MY CORSA 1.6 rectified engine

Hello community, I make a consultation, I have a 2007 Chevrolet Corsa, I made the engine again, rectified and it was very good, the mechanic tells me to make 6,000km to settle it to just use it in CNC, the theme is as follows, I before making the rectification had an approx consumption. 10km per liter of gasoline, now that the new engine is consuming as 4km or 5km per liter of gasoline and it is being a fortune. Does anyone know if I can use it in CNC?