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The automobile industry presently focuses on improving fuel economy and reducing the weight of vehicles. One part of these efforts is to develop high-performance engines for improved combustion efficiency and lower emissions. Against this background, many high-performance motorcycle engines use forged pistons made of extruded or continuously cast aluminum alloy for high reliability and material properties. The cost of forged pistons is higher than that of gravity die cast pistons. To replace these expensive forged pistons, a low-cost, high-performance piston with increased endurance and thermal resistance has been developed using a newly developed aluminum alloy and a high-quality die casting technology using an oxygen supply system and additional pressure.

A calculation method of the bore distortion during engine operation was developed. This method can consider the sliding effect of the cylinder head on the top dock of the cylinder block. The bore distortion during engine operation calculated by this method agrees with that measured by Fujimoto, better than that calculated by conventional method. Calculated results for a Toyota 4-cylinder in-line 1.5L engine showed that thermal distortion has larger effects on the cylinder bore distortion during engine operation than cylinder head clamping distortion.

Fuel and air behavior in the induction passage of a 4-valve engine were investigated in order to improve response at low and medium engine speeds. It was found that response is affected not only by wall vetting but also by fuel being pushed back into the intake manifold and by a lack of fuel which occurs during the transient. Futhermore, fuel-air mixing was found to be insufficient at certain injection timings, resulting in poor combustion and a consequent increase in exhaust emission and fuel consumption. This paper describes the factors of the fuel injection system which are critical for optimum response. Recommendations are made for injector location and injection timing and a proposal is put forward for a system of compensatory fuel injection to improve combustion efficiency during acceleration.