SPORTING CARS ON ROAD AND TRACK. THE 12/40 SUPERCHARGED MERCEDES.
ENGINE: Fourcylinder monobloc. O.H.V. 68 mm. by io8 mm. Fitted with Mercedes Patent Supercharger.
CLUTCH: Single Cone, leather faced.
GEAR BOX: Four speeds and reverse.
SUSPENSION: Semi-elliptic front ; full cantilever rear. REAR AXLE: Final drive by double bevel and pinion.
WHEELS: Detachable wire for 765 mm. by xo5 mm. tyres• Two spare wheels.
WEIGHT OF CHASSIS: 13 cwt.
PRICE: Two-seater 4775.
CONCESSIONAIRES: British Mercedes Ltd., 27-130, Long Acre, W.C.2. READERS who perused the recent article on “Super
charging in Theory and Practice “may be specially interested in the following review of the 12/40 h.p. Mercedes Semi-sports two-seater, as for some time past all the models of this famous make have been fitted with the Mercedes patent Supercharger, which has been developed with the object of rendering the apparatus suitable for everyday use. Before giving details of the series of tests to which the car was submitted, we will depart from our usual practice by describing the principal features of the chassis, as from its first introduction in the early days of motoring, the Mercedes has been the most extensively copied of all cars.
Engine and Chassis Details,
The engine, which is rated for taxation purposes as 11.5 h.p., is of the four-cylinder monobloc type, with a bore and stroke of 68 mm. and 1°8 mm. respectively, these dimensions giving a cubic capacity of 1,568 c.c., which of course place it just outside the light car category. The inclined overhead valves are operated by a single camshaft, which is driven by an enclosed vertical shaft at the rear of the engine, the whole of the valve mechanism being neatly enclosed and well lubricated. Extreme neatness of design characterises the entire lay-out of the power wait, and though to the uninitiated the engine may appear to be more complicated than those of the
usual type, a close inspection of the many refinements included shows that the whole design has been worked out with due consideration to the important matter of accessibility.
The clutch is of the single cone type with a leather face, and the gear ratios are as follows :—First speed zo to I; second speed 10 to ; third speed 6 to x; and top speed 4 to r. Thus it will be seen with the engine turning over at a fair number of revolutions per minute good maximum speeds are possible without any difficulty. With regard to the final drive, the arrangement calls for special comment by reason of the unique arrangement of two driving pinions and two bevels, which it is claimed obviates practically all wheel spin, when taking up the drive on difficult ground.
Arrangement of the Supercharger.
The most interesting feature of the Mercedes chassis is the arrangement of the supercharging apparatus, of which the blower, a comparatively small unit, is located at the front of the engine and is connected with the forward end of the crankshaft by means of a multiple disc clutch. The plates of the latter are caused to engage as the accelerator pedal is fully depressed, thus bringing the supercharger into action as the maximum engine revolutions are reached. In the Mercedes arrangement the carburettor is located between the engine and the blower, which obviates the usual difficulty of lubricating the internal parts of the latter, as in cases where the blower has to work in a petrol mist. Though the engine works admirably with the supercharger, as will be described later, the apparatus is somewhat on the small size compared with those used for racing purposes. This, as a matter of fact, is a very wise precaution, for it is admittedly risky to carry the supercharging effect to too high a point, especially in the case of cars intended for use by the general public, and when absolute reliaability is more essential than for racing cars habitually handled by experts and where mechanical attentions are not regarded as a serious drawback.
The Use of the Supercharger in Traffic.
Before taking the car on our test, we did a sort of preliminary canter in company with an expert from Mercedes House, who explained the various little points connected with the use of the supercharger, and thus instructed, we set off to make our own observations about the car, which are recorded as follows.
We found that while the gears could be engaged with comparative ease at almost any speed, the best changes were effected by pausing for a fraction of a second on the “double clutch,” and in all cases the act of changing is very similar to that which characterised the Mercedes of many years ago. In fact, there is something—a certain indefinable similarity—about the car that is strongly reminiscent of the old 60 li.p. “Mere.” chassis. Contrary to what might be imagined, it is possible and even convenient to use the supercharger for town
driving, though it is not suggested that novices should try the experiment before becoming accustomed to the astounding acceleration, which follows the full depression of the accelerator pedal.
