eng Science and Education Publishing American Journal of Mechanical Engineering 2328-4110 2019-11-28 7 4 188 194 10.12691/ajme-7-4-5 AJME2019745 article Rochmad Novian Inderanata inderanata@gmail.com 1 Thomas Sukardi 1 Slamet Priyanto 2 Mechanical Engineering Education, Yogyakarta State University, Yogyakarta, Indonesia Mechanical Engineering Education, Sarjanawiyata Tamansiswa University, Yogyakarta, Indonesia On a 4-stroke engine, valve work and function have a very big influence on engine performance and characteristics. To improve engine performance, one of them is by way of bore up. This study aims to determine and compare the performance of a standard 4 stroke 105 cc engine before and after bore ups, stroke ups and the use of racing valves in testing power (P), torque (T) and fuel consumption (mf). This research method uses a 4 stroke 105 cc standard engine and a 150 cc bore up engine with a variety of standard and racing valves. The testing method uses the throttle method spontaneously from 4000 rpm to 1100 rpm and the throttle method per 1000 rpm from 4000 rpm then is increased to 8000 rpm gradually. Data taken in this study are torque (T), power (P), and fuel consumption (mf). The results showed that by changing the volume of the cylinder (bore up) by using variations of the racing valve can significantly improve engine performance. The average value of the percentage increase in torque power and fuel consumption compared to the results on a standard 4-stroke engine. On a standard 105 cc engine for 8000 rpm engine speed, 4.63 (N.m) of torque, 3.90 (kW) of power obtained and 0.879 (kg/h) of fuel consumption. In a semi racing engine at 8000 rpm, torque is 9.45 (N.m)(104,10%), power is 8.13 (kW)(108,46%) and fuel consumption is 1.118 (kg/h)(27%). In a full 150 cc racing engine for 8000 rpm engine speed the torque is 12.87 (N.m)(177,97%), the power is 10.79 (kW)(176,67) and fuel consumption is 1.116 (kg/h)(26,96%). http://pubs.sciepub.com/ajme/7/4/5/ajme-7-4-5.pdf bore up stroke up intake valve exhaust valve throttle