STRAIGHT-THROUGH EXHAUST

Evening Post, Volume CXIII, Issue 7, 9 January 1932, Page 8

STRAIGHT-THROUGH EXHAUST

-Enthusiasts who drive-sporty roadsters that have 'cut-outs and straight through exhausts will no doubt be surprised to learn that the use of a "straight-through" exhaust system increases petiol consumption by as much as twenty-five per cent, in some cases. Of course, a straight-through exhaust does away with "back-pressure" m the silencer and exhaust pipe, and piobably gitfes 'slightly, more1 spe^d1 and; livelier, per^rmaflcefaill'iat the'*erpienfe of '"'lii- . 'ff-THBj'qiiesticiKKlies .in' valye:'|fiiSiSg.; ■When'vthe c>was ' desighedrthe.-e'n-' gine'ers took into account the back-pres-, sure in the,,silejicer of the exhaust ejrs-l'tem-''an.di'°c'o^i)Ußtipn^-chambef^at''''th'e'' completion bit the;exhaust stroke,'and they that ;when:.the/inlet 'valve opened' the inflo# ;of gas ductiori'pipe.:would-meet with^a-certaiij' amount of pressure' or "back-pressure,J> diie^to'i/the.^exhaust gases still in the combustion chamber." "■• vv- ■-•-■-; ■■•.,-.

Consequently they arranged the valve timing so that the inlet valye would have an advanced and longer opening period in order to counterbalance the "back-pressure" and so that the cylinder and combustion chamber could be completely filled with-vapour. - ■ . • On removal of the silencer and having a, straight-through exhaust, ..the -back*pressure-is -done away with,-and" so when when the inlet valve opens coming vapour -from tiie; induction'pipe to} b.v.ercome,-. with a result that an exeessiye "quantity^ of ."petrol Vapour enters I tße^cylinderr-Jthe.direct' cause of the in-. c'r^.ase(i;;;'cbhsuinption: '■":: vjTh'ia. /increased fuel consumption, may■/;be overcome by fitting a smaller jet to^the, carburettor. ;' [N.Bi-^lt-is :agaihst, regulations. to have a:straight-through exhaust on the public: highways'.] < . ■: