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 comb ...
that became obsolete after
World War I
World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting to ...
. 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 ...
distinguished from the 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 Cam-in-block, engine block, instead of in the cyl ...
by its valve placement. In T-head engines, the intake valves are located on one side of the engine block and the exhaust valves on the other. When viewed from the end of the crankshaft, especially in a cutaway view, the cylinder and combustion chamber resemble a 'T', leading to the name "T-head". In contrast, an L-head engine has all valves on the same side.
Overview
The T-head engine was an early form of
crossflow cylinder head. It was relatively complex for its time, requiring separate camshafts for the intake and exhaust valves.
T-heads were typically intricate castings, necessitating blind bores for the cylinders and valve chambers. This complexity made T-head engines more expensive to produce compared to the simpler L-head (flathead) engines. Moreover, T-head engines were heavy and inefficient for their displacement, producing less horsepower than a
flathead or modern
overhead valve
An overhead valve engine, abbreviated (OHV) and sometimes called a pushrod engine, is a piston engine whose valves are located in the cylinder head above the combustion chamber. This contrasts with flathead (or "sidevalve") engines, where the v ...
engine of comparable size.
One reason for the T-head design's popularity from the late 19th century to the 1920s was the type of
gasoline
Gasoline ( North American English) or petrol ( Commonwealth English) is a petrochemical product characterized as a transparent, yellowish, and flammable liquid normally used as a fuel for spark-ignited internal combustion engines. When for ...
available then, which ignited at lower temperatures than contemporary fuels. If gasoline vapor became too hot or was overly compressed, it risked pre-ignition 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 ...
before the spark plug could ignite it. Detonation, a leading cause of catastrophic engine failure, necessitated managing both the temperature and compression of the highly volatile gasoline vapor for maximum reliability.
The T-head addressed these issues by placing the valves in open alcoves on opposite sides of the
cylinder head
In a piston engine, the cylinder head sits above the cylinders, forming the roof of the combustion chamber. In sidevalve engines the head is a simple plate of metal containing the spark plugs and possibly heat dissipation fins. In more modern ...
. Additionally, cool water from the radiator was directed over the intake valves as a further safety measure. This design minimized heat transfer from the exhaust ports and reduced the engine's
compression ratio
The compression ratio is the ratio between the maximum and minimum volume during the compression stage of the power cycle in a piston or Wankel engine.
A fundamental specification for such engines, it can be measured in two different ways. Th ...
, thereby preventing detonation. The relative inefficiency of the T-head engine was offset by significant reliability gains and suited the lower travel and racing speeds of the era.
With the entire cylinder bore and cooling passages often contained within the head, many T-head engines required no head gasket and fewer gaskets overall, reducing potential leakage. This reliability made T-head engines popular in early auto racing, where engine reliability was more crucial than peak performance. However, as other engine designs enhanced their reliability during World War I, the T-head's performance limitations led to its decline in racing applications.
Obsolescence
The T-head engine became obsolete in passenger cars due to advancements made during
World War I
World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting to ...
and the introduction of anti-knock compounds like
tetraethyl lead
Tetraethyllead (commonly styled tetraethyl lead), abbreviated TEL, is an organolead compound with the formula Pb( C2H5)4. It was widely used as a fuel additive for much of the 20th century, first being mixed with gasoline beginning in the 192 ...
in the early 1920s. These developments made
flathead L-head engines equally reliable, while also being more powerful, lighter, more fuel-efficient, and cheaper to manufacture. Despite this, T-heads remained in use in heavy equipment, large trucks, and fire trucks, being phased out of production only in the 1950s.
Examples
This engine type was found on cars like
Mercedes and
Stutz
The Stutz Motor Car Company was an American automobile Automotive industry, manufacturer based in Indianapolis, Indiana that produced high-end Sports cars, sports and Luxury vehicle, luxury cars. The company was founded in 1911 as the Idea ...
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 Automotive industry, motor vehicle manufacturer based in Buffalo, New York, active from 1901 to 1938. Although best known for its expensive Luxury vehicle, luxury cars, Pierce-Arrow also manuf ...
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 produced T-head engines for their fire engines until the 1950s.
References
{{Reflist
Cam-in-block valvetrain configurations
Cylinder head
Engine technology
Engine valvetrain configurations
Piston engines