An inline four engine is a type of internal combustion engine with four cylinders arranged in a row along the crankshaft. Sometimes called a 'straight four' or an 'L4' (the 'L' is for longitudinal, and causes less confusion than an 'I' might), the configuration is known for having almost perfect primary balance, and being very simple mechanically. the most famous inline 4 used in F1 is the BMW M12.