Petrol Fuel Engine

The two most common valve arrangements are :
(1) L-head
(2) I-head

An L-head, or underhead, valve engine has the intake and exhaust valves side by side in the cylinder block. The intake valve admits the air-fuel mixture into the cylinder and the exhaust valve lets out the exhaust gases. An I-head, or overhead, valve engine has the two valves side by side in the cylinder head, the cylinder block's top cover. In some cars, each cylinder has four valves--two intake valves and two exhaust valves