HOW TO BUILD YOUR OWN CAR
WHA T is a ” Special ” A
” Special ” is a car built by an amateur, either entirely to his own design, or by combining the essential parts of a number of makes. There are two kinds of” Special” : the out-and-out racer, and the “road car.” I am going to concentrate rather on the racing side, because I have had most experience of that, and your secretary wants_ MC to wax reminiscent.
What is the object of building a “Special ” ? Because you can’t afford to buy a car to give you the characteristics you require. It is most unlikely that the impecunious an iateur, working in his spare time, will M any way compare with works jobs, but some astonishing things. have happened.
How to set about building a ” Special.”
In getting down to the general layout, a little elementary mathematics will avoid a lot of useless effort and disappointment. Much work has been Wasted on ears fundamentally incapable of giving the required performance. In order to have some sort of ” mental yardstick ” of performance, try to find out the exact details of the b.h.p., weight, frontal area, etc., of as many cars as possible, so as to have a fairly (‘lose estimate of what the proposed device will, or will not, do. It sounds a hit or miss method, but is actually more accurate than any of these formulte, in which you seem to be able to make your motor-car go as fast as you like, on paper, by ” mucking about ” with the constant ” K.”
Design. Detailed drawings should be made of the complete car, and of every individual part. Work out from these if there are any impossible assemblies or inaccessible parts normally requiring servicing. To take an extreme instance, it is undesirable to be compelled to remove the engine from the chassis in order to clean a plug. Design is conditioned by the facilities which are available, and by the amount of tune which 37011 CU11 spend on the job. If you have the use of all sorts of elaborate John Bolster’s talk, lecture, paper, opus, or what have you, was so very well received by everyone present that I deem ” Motor Sport “fortunate indeed
to be able to publish it.—Ed.
workshop equipment, go right ahead with all the most advanced ideas. If you haven’t, getting work ” done out ” will cost a fortune, so you must curb your enthusiasm. It is sometimes possible, by the use of unconventional methods of fabrication (e.g., welding, brazing), to avoid a lot of expensive and accurate machining (e.g., splines). I )on’t be downhearted if your facilities are very meagre. I took a number of course records and “fastest times of day ” with a car which
had a wooden chassis frame (like the Mosquito !).
A most important point is ease of servicing. A really ” hot ” motor will require a great deal of dismantling and titivating between cacti event, and anything very complicated will be too much for the single-handed owner-desiglierdriver. I have found that one’s driving ability just goes to blazes if one has to work too late every night before racing, and that’s a thing I have suffered from very much since making my 4-litre job. However ‘carefully prepared, the car needs a lot of work between practice laps and racing next day, alas !
Cost. After careful study of the design, make out an exact estimate of the cost of all materials, and of all outside jobs. It, will horrify you, but the actual construction will eventually cost at least double what you estimated ! In military parlance, ” time spent in making a reconnaissance is never wasted.” It is impossible to overdo the elementary mathematics and drawing. side of the job. I personally knOw of various promising cars which were never completed because the cost got out of hand. Don’t spend so nmeh on building a car that you can’t afford to race it ! Remember that entry fees are not the only expense. You will have to face hotel bills at all but local events, and may tind, as I do, that the most attractive events are always held a long way from where you live. Then there are meehanies, and they are a problem. Even if you take ” amateur ” mechanics, you usually find that they expect you to pay at least -their hotel bills. (Friends acting as mechanics can be very difficult, and may go after beer Or blondes when they sliotikl be working On the motor.) Never take any notice of anybody else’s cost of building a car, because everyone’s facilities vary. I have known cheap parts to come out of the back doors of’ factories. Write lots of letters to makers of equipuiciit and parts. Some are immensely helpful, and the others can only say ” No “
Choice of engine. If you are in a position to make your own engine, you are rather beyond my class. Do try to use the simplest motor you can. A certain sill:el-charged o.h.c. engine costs nearly £200 for re-rollering its big-ends, because of fantastic unbuilding of the built-up crank. Other jobs on that engine are p.,0 rata. Make sure, therefore, that you are not biting off more than you can chew in that direction. Do not get led away by the snob-appeal of an engine’s name. That reminds me of a friend who was hypnotised into buying a foreign car by a lot of blah about
“racing pedigree” and “thoroughbred,” and all that. It was a very bad car, so he took it to the c,oncessionnaire’s service station, where an enormously exalted foreign mechanic, waited on hand and foot by lesser acolytes, consented to look inside the bonnet of the car. My friend, immensely impressed by this semireligious ritual, felt that he must say something to show what a discerning motorist he was. “1 say,” he enquired, “why does it have sixteen sparking plugs and only one carburetter? ” The high priest gave him one horrified look, as if a sacrilege had been committed in the temple, and said : “Monsieur le Patron say ‘von carburateur,’ so von earburateur you ‘ave !”
