T-head engine
Encyclopedia
A T-head engine is an early type of internal combustion engine
that became obsolete after World War I
.
It is a sidevalve engine that is distinguished from the much more common L-head by its placement of the valves. The intake valves are on one side of the engine block and the exhaust valves on the other. Seen from the end of the crankshaft, in cutaway view, the cylinder and combustion chamber resembles a T - hence the name "T-head". An L-head has all valves at the same side.
. The design was very complex for its day, requiring separate camshafts to operate the intake and exhaust valves. This made the engine much more expensive to produce than a comparable L-head (flathead) engine. Additionally, it was also quite heavy and inefficient for its displacement, producing less horsepower than a flathead
or modern overhead valve
engine of comparable displacement.
The reason for this design's popularity from the turn of the 20th century into the 1920s is due to the type of gasoline
sold at the time, which ignited at a much lower temperature than modern motor fuels. If the gasoline vapor got too hot or was compressed too much it could explode before being lit by the spark plug, a condition known as engine knocking
or detonation
. Since detonation was-and still is-a primary cause of catastrophic engine failure, limiting both the temperature and compression of the extremely explosive gasoline vapor was critical for maximum engine reliability.
The T-Head addressed both of these issues by putting the valves in open alcoves on opposite sides of the cylinder head
and having cool water from the radiator enter the engine directly over the intake valves as an extra measure of safety. The heat transfer from the exhaust ports was thus minimized, and the extra volume of the open alcoves that housed the valves also lowered the effective compression ratio
of the engine. Detonation was thus eliminated, and the relative inefficiency of the engine design was offest by the dramatic reliability gains achieved and the generally lower speeds of travel and racing common to the era. This superior reliability made the design a favorite racing engine in the earliest days of auto racing, when engine reliability arguably mattered more than maximum performance. As other engine designs improved in reliability thanks to the intense engine development done in World War I
, the T-head's inherent compromises in performance caused it to rapidly fall out of favor for racing applications.
and the introduction of effective anti-knock compounds such as tetra-ethyl lead
in the early 1920s. When combined, these advances made flathead
engines just as reliable as T-heads while also being more powerful, lighter, more fuel efficient, and cheaper to manufacture.
The T-heads' incredible reliability did however keep them in service in heavy equipment, large trucks, and fire trucks until they were finally phased out of production in the 1950s.
and Stutz
and the last T-head engine in production for personal cars was manufactured by an American company, Locomobile, around 1920. American LaFrance
produced T-head engines in their fire engines until the 1950s, though they did build overhead-cam engines in the 1940s.
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
that became obsolete after World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...
.
It is a sidevalve engine that is distinguished from the much more common L-head by its placement of the valves. The intake valves are on one side of the engine block and the exhaust valves on the other. Seen from the end of the crankshaft, in cutaway view, the cylinder and combustion chamber resembles a T - hence the name "T-head". An L-head has all valves at the same side.
Overview
This was an early form of crossflow cylinder headCrossflow cylinder head
A crossflow cylinder head is a cylinder head that features the intake and exhaust ports on opposite sides. The gases can be thought to flow across the head...
. The design was very complex for its day, requiring separate camshafts to operate the intake and exhaust valves. This made the engine much more expensive to produce than a comparable L-head (flathead) engine. Additionally, it was also quite heavy and inefficient for its displacement, producing less horsepower than a flathead
Flathead engine
A flathead engine is an internal combustion engine with valves placed in the engine block beside the piston, instead of in the cylinder head, as in an overhead valve engine...
or modern overhead valve
Overhead valve
An overhead valve engine, also informally called pushrod engine or I-head engine, is a type of piston engine that places the camshaft within the cylinder block , and uses pushrods or rods to actuate rocker arms above the cylinder...
engine of comparable displacement.
The reason for this design's popularity from the turn of the 20th century into the 1920s is due to the type of gasoline
Gasoline
Gasoline , or petrol , is a toxic, translucent, petroleum-derived liquid that is primarily used as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. Some gasolines also contain...
sold at the time, which ignited at a much lower temperature than modern motor fuels. If the gasoline vapor got too hot or was compressed too much it could explode before being lit by the spark plug, a condition known as engine knocking
Engine knocking
Knocking in spark-ignition internal combustion engines occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front.The...
or detonation
Engine knocking
Knocking in spark-ignition internal combustion engines occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front.The...
. Since detonation was-and still is-a primary cause of catastrophic engine failure, limiting both the temperature and compression of the extremely explosive gasoline vapor was critical for maximum engine reliability.
The T-Head addressed both of these issues by putting the valves in open alcoves on opposite sides of the cylinder head
Cylinder head
In an internal combustion engine, the cylinder head sits above the cylinders on top of the cylinder block. It closes in the top of the cylinder, forming the combustion chamber. This joint is sealed by a head gasket...
and having cool water from the radiator enter the engine directly over the intake valves as an extra measure of safety. The heat transfer from the exhaust ports was thus minimized, and the extra volume of the open alcoves that housed the valves also lowered the effective compression ratio
Compression ratio
The 'compression ratio' of an internal-combustion engine or external combustion engine is a value that represents the ratio of the volume of its combustion chamber from its largest capacity to its smallest capacity...
of the engine. Detonation was thus eliminated, and the relative inefficiency of the engine design was offest by the dramatic reliability gains achieved and the generally lower speeds of travel and racing common to the era. This superior reliability made the design a favorite racing engine in the earliest days of auto racing, when engine reliability arguably mattered more than maximum performance. As other engine designs improved in reliability thanks to the intense engine development done in World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...
, the T-head's inherent compromises in performance caused it to rapidly fall out of favor for racing applications.
Obsolescence
The T-head was rendered obsolete in the passenger car market by a combination of engine advances made in World War IWorld War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...
and the introduction of effective anti-knock compounds such as tetra-ethyl lead
Tetra-ethyl lead
Tetraethyllead , abbreviated TEL, is an organolead compound with the formula 4Pb. An inexpensive additive, its addition to gasoline from the 1920's allowed octane ratings and thus engine compression to be boosted significantly, increasing power and fuel economy...
in the early 1920s. When combined, these advances made flathead
Flathead engine
A flathead engine is an internal combustion engine with valves placed in the engine block beside the piston, instead of in the cylinder head, as in an overhead valve engine...
engines just as reliable as T-heads while also being more powerful, lighter, more fuel efficient, and cheaper to manufacture.
The T-heads' incredible reliability did however keep them in service in heavy equipment, large trucks, and fire trucks until they were finally phased out of production in the 1950s.
Examples
This engine type was found on cars like MercedesMercedes (car)
Mercedes was a brand of the Daimler-Motoren-Gesellschaft . DMG which began to develop in 1900, after the death of its co-founder, Gottlieb Daimler...
and Stutz
Stutz Motor Company
The Stutz Motor Company was a producer of luxury cars based in Indianapolis, Indiana, USA. Production began in 1911 and continued through 1935. The marque reappeared in 1968 under the aegis of Stutz Motor Car of America, Inc., and with a newly defined modern retro-look. Although the company is...
and the last T-head engine in production for personal cars was manufactured by an American company, Locomobile, around 1920. American LaFrance
American LaFrance
American LaFrance is an emergency and vocational vehicle manufacturer, currently based in Summerville, South Carolina. Focusing primarily on emergency apparatus fire engines and fire aerial including ambulance and rescue vehicles.-History:...
produced T-head engines in their fire engines until the 1950s, though they did build overhead-cam engines in the 1940s.