| the rapid increase of the technological development, makes automakers produce vehicles that refers to two main characteristics, especially on combustion engine, including high performance and low exhaust gas emissions. One way is to utilize the hydrogen from the catalyst reaction of steam with the use of Hydrocarbon Crack System (HCS). Hydrogen vapors that are drawn through to the intake manifold to combustion chamber and improve the combustion process. Research conducted in the thesis aims to determine the use of HCS in four stroke engine single cylinder. This type of the result, this type of the research is carried out experimental studies. Way to resolving the result is to compare the power, torque, specific fuel consumption, and exhaust gas emissions before and after the use of HCS. the result showed increase after the use of HCS. the result showed an increase after the use of HCS maximum torque of 7,04 %, and increase maximum power 4.32 % at maximum power, specific fuel consumption decrease by 75,8 %, average level, from the average of average CO and average HC, respectively decrease by 5,5% and 4,4 %, and actual AFR is closed to stoichiometric AFR to equal 1,007. |