However, to return to sanity. There are some very promising engines in the most unexpected places. Don’t forget the smaller aero engines. Some of these are of awkward shapes for installation in a car, but there are some, particularly the American 4and 6-cylinder horizontally opposed units, which are of convenient shape and size, and have a splendid power-to-weight ratio. Remember, though, that their limited range of revolutions may mean a heavy and elaborate gearbox, and acceleration may suffer accordingly.
My own experience has included the coupling together of various numbers of engines. This has been immensely interesting work, and it is certainly a cheap and light method of building a power plant of the required size. There are quite a lot of snags to be overcome, but the method I evolved was reliable and not unsuccessful.
Among the troubles which I experienced in the early stages was the failure of the engines to maintain their correct timing relative to each other, due to sheared keys, shock-absorber sprockets riding over their cams, and similar small mechanical failures. The first intimation I used to get that this had happened was that, on engaging an indirect gear, the gearbox casing would split right across, owing to the increased momentary torque of two cylinders firing simultaneously. The speed on top gear did not seem greatly affected. However, having overcome such difficulties as these, I eventually coupled four V-twin engines satisfactorily.
It would be all too easy to talk • for hours on that subject, but I fear that it is of somewhat limited appeal, and as there are a lot of other aspects I want to discuss, I shall say no more about coupled engines.
Anyway, whatever type of power plant you fancy, ferret out real, and not fictitious, b.h.p. Chassis. Try to make it so that the weight distribution can be altered if you have made a mistake. Some very brilliant people insist that chassis and body should be a monocoque, stressed skin construction. I don’t agree. I think that the actual frame should be as simple as possible, because it is a melancholy fact, which must be faced, that one’s motor-car is sometimes going to run out of road, and if it be so constructed that it can be ” bent straight again” quickly, it will not entail missing some of the best events of the season. Of course, everybody knows that a good driver doesn’t have accidents, but it’s only too
easy to go into a corner with ” Bira ” and come out of it with a couple of buckled wheels. I am, in any case, not convinced that the body-cum-chassis is all that lighter for a racing single-seater.
You cannot mention chassis design without discussing roadholding. After giving a lot of thought to roadholding, I have come to the conclusion that no such thing exists among fast, light racing cars. However, the more nearly under control you are, the faster you will be able to negotiate the hazards of the racecourse, so it is worth doing an immense amount of work on “chassis tuning.” The very closest attention to every little detail of the chassis frame, steering, and suspension, is infinitely worth while, and I have knocked more than two whole seconds off the time of a car up Shelsley by painstaking work of this nature.
When testing the car during roadholding research, it is very difficult to know whether you are really cornering fast, or whether it just ” feels fast.” The only way of telling is by direct comparison with other racing cars during practice, and you should ascertain from the drivers, if possible, whether they were “really trying” on the occasion when you motored in close company.
As regards points of design, the old “hard ” suspension is finished, and one can say good-bye at last to the semielliptic leaf spring and the friction shockabsorber. I regret that I have wasted a great deal of my life with the solid, differential-less rear axle, but this cannot cope with modern systems at all on sharp corners, as it promotes unproductive skidding. This is a great pity, because the solid axle is so attractive from the point of view of the amateur “manufacturer” with limited machining facilities.
I have always found that when I have first completed a car, it seems absolutely impossible to drive, and this causes the greatest despondency till one gradually gets it to behave itself, by careful attention to small details. This need not worry the “specialist,” because even E.R.A. and Auto-Union made a complete fiasco of their first races, due to roadholding bothers. Of course, roadholding has to be so much better for racing than for more normal use, that these difficulties are understandable.
