the preferred embodiment serve two complementary functions firstly in providing the rough texture of the inner surface 12b of the tube 12 and secondly in facilitating the use of helical spring elements 30 as the means for retaining the flow disturber 20 in position within the tube 12 the effectiveness of the present invention in reducing pollutant emissions in vehicle exhaust has been demonstrated by tests using a number of motor vehicles generally speaking the characteristics of exhaust emissions from vehicle engines will vary according to a number of factors including engine displacement type of fuel used i e gasoline or diesel and whether the engine is carbureted or fuel injected in tests performed using a 34 snap on 34 brand emission testing machine the hydrocarbon 34 hc 34 and carbon monoxide 34 co 34 emissions measured in parts per million or 34 ppm 34 for a variety of engines equipped with the present invention and operating at low speeds were observed to have been reduced as summarized in the following table ______________________________________ hc covehicle description ppm ppm ______________________________________1980 dodge 360 c i v 8 carbureted gas without agitator 154 3 58with agitator 131 2 981989 buick 3 8 l v 6 fuel injected gas without agitator 338 0 93with agitator 300 0 261990 chevrolet6.