INFLATED PERFORMANCE

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45

INIFILATIM IDIEUECIUMANCIE MARSHALL SUPERCHARGING FOR POPULAR CARS

Having a great respect for the Morris Eight, we were interested when Marshall Drew and Company, Ltd., invited us to try a saloon edition to which a Marshall supercharger installation had been applied. No alterations of any sort had been made beyond the a d dition of the blower set, the cost of which is 09 10s. (fitting 30/extra) in this particular instance. The Roots-type Marshall supercharger is rigidly mounted over the cylinder-bead, is lubricated automatically from a tapping of the engine circulation system, and feeds into a special ribbed intake pipe. An S.U. carburetter is fitted, of larger size than that supplied as standard on the Morris Eight. In making the test we asked an experienced driver to follow us in an unblown Morris Eight saloon of identical type, and over give and-take roads our superior acceleration and higher cruising speed were very evident. The Marshall-blown car settles down so easily to a erasing speed of 50-5.5 m.p.h., and attains this pace so rapidly after checks, than an ordinary car of the same type is soon left far behind. The engine of the car tested made a good deal of noise, especially when accelerating, but the blower is virtually unobtrusive. Its presence has greatly improved the low-speed running, so that top gear suffices down to a crawl and the subsequent pick-up is clean and regular. There was considerable lost motion in the throttle connections, to which one soon became

accustomed, and the engine stalled when the car was stationary unless the throttle Was depressed slightly. On one occasion considerable smoking accompanied by -a smell of burning was evident, but generally the temperature and oil-pressure remained normal. On a long hill with several acute bends and a gradient of 1 in 4 we climbed in second gear, four up, whereas the other Morris needed bottom gear and was reduced to a crawl with only the driver aboard. By using bottom gear momentarily on this hill a very fine ascent was made. On main-road hills this improvement in performance is naturally very pronounced, and materially improves the average speed capabilities. The actual acceleration figure from to 50 m.p.h. is 17.5 secs., which corresponds to a figure of 46 sees. for the same test with the latest type standard model. The car tested had been used extensively for experimentation and demonstration, and its steering and braking qualities did not encourage speed tests, but it -s understood that on second gear 45 m.p.h. is possible before valve-bounce intervenes, and that 72 m.p.h. is possible on top. These speeds represent an improvement of m.p.h. and 16 m.p.h. respectively over those obtainable from an unblown Morris Eight. The fuel consumption works out at 25 m.p.g., driven hard, but it is possible to use a different needle in the S.U. carburetter, when the performance is slightly reAuced and the consumption improved.

The engine started easily and did MA spit back or misfire, but it pinked excessively at certain throttle openings, in spite of the use of Cleveland Discol fuel. It has run 10,000 miles with the blower installed, since when, we are assured, no trouble of any sort has been experienced, and it would seem that the need for decarbonisation accounted for the pinking, particularly as the supercharge pressure is as high as 8 to 9 lb. per square inch, while the compression-ratio is standard. Naturally, special heads, stronger valve springs and raised-axle ratios can be utilised with supercharging if desired, but experience of this Morris Eight indicates that they are not essential to a substantial improvement in performance.