How Stuff Works
‘V’ form engines
’The vee allows the crankshaft – and therefore the engine – to be shorter’
The race for pace while saving space, as explained by our resident tech guru
One maxim has held sway throughout the history of the motor car – if you want more output, add more cylinders. The earliest internal combustion cars featured single- and twin-cylinder engines, but the four-pot lump quickly became the norm.
Meanwhile, daredevil engineers and drivers were strapping large, multicylinder aero engines to leviathan ladder chassis and punting themselves off into potential oblivion in the quest for more power and greater speed.
The trouble with these engines was that they were of a linear format, with six, eight, 12 and more cylinders, all in a line, attached to one hefty crankshaft. That’s not to say that smaller capacity engines were not being produced with cylinders in multiples greater than four. Indeed, there have been some splendid little sub-1600cc six-plus cylinder motors.
Anyway, it was not desirable to have a very long crankshaft, because it was nigh-on impossible to fi t it all in; it was better to have something shorter, more compact and with greater potential prowess than a long one, while fi tting into the allocated space.
Vee format engines allowed crankshafts, and therefore engines, to be shorter by effectively allowing the ‘overlapping’ of cylinders.
Take a V8 engine, for instance; the cylinders are separated into two banks of four cylinders angled apart by a number of degrees in a ‘vee’ formation, with the pistons connected to a common crankshaft.
In such a case, number one cylinder left and number one cylinder right could have common big end journals, either between main bearings one and two on fi ve-bearing engines, or next to the common big end journal for number two left and number two right, in the case of three-bearing engines.
Thus, if regarded in linear formation, the cylinders on such an engine would have overlapped, but the vee banks allowed the crankshaft to be short and so the engine was compact, with only, say, a 25 per cent increase in length over an example with half the number of cylinders. This, of course, depended on the number of cylinders used; veetwin engines had little difference in length to their linear counterparts.
Vee formation crankshafts could take different formations, with advantages for each in acceleration and deceleration speeds, or engine balance and the need for counterbalancing.
Typically, V8 engines fell into flat-plane or cross-plane formats; flatplane was where each cylinder bank operated like a typical linear fourcylinder engine, with the first and last cylinders of one bank rising together as the centre two fell. Flat-plane V8s were revvy, but prone to vibration.
Cross-plane V8s had their big end journals set at 90 degrees, when viewed along the crankshaft. Heavy counterbalancing allowed these engines to be smooth, but with a greater mass crankshaft, the advantage of rapid reaction was reduced.
As larger vee formation engines were squat, with good design they could be placed low and more centrally within the wheelbase than a linear equivalent, allowing an altogether better handling package to be produced, while kicking out oodles of power.