In the main java folder of the car change the name to engine you want.
This is the one from the Focer Java.
public void addStockParts( Descriptor desc )
{
// stock 1 stuffs //
stock_parts_list_E = new int[2];
stock_parts_list_E[ 0] = parts.engines.Einvagen_Duhen_Ishima_Focer:0x000000F9r; // "Shimutshibu RC B95S200 2.0L I4" //
stock_parts_list_E[ 1] = parts:0x000053FFr; // "stock battery" //