1 As a gen­eral rule, the longer the ex­haust and the larger the di­am­e­ter, the more power it will make at lower revs. On the flip side, smaller bore and shorter sys­tems will pro­mote a grun­tier mo­tor. 2 Back pres­sure be­ing ben­e­fi­cial on a four-stroke sys­tem is a fal­lacy. In re­al­ity, you don’t want an ex­haust to cre­ate any re­stric­tion to gas flow, as this will com­pro­mise per­for­mance. The only caveat is the ad­di­tion of ex­haust but­ter­fly valves, as these are de­signed to fill-in torque deficits on sys­tems that are tuned for high end power. 3 Un­like race cans, which are es­sen­tially per­fo­rated tubes wrapped in sound dead­en­ing ma­te­rial, road le­gal equiv­a­lents utilise specif­i­cally cal­cu­lated cham­ber sizes to elim­i­nate spe­cific sound fre­quen­cies. 4 Cat­alytic con­vert­ers con­tain pre­cious met­als that pro­mote the con­ver­sion of toxic pol­lu­tants gases into harm­less gases, such as switch­ing car­bon monox­ide into car­bon diox­ide (and wa­ter). 5 While ti­ta­nium, stain­less and mild steel are com­monly used in ex­haust pro­duc­tion, light­weight alu­minium isn’t ca­pa­ble of with­stand­ing the high tem­per­a­tures present in ex­haust gases (up to 700ºC). Some very high per­for­mance race en­gines ex­ceed this tem­per­a­ture and re­quire sys­tems made from nickel based al­loys.

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