Cylinder head porting

Cylinder head porting is the technology of modifying the intake and exhaust ports of an internal combustion engine to improve the quality and quantity of the gas flow. Cylinder heads as manufactured cannot be optimal due to design and manufacturing constraints. Porting the heads provides the finely detailed attention required to bring the engine to the highest level of efficiency. More than any other single factor porting technology is responsible for the high power output of modern engines.

This process can be applied to a standard racing engine to optimize its power output as well as to a production engine to turn it into a racing engine, to enhance its power output for daily use or to alter its power output characteristics to suit a particular application.

Daily human experience with air gives the impression that air is light and nearly non-existent as we move slowly through it. An engine running at high speed experiences a totally different substance. In that context, air can be thought of as thick, sticky, elastic, gooey and heavy (see viscosity). Pumping it is a major problem for engines running at speed. Porting helps engines deal with this problem.

Cylinder head

In an internal combustion engine, the cylinder head sits atop the cylinders and consists of a platform containing part of the combustion chamber and the location of the valves and spark plugs. In a flathead engine, the mechanical parts of the valve train are all contained within the block, and the head is essentially a flat plate of metal bolted to the top of the cylinder bank; this simplicity leads to ease of manufacture and repair, and accounts for the flathead engine's early success in production automobiles and continued success in small engines, such as lawnmowers. This design, however, requires the incoming air to flow through a convoluted path, which limits the ability of the engine to perform at higher rpm, leading to the adoption of the overhead valve head design.

In the overhead valve head, the top half of the cylinder head contains the camshaft in an overhead cam engine, or another mechanism (such as rocker arms and pushrods) to transfer rotational mechanics from the crankshaft to linear mechanics to operate the valves (pushrod engines perform this conversion at the camshaft lower in the engine and use a rod to push a rocker arm that acts on the valve). Internally the cylinder head has passages called ports for the fuel/air mixture to travel to the inlet valves from the intake manifold, for exhaust gases to travel from the exhaust valves to the exhaust manifold, and for antifreeze (coolant) to cool the head and engine.

The number of cylinder heads in an engine is a function of the engine configuration. A straight engine has only one cylinder head. A V engine usually has two cylinder heads, one at each end of the V, although Volkswagen, for instance, produces a V6 called the VR6, where the angle between the cylinder banks is so narrow that it utilizes a single head. A boxer engine has two heads.

The cylinder head is key to the performance of the internal combustion engine, as the shape of the combustion chamber, inlet passages and ports (and to a lesser extent the exhaust) determines a major portion of the volumetric efficiency and compression ratio of the engine.

Single cylinder engine

A single cylinder engine, colloquially known as a one-lunger, is an engine configuration consisting of just one cylinder, the simplest arrangement possible for an Otto or Diesel engine. The mounting can be standing, lying or angled.


Pros and Cons

Compared to multi-cylinder engines, single cylinder engines have several advantages, primarily their simple and economical construction. Balance shafts and counterweights on the crankshaft must be used to balance the weight of reciprocating parts, and can be expensive and complicated due to the collective mass of multiple cylinders. Components such as the crank have to be just as strong as in a four-cylinder engine of the same capacity per cylinder, meaning that some parts are effectively four times heavier than they need to be for the total displacement of the engine. This leads to the biggest downside of the single cylinder engine: it develops considerably lower power to weight ratios than a multi-cylinder of the same type.


Uses

Some early automobiles, such as the Cadillac 1906 Model K and 1907 Models L and M used single-cylinder engines. Single cylinder engines were also popular at one time for marine uses. Today the most common configuration is the 50cc-two-stroke Otto seen in so many bikes and scooters. These vehicles allowed the first mass-motorisation in many countries. Most engines used in small portable appliances, such as chainsaws, generators and domestic lawn mowers, usually have one cylinder. Also, the one-lunger is used in working vehicles, motorsports, airplanes, and as an industrial motor.

Piston

In general, a piston is a sliding plug that fits closely inside the bore of a cylinder.

Its purpose is either to change the volume enclosed by the cylinder, or to exert a force on a fluid inside the cylinder.


Internal combustion engine

Most pistons fitted in a cylinder have piston rings. Usually there are two spring-compression rings that act as a seal between the piston and the cylinder wall, and one or more oil control rings below the compression rings. The head of the piston can be flat, bulged or otherwise shaped. Pistons can be forged or cast. The shape of the piston is normally rounded (but can be different, see NR500 ). A special type of cast piston is the hypereutectic piston. The piston is an important component of a piston engine and of hydraulic pneumatic systems.

In an Otto or Diesel engine, the head of the piston forms one wall of an expansion chamber inside the cylinder. The opposite wall, called the cylinder head, contains inlet and exhaust valves for gases.

As the piston moves inside the cylinder, it transforms the energy from the expansion of a burning gas (usually a mixture of petrol or diesel and air) into mechanical power (in the form of a reciprocating linear motion). From there the power is conveyed through a connecting rod to a crankshaft, which transforms it into a rotary motion, which usually drives a gearbox through a clutch.


Ways of making power

There are two ways that a piston engine can make power. These are the two-stroke cycle and the four-stroke cycle. A two stroke engine produces power every stroke, while a four stroke engine produces power every other stroke. Older designs of small two-stroke engines produced more pollution than four stroke engines, however modern two-stroke designs, like the Vespa ET2 Injection utilise fuel-injection and are as clean as four-strokes. Large diesel two-stroke engines, as used in ships and locomotives, have always used fuel injection and produce low emissions. One of the biggest internal combustion engines in the world, the Wärtsilä-Sulzer RTA96-C is a two-stroke; it is bigger than most two-storey houses, has pistons nearly 1 metre in diameter and is one of the most efficient mobile engines in existence. In theory, a four stroke engine has to be larger than a two stroke engine to produce an equivalent amount of power. Two stroke engines are becoming less common in developed countries these days, mainly due to manufacturer reluctance to invest in reducing two-stroke emissions. Traditionally, two stroke engines needed more maintenance, even though they have less moving parts and tended to wear out faster than four stroke engines, however fuel-injected two-strokes achieve better engine lubrication and cooling and reliability should improve considerably.


External combustion engine

A steam engine is another type of piston engine. In most steam engines, the pistons are double acting: steam is alternately admitted to either end of the cylinder, so that every piston stroke produces power. .

Single cylinder engines

A single cylinder engine, colloquially known as a one-lunger, is an engine configuration consisting of just one cylinder, the simplest arrangement possible for an Otto or Diesel engine. The mounting can be standing, lying or angled.


Pros and Cons

Compared to multi-cylinder engines, single cylinder engines have several advantages, primarily their simple and economical construction. Balance shafts and counterweights on the crankshaft must be used to balance the weight of reciprocating parts, and can be expensive and complicated due to the collective mass of multiple cylinders. Components such as the crank have to be just as strong as in a four-cylinder engine of the same capacity per cylinder, meaning that some parts are effectively four times heavier than they need to be for the total displacement of the engine. This leads to the biggest downside of the single cylinder engine: it develops considerably lower power to weight ratios than a multi-cylinder of the same type.


Uses

Some early automobiles, such as the Cadillac 1906 Model K and 1907 Models L and M used single-cylinder engines. Single cylinder engines were also popular at one time for marine uses. Today the most common configuration is the 50cc-two-stroke Otto seen in so many bikes and scooters. These vehicles allowed the first mass-motorisation in many countries. Most engines used in small portable appliances, such as chainsaws, generators and domestic lawn mowers, usually have one cylinder. Also, the one-lunger is used in working vehicles, motorsports, airplanes, and as an industrial motor.