THE AUSTIN SEVEN “BROOKLANDS ” SUPER-SPORTS MODEL.
Further Details Concerning the Interesting “Speed-Mite.”
THE commencement of a new racing season provides a fitting opportunity of drawing the attention of our readers to the Austin Seven ” Brooklands SuperSports Model, which since we reviewed it last year has undergone various improvements, resulting from the many successful events in which it has participated.
As our readers are aware, this model is specifically intended for racing purposes, and though it can be used for fast touring work, the makers do not recommend it for ordinary road work; and, in fact, now list a special model for road competitions, which is known as the Austin Cup Model, and which we hope to review in connection with the forthcoming London-Land’s End Trial.
light pistons, a high lift camshaft and modified timing gears. To enable the engine to maintain very high speeds, special K.E. valves are fitted, and these are provided with double valve springs and special tappets.
In place of the two Zenith Carburettors used on the former models, the makers have adopted a single Solex, size 30 mm., and the induction pipe has been improved to create greater turbulence of the mixture.
Perhaps the most important modification of the engine is an improved lubrication system, for with the standard arrangement there was a certain amount of difficulty in ensuring the oil supply to No. 3 big-end when high speeds were kept up for long periods.
With regard to the main features of the chassis, very few modifications have been found necessary, and the general methods of hotting the engine, carried out by Messrs. Gordon England, Ltd., remain much the same as heretofore.
Specification Details.—For the benefit of new readers, we give a few details of the specification, together with the more recent modifications.
The engine has a capacity of 747.5 cubic centimetres, the cylinders measuring 56 mm. bore by 76 mm. stroke, so that the car can be entered in any sporting events of the 750 category. In addition to a careful polishing of the parts, a special high compression cylinder head is fitted, extra Even though the pressure of the oil supply was increased, this did not altogether cure the difficulty, but in a way created fresh problems in keeping the plugs clean. For a long time a solution appeared difficult, until it was discovered that the centrifugal force of the crankshaft at high speeds was so great as to overcome the pressure of the oil in certain of the crankshaft ducts, which led to the introduction of special pipes arranged circumferentially on the crankwebs, so that the centrifugal force assists the flow of oil to all the bearings. This feature has resulted in a reduction of no less than 10 lbs. per square inch in the pressure of the oil supply, thus reducing the oil consumption and keeping the
While following the same principles as before, the bodywork also has undergone various small improvements, and is of patent construction, framed in threeply and white wood. All the panelling is of aluminium, which is now finished with varnish. Beneath the body is a detachable streamline undershield, and streamline faring is also fitted over the front axle. It has been proved by actual tests that the wind-resistance reducing properties of the body actually give a substantial increase of speed, and that the mere fitting of wings, hood and a small windscreen reduce the speed of the car by as much as ten miles per hour.
A special crown wheel and pinion are fitted to the rear axle, which gives the following gear ratios :—First gear, 14.5 to ; second gear, 8.17 to 1, and top gear, 4.4 to I.
float. For racing, a 24 choke and 130 main jet may be used.
Adjustment for the tappets is obtained by varying the thickness of the pad fitting into the top of each tappet. To increase the clearance, these pads should be rubbed down on a sheet of emery cloth placed on a flat surface, an operation that may be required occasionally after valve grinding operations. The normal clearance for the exhaust valves should be .oio in., and for the inlet valves, .006 in.
Notes on Performance..
The performance of the Austin Seven” Brooklands ” Super-Sports Model is so well known that there is really no need to occupy space in further comments in this direction. Its long list of successes speaks
Every car is sold with a Brooklands certificate that it has accomplished 75 miles per hour before delivery. Thirty miles per hour is obtainable on bottom gear and fifty-five miles per hour on second gear.
The engine develops full power at its maximum number of revolutions, which is approximately 5,000 per minute, and for the best results Aviation petrol is recommended and Castrol “R” for lubrication.
The engine is naturally very sensitive to the ignition, and the best results are obtained by setting the contact points of the magneto to break at 21 in. before top dead centre, measured on the flywheel rim, with the contact breaker in the fully advanced position. This setting gives the best normal results, though slight variations may be found to be beneficial for special purposes on individual engines. The standard setting for the Solex carburettor is a 22 choke, 110 main jet and 50 pilot jet, using a 47 gramme
volumes, and is far greater praise of the general excellence of this wonderful little machine than anything we can say about it.
We submitted one of the newest examples to a series of tests extending over a week-end recently, and find nothing but appreciation with regard to every detail.
For this reason we hesitate to offer any further comments, for nothing is so boring to read as a reiteration of “excellent, excellent, excellent,” even though in this particular instance it happens to be merited.
Hitherto we have been able to find some points for comments of a critical nature in every make of car handled during our tests, but must frankly admit the ” Brooklands ” Austin stumped us altogether, which, after all, is perhaps the best testimony that we can offer.