Tuneable tuned pipe exhaust system

Tuneable means for the exhaust system of a two-stroke cycle internal combustion engine, comprising a baffle slidable longitudinally within an exhaust pipe of said exhaust system;

• a plug insertable into the free, downstream end of said exhaust pipe;
• and means for selectively positioning said baffle within said exhaust pipe to thereby define therein an upstream primary chamber and a downstream secondary chamber;
• said baffle having a wave-reflecting upstream side constituted by a concavity of substantially conical configuration, having a conic angle of 30.degree., the apex of the concavity leading into a manifold chamber from which radiate a plurality of spaced passageways, each inclined towards said secondary chamber, which communicate said primary chamber with said secondary chamber, the combined cross-sectional area of the exhaust port of the engine's manifold;
• said plug having a wave-reflecting upstream side constituted by a concavity of substantially conical configuration, having a conic angle of 30.degree., the apex of the concavity leading into a chamber from which a passageway, inclined away from said secondary chamber, communicates said secondary chamber with atmosphere, the cross-sectional area of said passageway being 13% of the cross-sectional area of the exhaust port of the engine's manifold;
• and said baffle positioning means including an elongated rod, one end of which is inserted into the apex of a substantially conical boss forming the downstream side of said baffle and the other end of which is adapted to extend through a co-acting bore extending longitudinally through said plug;
• said plug being provided with screw and locknut combination means to immobilize said elongated rod in said bore to thereby immobilize said baffle at a selected location within said exhaust pipe, there being stop means on said rod to prevent said baffle from approaching said plug so closely as to inhibit exhaust discharge.

Tuneable means for the exhaust system of a two-stroke cycle internal combustion engine, comprising a baffle slidable longitudinally within an exhaust pipe of said exhaust system;

• a plug insertable into the free, downstream end of said exhaust pipe;
• and means for selectively positioning said baffle within said exhaust pipe to thereby define therein an upstream primary chamber and a downstream secondary chamber;
• said baffle having a wave-reflecting upstream side constituted by a concavity of substantially conical configuration, having a conic angle of 30.degree., the apex of the concavity leading into a manifold chamber from which radiate a plurality of spaced passageways, each inclined towards said secondary chamber, which communicate said primary chamber with said secondary chamber, the combined cross-sectional areas of said four passageways being 25% of the cross-sectional area of the exhaust port of the engine's manifold;
• said plug having a wave-reflecting upstream side constituted by a concavity of substantially conical configuration from which lead off a plurality of spaced, axially-oriented passageways to thereby communicate said secondary chamber with atmosphere;
• and said baffle positioning means including an elongated rod, one end of which is threaded so as to be screwable into the apex of a substantially conical boss forming the downstream side of said baffle and the other end of which is adapted to extend through a co-acting bore extending longitudinally through said plug;
• said plug being provided with internal threads around the wall of the bore of the plug to co-operate with external threads on the downstream end of said elongated rod, to thereby immobilize said rod in said bore and thus to immobilize said baffle at a selected location within said exhaust pipe.