SILENCER TESTS.

Press, Volume LX, Issue 18230, 14 November 1924, Page 18

SILENCER TESTS.

NO LOSS OF : ENGINE EFFICIENCY.

Recently we .suggested the valuable aid a competitive test of engine ■ silencers ' might •; give .in meeting several troubles which are afflicting sections of the motoring movement because of the public's complaints against ncisy exhausts (says the "Field"). .. By' a curious coincidence, Cagt. ;W. G. Aston, with the assistance of the Taloot Company, was even then moving in the same direction by carrying out what we take to- be a test of .a Talbot light ear engine fitted "with a standard Talbot silencer, evidently intent' on the same issue. In the "Autocar" he sets cut in the form of a .graph the result of a bench test of this engine when, fitted with the exhaust silencer, and with the silencer removed and the exhaust open, into a plain pipe. •. The, test ranged from 500 to 3000 r.p.m., and the power development rose from 3 to just over 18 h.p. , For everyjpraotical purpose the power curve was identical throughout the entire range of engine speeds, whether the silencer was in operation or not. Indeed, silencer line is the better one, for although it shows a slightly lower power up to .1250 r.p.m.,' it actually discloses jnore power than the open exhaust beyond 2500 r.p.m. That, we recall, reproduces the result which was credited to the -Rover motor-bicycle in a silencer competitive test carried out by the Auto-Cycle Union some years pricr to th 4 war, and goes to show that there is no need entirely to dispense with exhaust boxes, even for racing purposes,, because then the engine fs running at' its maximum speed and the silencer probably is actually an aid to power as, well as to silence. Of ccurse, it does not- settle the problem we all want to eeo investigated—how to .silence a'n engine without diminishing its power output, because the Talbot silencer, while efficient as such devices go, does not fulfill everybody's idea of engine silence, an-J Captain Aston's test, it will be nofcrl, was carried out with a pipe lead to the exhaust, which, to an extent, possibly throttled it.' It would have'been more informative had he stripped the exhaust manifold and permitted the engine to discharge into the air. Th.it reflection, is not to say that we are dis-. satisfied with his process—quite the reverse, fcT lie has shown those who race small-engined. cars , and motor-cycles that they do not necessarily gain in power by removing ' their silencers, which almost eiveryone does when permitted in a 6pee'd or hill-climb competition. Of course, a 1 clogged or dirty exhaust box will choke an engine, and probably if a greater facility for cleaning it were provided there would, be less, desire to dispense with it. As a rule, there ig small complaint to lie. made against motor-car exhausts, although eooio' of the faster-turning

small-car engines are quite eastly_hear3 lone before they are seen. It is tne motcT-cvcle which is the greatest smner and its noise often accounts fo the'police warning or prosecuting its rider for overspeedyig. If f car motor-cycle is travelling fast, the ee°se of speed is exaggerated by a noisy exhaust. The same, may be said cf any form of noise involved, and here let us admit that quite a wnsideraWe number of otherwise desirable smsm cars ar noisy on.tTieTr lower,; • gears —a penalty accruing 'from high cramc shaft 'speeds. '