Directly the first gear is engaged and the car is moving, the second gear should be introduced, and then if the road is clear, one may indulge in the new experience of allowing the engine to supercharge. On pushing the accelerator pedal right home, the clutch of the blower comes into action with a peculiar little whine, and in the same second the car leaps forward with a highpitched but not unmusical scream.
When about to change into third speed, the release of the accelerator in throwing the supercharger out of action causes the engine to give forth a prolonged ” 0-o-o-o-oh ! ” which almost becomes an appeal to the driver for a further spell of the supercharging exhilaration.
Top gear work on the 12 140 Mercedes is delightfully smooth, even at London traffic speeds. The short wheel base and the good driving position, coupled with the wonderful acceleration (one may be permitted to use the word ” wonderful ” in this case) make the car so easy to handle in traffic that one can take liberties with the London taxi-driver and generally beat him at his own game of dodging ‘buses and newspaper vans.
A Test on Brooklands.
If one is out to try any car w ith the turn of speed possessed by the Mercedes, Brook] ands is the only place near London where the test can be carried out without falling foul of police vigilance, so to Brooklands we went. As a matter of fact our pride suffered a distinct reverse, when trying the Supercharged Mercedes on the track for the first time, as attempts to get the speedometer
needle over to the 80 m.p.h. mark proved unavailing. But the spell on the track showed us the knack of using the supercharger, which was used to better effect somewhere else later on, when the needle went hard over for more than half a mile.
To get the best results from the engine, one must get up to a fairly high speed on third gear, then change into top and allow the car to pick up speed still further before the supercharger is brought into engagement. In these conditions the benefits are apparent at once, but otherwise the engine is handicapped by having to operate the blower, which is not working fast enough to exert any useful pressure on the carburettor. We kept the car hard at work for an hour on the track, to discover if it would develop any signs of distress or overheating, but the longer it ran the more it seemed to enjoy itself, so we eventually turned south for Bournemouth, after the engine had been submitted to a critical
examination by the group of racing experts shown in the photograph
Touring Impressions of the Mercedes.
Except for the run up the Hog’s Back, the GuildfordWinchester Road does not offer many opportunities for running such a car as the Mercedes on full throttle, but on the other hand, there is a good chance of observing the general touring qualities of a machine on such a route, and it should be remembered that the 12/40 Mercedes is put on the market as a chassis for fast touring rather than for sports purposes pure and simple. At high road speeds the car runs rock steady, though personally we should prefer to have shock absorbers fitted to take off
some of the bounce which occurs on really bad examples of our excellent roads. The car will corner fast without any tail wag, even on greasy surfaces.
Our trial trip of some two hundred miles under touring conditions emphasised some of the minor details we should like to have altered for our own use. Our first comment cOncerns the brakes, which are excellent for all ordinary purposes, but as soon as one begins to get above 70 m.p.h., the car does take rather a long time to slow down. The addition of four-wheel brakes would enable One to indulge in higher touring averages than at present, with the same degree of comfort and safety as is now possible up to speeds say of 55 m.p.h.
On the standard two-seater body as turned out by the makers the leg room has been rather overdone, with the result that there is quite a stretch to reach the clutch pedal when fully depressed.
The instrument board is very complete, but the lay-out is capable of improvement, for example, the speedometer is located on the extreme left of the driver, who cannot gauge the speed without turning his head. It may be mentioned that many Mercedes owners appear to get over the craving for four-wheel brakes, even though they express the intention of having them fitted when buying their cars. Perhaps it is that they content themselves with 50 m.p.h. as a touring speed, and unlike ourselves are not obliged to drive all out to discover the merits and demerits of different cars for strictly business purposes.
Notwithstanding the few minor criticisms mentioned above, we were very much impressed by the general qualities of the Mercedes in its latest form, and the makers have managed to retain the excellent characteristics of the pre-war models, besides demonstrating the value of supercharging for touring cars in no uncertain manner.