Weight. Most people are bitterly disappointed at the great weight of their ” Specials ” when finished. Get yourself weight-conscious by spending an evening weighing every component you can think of. Personally, I was rather surprised at the great difference in weight of varying tyre and wheel equipment. On one 11-litre car, the change from the old highpressure to modern low-pressure tyres put the weight up a whole cwt., and unsprung weight at that. By the way, the complete electrical equipment of a road car is abominably heavy, and may form quite a large percentage of the weight of a small sports car. It is so easy to think that a car consists of an engine, gearbox, couple of axles, and precious little else. It’s what one might term “the etcs.” that make up the weight. Engines are most deceiving things in the matter of weight. Some engines which are ” all light alloy ” are sur
prisingly heavy, and one of the best production engines for power-to-weight ratio had no non-ferrous alloy except pistons. So you can’t go by appearances. Brakes. Brakes are a terrible stumbling block. They are never big enough, and always much too heavy. A great deal of weight can be saved by using linered light-alloy drums, but they are very expensive, and have given a lot of trouble. The very beautiful light-alloy drums of the racing Mercedes-Benz had to be thrown away after every race. As the weight of brakes is unsprung, it is suggested that an entire revision of the present method is due, such as liquidcooled brakes inside the car, driven by shafts from the wheels. This would fit in very well with a four-wheel drive layout. In order to take the record for a rather bumpy sprint course, I removed my back brakes to get lower unsprung weight on the driving wheels, and was successful in taking the record. When adapting proprietary brakes to a
Special,” never lighten the drums. They need to be as rigid as possible, and integral fins are best. Shrunk-on aluminium fins look very nice, but are usually rather a failure from the rigidity and heatdissipation point of view. I have found east-iron drums best. No lining that I have come across will give a really high coefficient of friction with hardened steel liners, and mild steel drums are hopeless. A lot of weight can be saved by judicious lightening of back plates, without spoiling their rigidity. Holes can be cut for cooling, but should be covered with gauze against ingress of dirt. The funnel affairs which are fitted to some cars to scoop up the air probably do no such thing, as the air flow round the wheels is certainly not as simple as that. Something may have to be done to stop water getting into the brakes. It is a good idea to make special arrangements for heat insulation and cooling of hydraulic brake cylinders to avoid boiling the fluid. It is very desirable to provide two leading shoe operation, but this can be of the simplest character for a racing car, as no provision need be made for reversing.
Any weight reduction in the car gives a great increase in braking power. Any very slight increase in maximum speed may make what you thought were a superlative set of brakes into totally inadequate ones ; “inertia increases as square of speed.” Brake and brake-lining firms have an immense amount of experimental data, and braking is becoming an exact science. So also is the use of them by racing drivers, and . the Italians called Taruffi ” ii frevatore.”
Modern suspension systems, which aim to keep all wheels on the road all the time, render even heavier braking possible, and this, of course, places an even heavier load on the brakes. The very slightest tendency for the front wheels to bounce will enormously increase braking distances, and if you have a light car without i.f.s., much experimenting with tyre pressures and shockers is worth while. I am most careful of this, and balancing. Rear brakes are not so powerful, but can cause instability. Transmission. This is often unnecessarily heavy. If you have a light car, the greatest stress you can apply is to spin the wheels at the getaway, so there is no
need to use sueb:.a hefty gearbox, etc., as if the same engine were propelling a limousine. It is important to keep flatly wheel as light as possible, and there is no need for a flywheel, as such, on a mull icylindered job. There are numerous reasons for this, particularly less shock to transmission on a snap change, and the engine will slow instantly if you take your foot off for wheelspin. Back wheels and tyres should be as light as possible for the same reason, and twin wheels and tyres can just add that little extra inertia that will cause transmission failure. Do not have any more gears than you need. At least four are essential with small blown engines, but with engines giving good power at the bottom of the scale it is waste of time to keep shifting gears. My last ” Special ” was a 4-litre, 200-b.h.p., 111-cwt. job, and only had two gears. On some courses I didn’t change at all. Racing has rather grown up on a legacy of constant gear-changing, but it’s
vice, not a virtue, and if one were privileged to watch the famous Bergmeister, Hans Stuck, in his short-chassis Auto-Union, it was just like a Buick— only faster.
