Impressive improvement in acceleration from M.A.G.-blown engine
Philip Mann, whose very lovely 3-litre Bentley is well known to vintage-car enthusiasts, has as a staff car for his company, Mann & Son (London) Ltd., a 1958 Volkswagen saloon. Now amongst the Volkswagen’s shortcomings is a sad lack of any real performance. Mr. Mann decided to make this good by having an M.A.G. supercharger fitted to the car. This little Roots-type supercharger or blower is made by the Swiss engineering firm known in this country because they supplied the i.o.e. vee-twin engines used many years ago in the Morgan three-wheeler and by several of our motor-cycle manufacturers.
The supercharger is mounted on a bracket on the near-side of the VW engine, this bracket being attached to the inlet manifolding and hot-spot pipe on that side. The drive is by an additional belt pulley and belt mounted outside the existing cooling-fan-cum-dynamo pulley, the supercharger running at approximately one-and-a-half times engine speed. The intake pipe mates up with the normal carburetter flange and this pipe incorporates a bracket which carries the normal drum-type air-cleaner, which is connected by flexible tubing to the carburetter above the blower. The Solex carburetter is larger than that used on the normal VW engine and the M.A.G. supercharger gives a boost of about 3 lb./sq. in. The supercharger gears are lubricated from a container on the off-side of the engine which has a thumb-operated plunger whereby oil can be fed by tube to the supercharger, a glass sight-level providing a check that lubricant is getting through. This plunger is operated “once in a while,” and as the owner of a blown VW is likely to lift the bonnet pretty frequently to display the new-found power to admiring friends, it isn’t likely to be overlooked.
The M.A.G.installation is extremely neat, fitting into the available space without any alteration having to be made to the exterior of the car, so that outwardly the blown VW is indistinguishable from any other. It is when the throttle is opened that it gives itself away!
The acceleration is improved to an impressive degree, as is evident almost as soon as the car is driven — just how much improvement is gained is shown convincingly by the figures in the accompanying table. Before ever a stop-watch is used, however, the vivid pick-up, particularly in third gear, is appreciated and the driver finds this VW quickly attaining a genuine 60 m.p.h. so that a very easy cruising speed of 68-70 m.p.h is maintained far more frequently than with the standard model which, after traffic checks, crawls sluggishly back to such speeds. Here let it be said that we have discovered that every VW seems to have a speedometer optimistic by approximately 5 m.p.h. throughout its range — those who have not checked theirs should read 65 and 73-76 m.p.h. for the speeds referred to above!
Mr. Mann told us that at first some difficulty was experienced with the accelerator linkage, the throttle being either shut or fully open. However, Don McKenzie, the Bentley tuning expert, was consulted and now the action is only slightly removed from normal. A rather fast tick-over is advisable as the engine tends to “hunt” somewhat. Another early discovery was that the normal Bosch plugs couldn’t stand up to the boost, but although experiments are continuing, over the 255 miles that we covered in this intriguing Volkswagen, no plug or starting trouble was experienced, nor does the blown engine “run-on.” Incidentally, supercharging increases considerably the efficiency of the heater; with the windows open the effect is like turning on a hair-dryer.
The very evident and useable increase in performance is accompanied by delightful sizzing noises from behind, which emphasise the impression that here is the “poor man’s Porsche.” Mr. Mann’s car is standard, the blower installation apart, except for an anti-roll bar and a Motometer combining ammeter, oil thermometer and fuel gauge within one small dial. We did not check petrol consumption but are told that 32 m.p.g. (of 100-octane fuel) is obtained on long runs but that in traffic, unless the enjoyment of beating bigger cars and unsuspecting fellow VW drivers from the lights is considerably curtailed, this rises to unmentionable figures. Oil consumption is not affected by supercharging, i.e., no replenishment is necessary between sump draining every 1,500 miles,
After motoring some very swift miles and driving from London to Hampshire almost as quickly as we have done in any car, we took some performance figures which illustrate better than mere words the worth of the M.A.G. supercharger installation. By way of comparison we also timed another VW, a normal 1957 car in good condition, which had run 21,000 miles. The same driver drove both cars. It soon became evident that true speeds of 16 m.p.h., 45 m.p.h. and 69 m.p.h. were the blown car’s maxima in first, second and third gears (speedometer readings of 20, 50 and 75 m.p.h., respectively), although acceleration benefited by changing up somewhat earlier in second gear. Severe clutch slip was experienced when accelerating hard in second gear and careful throttle opening was necessary in that gear. As to maximum speed, the speedometer needle went “off the dial” of the 80-m.p.h speedometer very readily, the genuine maximum being near to or above a genuine 80 m.p.h. The true maxima in the gears of the normal car were, respectively, 16, 36 and 47 m.p.h.
Over a s.s.1/4-mile the supercharged car gained two seconds, doing an indicated 66 m.p.h. at the end, compared to an indicated 58 m.p.h. of the normal VW. More impressive were the 0-50 and 0-60 m.p.h. times, as the table shows, and it is particularly creditable that the blown car reduces the 50-60 m.p.h. time by 7.8 see. (the higher third gear speed being extremely helpful) and gets to 60 m.p.h. from a standstill 12.1 sec. sooner than is possible with a normal VW. The cost of the conversion is in the region of £100.
We are indebted to Mr. Mann for letting us experience the exhilaration which results from adding a mild puff to the Volkswagen’s restricted induction arrangements. — W. B.
Acceleration Table (Speedometer corrected for optimism): 1 = Normal 1957 VW; 2 = M.A.G. supercharged 1958 VW
0 – 50 m.p.h.: 1 — 20.0 sec. 2 — 15.7 sec.
0 – 60 m.p.h.: 1 — 33.1 sec. 2 — 21.0 sec.
50 – 60 m.p.h.: 1 — 13.1 sec 2 — 5.3 sec.
s.s 1/4 mile: 1 — 23.7 sec. 2 — 21.7 sec.
0 – 60 – 0 m.p.h. — 2 — 24.3 sec.