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Flat-eight engine
A flat-eight engine (also known as a horizontally-opposed eight) is an eight-cylinder piston engine with two banks of four inline cylinders, one on each side of a central crankshaft, 180° apart.
In a flat-eight engine, the connecting rods for corresponding pistons from the left and right banks may share a crankshaft journal. A boxer-eight engine is a special case of a flat-eight where each piston's connecting rod has its own journal, and each pair of opposed pistons moves inwards or outwards at the same time.
Flat-eight engines have been used in automotive, motorcycle, aircraft, and marine applications.
The advantages of a flat-eight engine are its minimal length and low centre of mass. A disadvantage is its greater width compared to a V8 or inline-eight engine. A flat-eight engine is able to have perfect primary balance and secondary balance.
A boxer-eight engine has a single piston per crankpin, which increases the linear offset between the cylinder banks. A boxer-eight with nine main bearings may be thought of as two boxer-four engines laid end-to-end with a 90° phase angle between their crankshafts.
Alternatively, a flat-eight engine where corresponding pistons from the two opposing banks share a crankshaft journal is often called a "180 degree V engine". One possible configuration for this design uses a two-plane crankshaft. Another configuration uses a 180° single-plane crankshaft with the leading and trailing crankpins in the same position, while the two central crankpins are in the opposite position.
One of the earliest flat-eight engines was used in the 1904 Buffum Model G Greyhound racing car, which used an engine based on two of Buffum's existing flat-four engines joined together. The Model G was built in the United States and was introduced one year after the Winton Motor Carriage Company Bullet No. 2, which used a straight-8 engine. Around the same time, the first V8 engines were beginning to appear in Europe.
Several racing cars have used bespoke flat-eight engines based on two inline-four engines and a custom crankshaft. These include the 1928 Anderson Specials Number 2 built in Scotland using two Humber 9/20 engines. The car is on display at the Kelvingrove Art Gallery and Museum in Glasgow. Another example is a 1977 Eagle 72 chassis raced by Bruce Crower in the United States. This engine used the cylinder heads from two Chevrolet Cosworth Vega engines. In 1969, a one-off engine was built for racing driver Emerson Fittipaldi to compete in the Thousand Miles of Guanabara endurance race. This flat-eight engine was made by joining two 1.3 L Volkswagen flat-four crankcases with an elastomeric gasket and connecting the two crankshafts together. Several similar Volkswagen-based engines were built for Fittipaldi's racing cars in the early 1970s.
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Flat-eight engine
A flat-eight engine (also known as a horizontally-opposed eight) is an eight-cylinder piston engine with two banks of four inline cylinders, one on each side of a central crankshaft, 180° apart.
In a flat-eight engine, the connecting rods for corresponding pistons from the left and right banks may share a crankshaft journal. A boxer-eight engine is a special case of a flat-eight where each piston's connecting rod has its own journal, and each pair of opposed pistons moves inwards or outwards at the same time.
Flat-eight engines have been used in automotive, motorcycle, aircraft, and marine applications.
The advantages of a flat-eight engine are its minimal length and low centre of mass. A disadvantage is its greater width compared to a V8 or inline-eight engine. A flat-eight engine is able to have perfect primary balance and secondary balance.
A boxer-eight engine has a single piston per crankpin, which increases the linear offset between the cylinder banks. A boxer-eight with nine main bearings may be thought of as two boxer-four engines laid end-to-end with a 90° phase angle between their crankshafts.
Alternatively, a flat-eight engine where corresponding pistons from the two opposing banks share a crankshaft journal is often called a "180 degree V engine". One possible configuration for this design uses a two-plane crankshaft. Another configuration uses a 180° single-plane crankshaft with the leading and trailing crankpins in the same position, while the two central crankpins are in the opposite position.
One of the earliest flat-eight engines was used in the 1904 Buffum Model G Greyhound racing car, which used an engine based on two of Buffum's existing flat-four engines joined together. The Model G was built in the United States and was introduced one year after the Winton Motor Carriage Company Bullet No. 2, which used a straight-8 engine. Around the same time, the first V8 engines were beginning to appear in Europe.
Several racing cars have used bespoke flat-eight engines based on two inline-four engines and a custom crankshaft. These include the 1928 Anderson Specials Number 2 built in Scotland using two Humber 9/20 engines. The car is on display at the Kelvingrove Art Gallery and Museum in Glasgow. Another example is a 1977 Eagle 72 chassis raced by Bruce Crower in the United States. This engine used the cylinder heads from two Chevrolet Cosworth Vega engines. In 1969, a one-off engine was built for racing driver Emerson Fittipaldi to compete in the Thousand Miles of Guanabara endurance race. This flat-eight engine was made by joining two 1.3 L Volkswagen flat-four crankcases with an elastomeric gasket and connecting the two crankshafts together. Several similar Volkswagen-based engines were built for Fittipaldi's racing cars in the early 1970s.