DIRT TRACK RACING IN AMERICA

DIRT TRACK RACING IN AMERICA

Writing about American racing-cars for a British public is at best a considerable assignment, for in order to make the subject at all intelligible to all the readers, it becomes highly necessary to cover much ground already well known to many. However, as I have seldom seen in English motoring papers articles which would give a. picture of what American racing practice really is, I shall prepare to dodge brickbats and knock-on hammers, and begin at the beginning. Practically all present-day racing in America is done on half-mile dirt ovals. 1:he very best of these are usually none too good, while surfaces on the worst of them might be compared with some of your trials courses. Racing on these tracks has been going on for long enough so that a definite type of car and method of driving have been evolved to produce

best results. At any rate, any radical departure from them has not, up to now, met with much success. Cornering, roughly speaking, consists in braking good and hard for a fraction Of a second when beginning to enter the turn, steering into the inside rail just long .enough to get the car pointed at the infield, then putting the wheel hard over the other way, stamping on the throttle, and going around the turn in one long skid. While in the turn, the car is headed towards the infield, and moving in a direction perhaps forty-five degrees to its

4-1 \ n centre-line. Position is controlled more or less by the throttle ; should the car get too near the outside rail, more throttle (if you haven't used it all up l) will usually move it in, while should it get too near the inside rail, less throttle will certainly let it drift out. It is really a case of centrifugal force versus wheelspin, and is not as easy as it sounds. It will be readily understood that a primary requirement for these conditions is much and instant horsepower. This has been met by the use of four-cylinder engines of between 31 and 4l-litre capacity. Incidentally, although there is no such thing as handicap racing, and C-litre engines are allowed by the rules, few drivers have found it profitable to go that high, probably because of the small size of the tracks. Chassis requirements are, obviously, short wheelbase, with the average being about ninety-five inches, and great stiffness. The chassis problem is further complicated by the not surpr:sing fact that competition tyres, or " rough " rubber," at the end of all this torque can dig great big holes in the turns in no time

at all. Alter several races the surface is usually such that the cars actually leap from hole to hale, which is why some people call them " goats." Since, despite all this, the fast cars lap in between twentysix and thirty seconds on a half-mile track, it will be easily understood that the modern dirt-track car is nothing if not durable.

I hope it will be distinctly understood that these cars have been developed solely for this type of racing, and can no more be compared with road-racing cars than polo ponies can be compared with racehorses.

It may be a surprise to some to learn that while there are, in this country, certain recognised builders of racing-cars, their shops can in no way be compared to the factories whence spring cars like Bugattis, Alfas, Nashes, or Astons. Production is on order only, and limited in each case to a very few cars a year. The result is that most of the boys build their own. On the other hand the usual standard of workmanship is such that it is hard to distinguish whether a car has been built by a car builder or by a mechanic in his own shop.

The motor situation may be summed up briefly at this time by -saying that two types of Motors are most widely used, Millers and Ford conversions. The Miller designation has come these days to mean Miller type. Harry Miller himself has built very tew motors. in the past few years, but Fred Offenhauser, who was formerly associated with him, has continued to produce motors which, with a few changes, are the same as the old Millers. The oldest Millers now in top-line competition are the erstwhile 151 cu. in. (2.5-litre) Marine Fours. They all have bigger blocks now, giving a displacement of about 222 cu. in. (3.6 litre). Very similar are the later motors which were built as 220s, except that, designed for the increased displacement, they are generally more satisfactory. The latest motors are the 255 cu. in. Pours, (4.25-litre), which are slightly enlarged editions of the 220s. Most of the latter have been built by Ofienhauser. All three types have two overhead cams, driven by a gear tower at the front of the

motor. he majority are eight-valve motors. Nearly all the Ford conversions are built round the Model A or B four cylinder block, As yet, the V8 motor has received little attention on the dirt tracks, though some of them have run at Indianapolis. The modifications, for the four-cylinder Motor, consist of a new head of one of four types, depending on valve action : side valve (called flat heads), rocker arm 0.11. valves, single o.h. cam and double o.h. cam. The flat heads are mostly Winfield ; rocker arm heads may be Riley, Cragar, or MacDowel!; single o.h. cam heads, usually chain driven, include Hal, Rutherford, and MacDowell ; and double o.h. cam heads include Cragar, MacDowell, Vance, Green, and Hal. There are many others also available, so it will be seen that the choice of head, given a Ford block, is

very wide. In addition to the change in head, carburetters, manifolds, camshafts, lubricating systems, and ignition are usually changed as well, so that quite often the only Ford parts left are the block, shaft, and connecting rods.

Suspension started with the usual four semi-elliptic springs. Presently the trend changed to semi-clliptics in front and a transverse spring in the rear, which, nearly everyone agreed, made the cars handle better. First thing, of course, would be to get a suitable frame. Most of the newer ones are of the " round-nose " type, made in the form of a very deep letter P. The rounded part forms the front, and clips directly to the centre of the transverse spring. The sides are perfectly straight in plan, except in a few cases where the last foot or so is bent in to follow the contour of the tail. In profile, the frame runs along straight to within about a foot of the rear axle, where a conventional kick-up begins, which carries it over that member. Immediately over the rear axle, a cross member is fitted, which fits over the topmost portion of the rear transverse spring. The side rails continue past this for a foot or so, and carry the

tail only The frame may be obtained in one of three ways. It may be obtained from 4 builder, such as Dreyer, who makes them in comparative quantity. Axles Come next. Here preference seems about divided between Chrysler front axles, vintage of about 1930, and Ford axles. The Chryslers, you may remember, are tubular, and quite generally resemble the Miller axles except that they are slightly curved. With the transverse spring, Ford spring perches are most convenient to use, and the Chrysler Continued on page 68