Stroke ratio, bore/stroke ratio and stroke/bore ratio are terms that are used to describe the form of a piston engine's cylinder when the piston is at the bottom dead center (bdc) point. A reciprocating engine, also often known as a piston engine, is a Heat engine that uses one or more reciprocating Pistons to convert A cylinder is the central working part of a Reciprocating engine, the space in which a Piston travels A piston is a component of Reciprocating engines Pumps and Gas compressors It is located in a cylinder and is made gas-tight by Piston The stroke ratio also gives a general direction of the engines characteristics. The bore is the diameter of the cylinder and the stroke is the length that piston travels, which is generated when pistons top dead center (tdc) and bottom dead center positions are compared, which is twice the crank throw. Geometry, a diameter of a Circle is any straight Line segment that passes through the center of the circle and whose Endpoints are on the There are two different types of stroke ratios that are often mixed together causing confusion: Bore/stroke ratio and Stroke/bore ratio
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Bore/stroke ratio
Bore/stroke is the most commonly used term, which is mainly used in the USA, Great Britain, Australia and some other countries.
An engine that has wider bore vs. stroke has a bore/stroke value of over 1.
For example an engine which has 100 mm (millimeter) bore and 80 mm stroke has a bore/stroke value of:
100 mm / 80 mm = 1. The Millimetre ( American spelling: millimeter, symbol mm) is a unit of Length in the Metric system, equal to 25
Such an engine is referred as oversquare or short-stroke engine.
An engine that has shorter bore vs. stroke has a bore/stroke value of under 1.
For example an engine which has 90 mm bore and 120 mm stroke has a bore/stroke value of:
90 mm / 120 mm = 0. 75
This type of engine is called an undersquare or long-stroke engine.
An engine that has equal bore and stroke has a bore/stroke value of 1.
For example an engine which has both 95 mm bore and stroke has a bore/stroke value of:
95 mm / 95 mm = 1. 00
This type of engine is called a square engine. Usually engines that have a bore/stroke ratio of 0. 95 to 1. 04 are referred as square engines.
Stroke/bore ratio
Stroke/bore ratio is generally more rare than bore/stroke ratio but is used in some countries, like in Finland for example. Stroke/bore ratio is similar to the bore/stroke ratio with the following exception:
When stroke/bore value is over 1 the engine is longstroke or undersquare and when the stroke/bore value is under 1 the engine is shortstroke or oversquare. However the square engine has a value of 1 in both cases.
For example an engine with 110 mm stroke and 80 mm bore, stroke/bore value 1. 375, is an undersquare or longstroke and an engine that has 70 mm stroke and 100 mm bore, stroke/bore value 0. 7, is oversquare or shortstroke.
Oversquare
A piston engine is oversquare or shortstroke if its cylinders have a greater bore (width, diameter) than stroke (length of piston travel). A reciprocating engine, also often known as a piston engine, is a Heat engine that uses one or more reciprocating Pistons to convert A cylinder is the central working part of a Reciprocating engine, the space in which a Piston travels This is generally considered to be a positive trait, since a shorter stroke means less friction and less stress on the crankshaft. The crankshaft, sometimes casually abbreviated to crank, is the part of an Engine which translates reciprocating Linear An oversquare engine is generally more reliable, wears less, and can be run at a higher speed; though with the aid of modern technology, the disadvantages of undersquare or longstroke engines have been overcome. Stroke ratio, bore/stroke ratio and stroke/bore ratio are terms that are used to describe the form of a piston engine's cylinder when the Stroke ratio, bore/stroke ratio and stroke/bore ratio are terms that are used to describe the form of a piston engine's cylinder when the In oversquare engines power does not suffer, but low-speed torque does to some degree, since torque is relative to crank throw (distance from the crank center to the piston pin center)—the leverage, essentially. In Physics, power (symbol P) is the rate at which work is performed or energy is transmitted or the amount of energy required or expended for A torque (τ in Physics, also called a moment (of force is a pseudo- vector that measures the tendency of a force to rotate an object about An oversquare engine cannot have as high a compression ratio as a similar engine with a lower bore/stroke ratio, and using the same octane fuel. This causes the oversquare engine to have poorer fuel economy, and somewhat poorer exhaust emissions. Engines can be modified by being "de-stroked", shortening the stroke to increase maximum rpms and top-end horsepower, at the expense of low-end torque.
Oversquare or shortstroke engines have a tendency to overheat, but modern designs usually compensate for this tendency. Oversquare engines are lighter and shorter than similar undersquare engines along the direction of piston travel, but they are wider in directions perpendicular to piston travel. As the length is not a large problem, these engine types are highly favored by many manufacturers because of their power and compact size.
Formula One engines have a bore to stroke ratio of approximately 2. 5:1 and are capable of revving to 19,000 rpm.
