T-head Engine
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A T-head engine is an early type of
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combus ...
that became obsolete after
World War I World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...
. It is a
sidevalve engine A flathead engine, also known as a sidevalve engine''American Rodder'', 6/94, pp.45 & 93. or valve-in-block engine is an internal combustion engine with its poppet valves contained within the engine block, instead of in the cylinder head, as ...
that is distinguished from the much more common
L-head A flathead engine, also known as a sidevalve engine''American Rodder'', 6/94, pp.45 & 93. or valve-in-block engine is an internal combustion engine with its poppet valves contained within the engine block, instead of in the cylinder head, as ...
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 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. This is in contrast to reverse-flow cylinder head designs that have the ports on the same ...
. The design was fairly complex for its day, requiring separate camshafts to operate the intake and exhaust valves. The T-heads themselves were typically complex castings requiring blind bores for the cylinders and valve chambers. This made the engine 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 An overhead valve (OHV) engine, sometimes called a ''pushrod engine'', is a piston engine whose valves are located in the cylinder head above the combustion chamber. This contrasts with earlier flathead engines, where the valves were located be ...
engine of comparable displacement. The reason for this design's popularity from the turn of the 20th century into the 1920s was the type of
gasoline Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organic co ...
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 In spark ignition internal combustion engines, knocking (also knock, detonation, spark knock, pinging or pinking) occurs when combustion of some of the air/fuel mixture in the cylinder does not result from propagation of the flame front ignite ...
or
detonation Detonation () is a type of combustion involving a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations propagate supersonically through shock waves with ...
. 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 In an internal combustion engine, the cylinder head (often abbreviated to simply "head") sits above the cylinders and forms the roof of the combustion chamber. In sidevalve engines, the head is a simple sheet of metal; whereas in more modern ov ...
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 The compression ratio is the ratio between the volume of the cylinder and combustion chamber in an internal combustion engine at their maximum and minimum values. A fundamental specification for such engines, it is measured two ways: the stati ...
of the engine. Detonation was thus eliminated, and the relative inefficiency of the engine design was offset by the dramatic reliability gains achieved and the generally lower speeds of travel and racing common to the era. In addition with the entire cylinder bore and all cooling passages frequently contained within the head many t-head engines required no head gasket and relatively few gaskets of any kind, reducing potential leakage. 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 (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...
, 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 I World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...
and the introduction of effective anti-knock compounds such as
tetraethyl lead Tetraethyllead (commonly styled tetraethyl lead), abbreviated TEL, is an organolead compound with the formula Pb( C2H5)4. It is a fuel additive, first being mixed with gasoline beginning in the 1920s as a patented octane rating booster that al ...
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.


Examples

This engine type was found on cars like Mercedes and Stutz and the last T-head engine in production for personal cars was manufactured by an American company, Locomobile. Stutz and White Motor Car Company both used four valve engines in 1917, developing 65 and 72 horse power respectively. The White Company engine was a mono block design. The
Pierce-Arrow The Pierce-Arrow Motor Car Company was an American motor vehicle manufacturer based in Buffalo, New York, which was active from 1901 to 1938. Although best known for its expensive luxury cars, Pierce-Arrow also manufactured commercial trucks ...
company introduced a production four-valve per cylinder T-head motor (Dual Valve Six) in 1918, one of the few, perhaps the only, multi-valve valve-in-block type engines produced.
American LaFrance American LaFrance (ALF) was an American vehicle manufacturer which focused primarily on the production of fire engines, fire aerials, and emergency apparatus such as ambulance and rescue vehicles. Originally located in Elmira, New York, the fi ...
produced T-head engines for their fire engines until the 1950s, though they also built overhead-cam engines in the 1940s. {{Commons cat, T-head engines Cam-in-block valvetrain configurations Cylinder head Engine technology Engine valvetrain configurations Piston engines