It's normaly down to
A) The orignal vehicle the engine line was designed for and how it would fit.
B) The engine designer having no constraints and opting for either option.
You can get all combinations of inlet and exhaust being on the same side and on opposing sides.
On opposing sides the engine is termed a crossflow design, hence the original kent engine which had an "inlet over exhaust" design was redesigned with inlet on one side exhaust on the other and from then on was known as the X-Flow .
I-O-E are still quite common, many VW Big Block engines are like this, makes them a bit pants on side draught carbs as the suck in exhaust heat.
TT
|