As for type of gearbox I love handling the Cotal electric, and Whatever you say about the Wilson box, it has the advantage of not needing a hand at an awkward moment. There is still a great deal to be said for a really good ” crash ” box, provided it’s robust enough to stand pulling through the up-changes with the throttle open. Propeller shafts should be short and well balanced, with universals ample to carry the urge. Fabric universals are quite useless for a racing car. Do not forget that a propeller shaft adrift may easily have fatal consequences, so do not economise over this item any more than you would over steering parts. The best is .good enough—just ! I have had a .great deal of experience with chain drive. This is very light, is reliable if properly carried out, and efficient, but requires fairly frequent replacement. Most people regard chain drive as being very pre-last-war, but I refuse to believe that it is finished, and shall continue to use it. Look at the very light unsprung weight of the old chain-drive racers. They had everything that the muchboosted De Dion system has, and each chain incorporates its own constant velocity universal joints I have never had to retire with chain trouble.
Bodywork. On my last car I had the whole bonnet, front cowling, and scuttle as One unit. This was very light and strong, and when removed left a virtually stripped chassis for quick and easy repairs. The tail was located on pegs, and required only two bolts to be undone for complete removal. Except on courses that permit very high speeds, I do not advocate a full-length undershield. It gets in the way of work, and in the event of things going wrong, can get filled with blazing petrol and oil which would otherwise fall harmlessly to the ground. I have seen a disastrous accident caused thereby. A streamlined body totally enclosing all wheels, lamps, etc., is a certainty for sports cars, bat not for racing cars except for very high-speed events. Reason : the front mudguards and headlamps, plus their brackets and supports, may reduce the speed of a fast sports car by as touch as .20 Sc-) you arry,1 incorporate t hew to the body streamlining. It ehc;Iper
h.in fitting a blower. On ‘acni ! car.,, however, low Nveight, lyre and brake cooling, and good visibility, are I be things that matter. Do concentrate on doing everything possilde to reduce frontal area. Redwing Wind resistance of a car also makes it. steadier at high speed, because you get less high-speed wheelspin in pushing the thing through the air. Also, rear tyres last longer.
Future trend uf design. One must incorporate the very latest ideas in a ” Special,” because they take a long time to make, and may be out of date when finished. Of course, if the post-war racing car is to have an i.e. or closedcircuit mercury-vapour turbine, with four-wheel electrical transmission and brakes, then ” we’ve had it.” However, that seems almost as unlikely as jet propulsion. Personally, I feel that classith-qttion Of ears by engine capacity has produced unfortunate results. There is no virtue whatever in a small engine giving great power per c.c. It’s the power-toWeight ratio that counts. For instance, equal speeds have been obtained by smallcapacity blown motors and considerably larger unblown ones. Difference ? Small machines did 5 m.p.g. of expensive ” dope,” and their immensely expensive little engines needed constant expert servicing. A big, cheap, simple engine could give the same performance on 20 m.p.g. of pump fuel, with great reliability. Yet most people would say that the small car was the better motor ! I hope that regulations can in future be drafted to avoid this worship of .overstressed small engines. It is obvious that the next development is four-wheel drive for racing. For obvious reasons nothing like the power can be transmitted through the front wheels in comparison with the rear—for a typical light racing car it would be of the order of 20 per cent. under average conditions. However, wheelspin, even at high speeds, is the limiting factor nowadays, so we will eventually have to make the front wheels do their share. So far it has not been applied without marring controllability of the car, but the first really controllable four-drive job, with brakes mounted inboard for reduced unsprung weight, will sweep all before it in sprints, hill climbs, and the more tortuous road circuits. (But not just a supercharged Jeep 1) This matter of transmitting the power to the road is not generally fully understood by people who have not had the good fortune to handle a really quick light motor. With my 4-litre car, one is virtually always embarrassed by wheelspin or incipient wheelspin, even accelerating
Quite apart from waste of power and loss of acceleration, this has a very bad effect on the stability of the car, and I have found it necessary to concentrate More weight at the back of the car than is desirable from other weight-distribution standpoints. One does not always know that wheelspin is taking place, till taking the foot off the accelerator before a corner, one obtains sudden acceleration momentarily instead of deceleration. This always frightens me. Details affecting driving. It is most important to tune the engine of a li”ht. fast car so that response h? liii. :wccici.:11(ir Is h11.:, I he same, alwa?s and sini>oth. A slight •• miss ” Nyhich suddenly riHits itself inay give a sufficient, sudden increase of power to spin you off
the road. Tile Alerc6ch’!s-lienz racing drivers found the big 5!,-litre Straight eights troublesome in this respect, if they were not in absolutely impeccable tune, and the greater fluency of the 12-cylinder engines was one reason illy the later 3-litres compared so well with the larger faster machines in their lap times.