Undersquare
A piston engine is undersquare or longstroke if its cylinders have a smaller bore (width, diameter) than stroke (length of piston travel). A reciprocating engine, also often known as a piston engine, is a Heat engine that uses one or more reciprocating Pistons to convert A cylinder is the central working part of a Reciprocating engine, the space in which a Piston travels This can be a negative trait, since a longer stroke usually means greater friction, more stress on the crankshaft, and a smaller bore means smaller valves which restricts gaseous exchange; however, with the aid of modern technology, these are not the large problems that they used to be. The crankshaft, sometimes casually abbreviated to crank, is the part of an Engine which translates reciprocating Linear An undersquare engine usually has a lower redline than an oversquare one, but it may generate more low-end torque. This article discusses the term "redline" as it applies to internal combustion engine technology Stroke ratio, bore/stroke ratio and stroke/bore ratio are terms that are used to describe the form of a piston engine's cylinder when the A torque (τ in Physics, also called a moment (of force is a pseudo- vector that measures the tendency of a force to rotate an object about In addition, a longstroke or undersquare engine can have a higher compression ratio with the same octane fuel compared to a similar displacement engine with a higher bore/stroke ratio. The compression ratio is a single number that can be used to predict the performance of any engine particularly piston engines (but can be used on essentially any Internal-combustion Octane is a straight-chain Alkane with the Chemical formula CH3(CH26CH3 This also equals better fuel economy and somewhat better emissions. An undersquare engine does not overheat as easily as similar oversquare engine. Engines can be modified with a "stroker" crankshaft, which increases an engines stroke from stock, increasing torque.
Undersquare engines typically are, proportionally, shorter in length, heavier, and taller than equivalent oversquare ones, which is one of the reasons why this type of engine is not generally used.
Many British automobile companies used undersquare designs through the 1950s, largely because of a motor tax system that taxed cars by their cylinder bore. The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located Therefore, many of the most famous cars of that era use this design. This includes the Austin A-Series engine and many Nissan derivatives. Austin Motor Company 's small Straight-4 Automobile engine the A-Series, is one of the most common in the world
The Chrysler Slant-6, in the most common 225 cubic inch (3. Chrysler LLC is an American Automobile manufacturer that has been producing Automobiles since 1925 The Slant-6, known within Chrysler as the G-engine, is one of Chrysler 's two best known Automobile Engines along with the Hemi 7 L) version, is a massively undersquare engine with a 3. 40" (86 mm) bore and a 4. 125" (105 mm) stroke, producing most of its power right on the peak of its torque curve. A torque (τ in Physics, also called a moment (of force is a pseudo- vector that measures the tendency of a force to rotate an object about The achilles heel of this engine, otherwise known for its exceptional durability, is being over-revved by inexperienced drivers. This article deals with the phrase For other uses see Achilles Heel. Red line for a factory engine is under 4,500 rpm; red line with aftermarket connecting rods is about 5,500 rpm. In a reciprocating Piston engine, the connecting rod or conrod connects the Piston to the crank or Crankshaft. On the other hand, a well-maintained Slant-6 can be made to idle as low as 75 rpm (though this is *not* a recommended speed, neither the alternator nor the oil pump will function adequately). alternator is an electromechanical device that converts mechanical energy to Alternating current electrical energy In some circles, the Slant-6 is nicknamed "The Stump-Puller" for its diesel-like low-speed torque. A diesel engine is an Internal combustion engine which operates using the Diesel cycle (named after Dr Appropriate gearing and driving skill is required for performance use.
Willys also used mostly undersquare engines, in fact the L134 and F134 engines, with their fairly small 3. Willys was the brand name used by the United States Automobile company Willys-Overland Motors best known for its production of military and civilian The Willys L134 (nicknamed Go Devil) was a Straight-4 automobile engine made famous in the Jeep produced in World War II. The Willys F4-134 Hurricane was an Inline-4 Piston engine and powered the famous Jeep CJ in the CJ-3B CJ-5 and CJ-6 models 125 inch (79. 4 mm) bore and 4. 375 inch (111. 1 mm) stroke, are probably the most undersquare engines ever built.
Nowadays, undersquare engines tend to be quite rare, but this form of engine is still used in some applications. For example, a modern 8. 4 liter Valmet 645 inline-6 tractor diesel engine is a longstroke/undersquare engine, but has an output of over 300 horsepower (224 kW) with turbocharger and intercooler. The straight-6 or inline-6 engine (often abbreviated I6 or L6) is a six cylinder Internal combustion engine with all six cylinders A diesel engine is an Internal combustion engine which operates using the Diesel cycle (named after Dr Output is the term denoting either an exit or changes which exit a System and which activate/modify a Process. A turbocharger, or turbo, is an air Compressor used for forced-induction of an Internal combustion engine. An intercooler, or Charge air cooler, is an air-to-air or air-to-liquid heat exchange device used on turbocharged and supercharged (forced The popular Mazda Miata also uses an undersquare engine.
GM's infamous 2.5L I4 "Iron Duke" engine was used in many economy cars in the 80's including the Pontiac Fiero. General Motors Corporation ( GM) ( is a multinational automobile manufacturer founded in 1908 and headquartered in the United States. The Iron Duke (also called the 2500, 151, Pontiac 25, Cross Flow, and Tech IV, though the decal on the air filter assemblies The Pontiac Fiero is a mid-engined Sports car that was built by the Pontiac division of General Motors from 1984 to 1988 It is commonly believed that the engine is undersquare due to the low redline of 5000 rpm. However the bore is 4" and stroke is 3", making it a fairly oversquare engine. The redline is so low because the crankshafts were cast without piston counterweights and the connecting rods were poorly cast. The Fiero suffered engine fires in the 1984 model due to connecting rods snapping either due to overreving or suffering from oil starvation. Iron Dukes in the Fiero also caught fire because the height of the engine required a smaller oil pan to fit into the Fiero engine compartment. Low oil levels frequently led to overheating and engine fires. Even with a highly oversquare design, it is very important to point out that the bore ratio is not the determining factor in determining the maximum redline for an engine.
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