What are the variables that influence the performance of an internal combustion engine?
Welcome to PF, Abdul.
There are dozens of them. Volumetric efficiency, piston ring sealing efficiency, ambient temperature, fuel temperature, intake air temperature, humidity, exhaust tuning, valve and spark timing, plug condition, combustion chamber shape and cleanliness (ie: carbon build-up), port matching, atmospheric pressure, bearing friction, windage drag...
Really, it's too extensive a list to make any sense. Each issue has to be addressed individually.
Indeed. Fred's list is good, but is still only about a tenth of all the variables.
Can you be more specific with your question?
Separate names with a comma.