A process to adjust the ignition timing of an air-fuel mixture in a combustion chamber of an internal combustion engine , the process comprising the steps of a. determining a first quantity indicative of a pressure of the mixture for a cycle of the engine, b. determining a second quantity indicative of a speed of the engine , c. determining a third quantity indicative of a first temperature of a conditioning fluid used to thermally condition the combustion chamber at a zone of heat exchange between the engine and the conditioning fluid, d. providing a heat exchange mathematical model for the combustion chamber , the model mapping the set of three quantities, consisting of the first, the second and the third quantity, onto a fourth quantity indicative of a second temperature of a wall portion of the engine around the combustion chamber , e. estimating the fourth quantity by means of the three determined quantities and by means of the mathematical model, and f. adjusting the ignition timing as a function of the fourth estimated quantity, characterized in that the mathematical model maps said three quantities onto the fourth quantity by means of a numerical integration of a heat flow flowing through the wall portion , the heat flow being modelled as a flow resulting from the presence of a first and a second heat flow modelled as respective products of a first and a second heat exchange coefficient, with a first and a second temperature difference respectively, wherein - the first temperature difference is between the second temperature and a third temperature of the mixture corresponding to said pressure; and - the second temperature difference is between the first temperature and the second temperature, and/or in that step f comprises the steps of f1. determining the second temperature by means of the fourth quantity, f2. determining a fifth quantity indicative of a relationship between the second temperature and a fifth reference or calibration temperature for the wall portion , and f3. adjusting the ignition timing depending on the fifth quantity. a. determining a first quantity indicative of a pressure of the mixture for a cycle of the engine, b. determining a second quantity indicative of a speed of the engine , c. determining a third quantity indicative of a first temperature of a conditioning fluid used to thermally condition the combustion chamber at a zone of heat exchange between the engine and the conditioning fluid, d. providing a heat exchange mathematical model for the combustion chamber , the model mapping the set of three quantities, consisting of the first, the second and the third quantity, onto a fourth quantity indicative of a second temperature of a wall portion of the engine around the combustion chamber , e. estimating the fourth quantity by means of the three determined quantities and by means of the mathematical model, and f. adjusting the ignition timing as a function of the fourth estimated quantity, - the first temperature difference is between the second temperature and a third temperature of the mixture corresponding to said pressure; and - the second temperature difference is between the first temperature and the second temperature, and/or in that step f comprises the steps of f1. determining the second temperature by means of the fourth quantity, f2. determining a fifth quantity indicative of a relationship between the second temperature and a fifth reference or calibration temperature for the wall portion , and f3. adjusting the ignition timing depending on the fifth quantity. and/or in that step f comprises the steps of f1. determining the second temperature by means of the fourth quantity, f2. determining a fifth quantity indicative of a relationship between the second temperature and a fifth reference or calibration temperature for the wall portion , and f3. adjusting the ignition timing depending on the fifth quantity. <EOS>