake unit to the Sprite to relieve the driver's leg, and a quite reasonable braking performance emerged with sufficient 'feel' to allow accurate heel and toe downshift during maximum retardation.

    As the road-proving miles passed month by month with no snags, and as the car reappeared at the works after a thorough work out at the hands of various road test authorities without any signs of ill humour, it became evident that the Sprite was a- worthy subject for the full Alexander treatment. This would enable the purchaser to obtain his new Sprite complete with all modifications on the same terms as any other new car, and covered by the comprehensive Alexander guarantee.

    To those already operating a standard Sprite, the engine conversion alone must have considerable appeal. For seventy two pounds one receives the necessary parts to add some fifteen propshaft horsepower, as well as a virtually reconditioned engine. Reports from users indicate that fuel consumption is materially improved regardless of how the car is driven, and it seems that the newly-converted are highly delighted with the results .

    Since the very nature of the Sprite made it obvious that it was destined for the circuits in considerable numbers, the development department, having finalised the road conversion, was given the further job of evolving equipment for racing performance. The requirements for this purpose are fundamentally that the engine should produce the highest possible useful power for sufficient time to practise and finish the race. It was therefore felt that a full power-life of three hours would be a reasonable basis for development, and parts were designed accordingly. It is worth mentioning that the part-throttle life at normal r.p.m. would be no different from any good road engine. A good racing engine is not a good road engine, however, as it will not creep willingly in traffic and makes great demands on the patience. It is in fact a useless piece of machinery other than for racing, or full throttle operation,

since the considerable power has to be obtained at the expense of nearly every other attribute of the well-behaved

engine.

    By addition or substitution a special long dwell camshaft, lighter pistons, a further modified head and valve gear, H4 1 1/2" carburettors, and a more efficient exhaust system were combined with the basic road conversion to produce 68 b.h.p . at 6800 r.p .m. on 100 octane petrol with a 10-8: 1 compression ratio. Valve crash occurred at 7,400 r.p.m. The engine in this form proved to be reasonably tractable and if necessary could be driven to events. The fuel system was fairly conventional, and apart from the addition of an oil cooler and tuned exhaust system the installation was normal.

    One can be fairly certain of one thing in the preparation of racing machinery, however, and that is that if impressive results are obtained quickly and easily, they will very quickly cease to be impressive. What one can do, another can do equally well. Put it another way: to pass another Sprite at walking pace when both are flat-out requires a horsepower differential of at least 6 b.h.p. Since one races to win or not at all from the business and advertising point of view, the issue then arose of evolving a special head to provide this advantage. Various preparatory steps were taken towards the evolution of such a head , but owing to the pressure of other conversion work the project was shelved. Meanwhile Geoff Williamson, of Ford overhead inlet fame, pressed on with a special 'A' series head and with the prototype casting, which, allied with home brewed carburettors, quickly approached the best figures obtained with a modified iron head.

    It is hoped to provide a detailed description of the Alexander alloy head and accessories at a later date , by which time the full potential of this very promising piece of equipment will have been demonstrated on the circuits.


 

June 1959