Steering gear ratio. This depends on 13 rime; factors, especially the weight distribution. If this is such that the car goes into, and comes out of, its skids slowly, quite low-geared Steering is adequate, but if you have a car that skids suddenly you need high-geared steering to keep up with it. There is no feeling so hopeless as trying to keep the rear wheels behind when they want to come in front if your steering is too low-geared. I have a preference for rack and pinion steering which I used in my last car, but in any case I like a fabric universal joint in the steering column in case racing stresses put things Out of line. A springspoked wheel is a splendid thing for avoiding injuries in a crash. I can assure you that a broken rigid spoke in the tummy is no joke at all. Caster angle is usually very critical with a conventional front axle, and different values should be tried, but ” independent ” seems ‘fairly indifferent to this. Violent vibration is very tiring indeed for the driver in all but the shortest events. It may seem incredible, but when I had trouble with a bad vibration period during engine coupling experiments, I found that the violent shaking of one’s head affected the eyesight, everything appearing as through a mist. Another dinieulty with eyesight was the splashes of alcohol fuel which were blown back through the bonnet louvres. During tuning and racing, one seems to absorb a good deal of alcohol fuel into the body, and one must be careful if one resorts to stimulants afterwards, or drunkenness will quickly result. A certain engine, with exposed drive to the overhead camshafts, used to live in an atmosphere highly charged with castor base oil, which was absorbed by the driver with embarrassing effect.
General summary. I do not, of course, know .what form racing will take after the war, or what cars one will have to compete against. A large number of the cars which were racing before the war were Continental machines, built for Grand Prix racing some years previously. Although potentially formidable, most Of these ears failed to live up to their famous names because, without the works behind them, they just weren’t properly prepared. In that, of course, they underline my previous remarks advocating a simple type of engine, perfectly tuned. However, some of these cars were in the habit of jettisoning certain of their most vital parts when travelling at speed; but the British public loves a foreign car, and apparently doesn’t mind being mown down by runaway wheels off same. A famous foreign designer can produce racing cars in which, if a tiny chain loses a pin, the machine becomes brakeless. Continued on page 76
••••••••••••••••••••••••••••••••••••• HOW TO BUILD YOUR OWN CAR —continued from page 69
This, gentlemen, is the eccentricity of genius, but don’t for a moment imagine that you or I will be allowed to get away with anything like that.
Race organisers view all ” Specials ” with suspicion, and, quite apart from all questions of personal safety, you must construct your car so that it has an enormous factor of safety in all steering, suspension, and brake parts. All parts connected with the steering and suspension of your car should be polished, and never painted. I used to throw away my steering arms after every few races, and fit new ones. Even after the slightest crash, one should be absolutely honest with oneself in replacing any part that might have suffered damage.
I think that in building a ” Special ” one should strive to obtain a pleasing appearance. Usually, one is running short of cash by the time the body is built, and, anyway, one is in a burry to go racing with the new toy. However, a ” Special ” represents the expenditure of an immense amount of time and bard work, not to mention filthy lucre, and after it has won you some prizes, it will be one of your most treasured possessions, the joy of owning which will be all the keener if it looks the part. I must admit., though, that the greatest joy I got front contemplating my first ” Special ” was in counting the myriads of holes in the thing, and realising I hat I had drilled every single one of them with a breast drill of the variety which engincetS call ” gut-buster.”
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