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A Yamaha YZ400, 5-valve, 4-stroke cycle, motocross racing, motorcycle engine is instrumented to provide pressure diagrams in the exhaust system which are recorded over the usable engine speed range at full throttle from 5000 rpm to 11000 rpm. The engine produces a maximum of some 34 kW (46 hp) power output. The production muffler-ended exhaust system is replaced with two alternative and more highly-tuned exhaust systems, namely a straight pipe and a straight pipe and diffuser. The complete engine geometry together with these two exhaust systems is simulated using an engine simulation software package (VIRTUAL 4-STROKE) and the experimentally-recorded exhaust pressure diagrams and performance characteristics of power, torque, etc., are compared with the predictions of the theoretical simulation. The variation of exhaust system produces differing performance characteristics whose origins the measured pressure diagrams and recorded performance characteristics struggle to explain.

The paper discusses briefly the development of the theory of unsteady gas flow from a position of being totally misunderstood from the turn of this century until the 1940's, developed in the 1950's, and from which juncture the advent of the digital computer has turned such theory into a comprehensive design tool by the present day. While the most extensive use of this design method is for engines with a high performance specification, its employment as a design tool for industrial engines has been largely ignored. In the paper, a design for a small generating set engine at 3600 rpm is examined in great detail and the use of pressure wave effects is shown to enhance the engine performance considerably, either in terms of power gain, reduction of fuel consumption, reduction of hydrocarbon emissions, or reduction of noise levels.

Design and Simulation of Two-Stroke Engines is a unique hands-on information source. The author, having designed and developed many two-stroke engines, offers practical and empirical assistance to the engine designer on many topics ranging from porting layout, to combustion chamber profile, to tuned exhaust pipes. The information presented extends from the most fundamental theory to pragmatic design, development, and experimental testing issues. Chapters cover: Introduction to the Two-Stroke Engine Combustion in Two-Stroke Engines Computer Modeling of Engines Reduction of Fuel Consumption and Exhaust Emissions Reduction of Noise Emission from Two-Stroke Engines and more