Hello everyone, this is my first contribution in this forum, I'm aware that this question had been asked many times either in this forum or elsewhere and I have indeed read at least one thread with a similar topic, however, unfortunately, I have yet to find specific answers that nail the core fundamentals in a solid means, that's why I preferred to post this thread separately rather than bumping up an older thread in hope it will be more focused on the subject this time. How does the action of the accelerator pedal changes the rpm of the internal combustion engine ? And which quantities are or should be* constant and which are variable through the whole rpm range (e.g from idle to red line) as the engine accelerates when pressing the pedal ? 1- Compression ratio 2- Air to fuel ratio 3- Ignition rate 4- Air flow rate through intake manifold Please note that : - This subject is beyond the basic fundamentals that describe the primary functions and terminology of internal combustion engine and their theoretical cycles. - *: In general I'm not referring to an absolute constant quantity, so if there would be any variation that is not controllable or not meant to regulate the engine speed (rpm) then this should not be considered in the explanation, such variations are the resultant of thermal deficiencies or mechanical friction.