- T-Head and L-Head
Engines are sometimes classified by (1) the shape of their combustion chambers, or (2) by a description or position of the valves that allow for the delivery of the fuel/air mixture to the cylinder for combustion and the exhaust of the products of combustion away from the cylinder.
The very first engines used designs wherein the intake (fuel/air mixture) to the cylinder and the exhaust (products of combustion) from the cylinder, were accomplished through valves positioned on the sides of the cylinders. There were several variations of this type of engine design including the T-Head Engine and the L-Head Engine .
The Valve-In-Head Engine design, as the name describes, used a design wherein the intake (fuel/air mixture) to the cylinder and the exhaust (products of combustion) from the cylinder, were accomplished through valves positioned on the top or “head” of the cylinders.
The Nailhead Engine received its name from the shape of the intake/exhaust valves. The valves had a long stem and a relatively small diameter base, resembling a carpenter nail.
The HEMI Engine received its name from the shape of its cylinder head and combustion chamber. The head and chamber resembled a HEMIsphere, or a half sphere.
In 1901/02 David Buick formed his Buick Manufacturing Company with the purpose of manufacturing marine and farm engines. Buick re-hired Walter Marr, and hired a new employee, a machinist named Eugene C. Richards. The three men designed and built an engine with the intake/exhaust valves positioned on the top, or head of the engine. This was a radical design concept in the United States at that time, although Richards, an immigrant from Europe stated years later that he became familiar with this particular engine design while designing and building engines in Europe. Nevertheless, Richards applied for and was granted the United States patent for the Valve-In-Head engine design.
The T-Head and L-Head engines were so named because the shape of their combustion chambers resembled the letters “T” and “L” respectively. These engines were also known as “Flathead” engines because the top or “head” of the engine was flat.
Technically, the Valve-In-Head engine proved to be superior in performance to other engine designs of the day in regards to both efficiency and power. There are two reasons for this superiority. One reason is better fluid dynamics and the second reason is better spark-induced flame propagation.
Fluid Dynamics. The amount of horsepower required by the engine to draw into the cylinder the fuel/air mixture, produced by the carburetor, and then exhaust the products of combustion from the cylinder was much less in the Valve-In-Head engine. This was because the pathway for the fluids to travel was simpler and smoother with less sharp corners to pass through, thus reducing fluid turbulence and friction as compared to the T-Head and L-Head and other similarly designed engines. Simply put, the Valve-In-Head engine could breathe (inhale and exhale) much easier and with less effort than other designed engines.
Spark-Induced Flame Propagation. When the piston compresses the fuel/air mixture in the cylinder into the combustion chamber, the spark fires, an explosion occurs, and the piston is forced down, transforming chemical energy into mechanical power through the piston to the crankshaft/transmission/wheels. At the moment of spark, a flame propagates throughout the cylinder combustion chamber. The less distance the flame has to travel, the faster the flame ignites the fuel/air mixture and the more complete the burn (this results in better fuel efficiency and less pollutants in the form of unburned fuel exhausted). The Valve-In-Head engine has a more compact combustion chamber, thus allowing the flame to propagate across it fast and a thorough burn occurs. The elongated combustion chambers of the T-Head and L-Head engines do not allow for fast flame propagation and a thorough burn of the fuel/air mixture does not occur. The L-Head engine has the spark plug installed away from the cylinder chamber and above the intake/exhaust ports – a very bad design..
The Valve-In-Head engine was more expensive and more complicated to manufacture, than the T-Head and L-Head engines because it required more parts. More parts, of course initially also meant more maintenance. However, another major advantage of the Valve-In-Head engine was its ability to win car races and “Hill Climbing” contests. The public took notice of this superior Buick automobile, powered by its technologically advanced engine. The Buick automobile was the number one selling car in the United States in 1908 with 8,820 cars sold, more than its two closest rivals, Ford and Cadillac, combined.
The Nailhead Engine was the first V8 engine produced by Buick Motor Division of General Motors. It replaced the famous Buick “Straight Eight” engine.
The name Nailhead was a nickname given to the engine by service mechanics and technicians because the valve resembled a nail (when compared to other engine valves of that time period) with a long stem and small diameter base. The reason for this specific valve design was probably to accommodate the positioning of the spark plug. The spark plug was centered directly inline with the cylinder axis at the very top of the combustion chamber. This design provided better spark-induced flame propagation than previous engine designs that positioned the spark plug off-center.
Buick produced this engine from 1953-1966.
1953-1956: Two size engines were produced – 264 CID 4.7L and 322 CID 5.3L.
1957 – 1966 Several size engines were produced, ranging from – 364 CID 6.0L to 425 CID 7.0L.
The Hemi Engine received its name from the shape of its cylinder head which was a half sphere or hemisphere.
The idea of a hemispherical combustion chamber dates back a few hundred years to the days of cannons that fired round or spherical cannon balls. The application of hemispherical combustion chambers in automobile engines dates back to approximately 1900. In Europe, Daimler, Peugeot, and Stutz used the hemispherical combustion chamber design in their engines as early as 1912. Ford offered Hemi-engines in 1947. Chrysler Corporation started offering Hemi engines in it cars in the 1950’s. Chrysler was a big proponent of Hemi engines, trademarking the name “Hemi” in the 1960’s and using it extensively in its advertising. Buick has never offered a Hemi engine in its automobiles.
A disadvantage of the Hemi engine is when to achieve the desired higher compression ratios Hemi engine piston heads were doomed resulting in a combustion chamber resembling a “thick peel of half an orange.” This produced two negative effects on engine power output and emissions, (1) Flame propagation time increased, and (2) the forces produced by the explosion on the doomed piston head were not totally directed along the cylinder y-axis – an x-axis force component wasted energy and reduced engine power. Redesigns for the Hemi engine produced a cylinder head or combustion chamber that was no longer shaped like a hemisphere but had evolved to be shaped like a “kidney bean” with two small combustion chambers per cylinder. By 1980 serious development on the Hemi engine ceased, yielding to more emission efficient engines. Today the Hemi name is a trademark used for advertising and not descriptive of the engine’s combustion chamber.