What is valves on cars?

Valves control the in-flow and out-flow of fuel, air and exhaust fumes in a combustion engine (known as intake valves and exhaust valves). A 4-cylinder engine with 16 valves will have 4 valves per cylinder, with two intake and two exhaust valves per cylinder. With experience it is easy to tell the sounds of the valves apart because each engine sounds different with different valves.

Generally the less number of valves means a deeper/throatier sound from the cars and vice-versa