Stroke ratio

Last updated

Bore/Stroke comparison Bore Stroke Ratio Animation.gif
Bore/Stroke comparison

Stroke ratio, today universally defined as bore/stroke ratio, is a term to describe the ratio between cylinder bore diameter and piston stroke length in a reciprocating piston engine. This can be used for either an internal combustion engine, where the fuel is burned within the cylinders of the engine, or external combustion engine, such as a steam engine, where the combustion of the fuel takes place outside the working cylinders of the engine.

Contents

Conventions

The contemporary convention for describing the stroke ratio of a piston engine‘s cylinders is its bore/stroke ratio. [1]

Stroke/bore ratio is an obsolete expression dating to the early era of reciprocating engine development. [2]

Bore/stroke ratio

The diameter of the cylinder bore is divided by the length of the piston stroke to give the ratio.

Square, oversquare and undersquare engines

The following terms describe the naming conventions for the configurations of the various bore/stroke ratio:

Square

A square engine has equal bore and stroke dimensions, giving a bore/stroke value of exactly 1:1.

Square engine examples

1953 – Ferrari 250 Europa had Lampredi V12 with 68.0 mm × 68.0 mm (2.7 in × 2.7 in) bore and stroke.

1967 – FIAT 125, 124Sport engine 125A000, 125B000, 125BC000, 1608 ccm, DOHC, 80.0 mm × 80.0 mm (3.15 in × 3.15 in) bore and stroke.

1970 – Ford 400 had a 101.6 mm × 101.6 mm (4.00 in × 4.00 in) bore and stroke.

1973 – Kawasaki Z1 and KZ(Z)900 had a 66.0 mm × 66.0 mm (2.60 in × 2.60 in) bore and stroke. [3]

1982 - Honda Nighthawk 250 and Honda CMX250C Rebel have a 53.0 mm × 53.0 mm (2.09 in × 2.09 in) bore and stroke. [4]

1983 – Mazda FE 2.0L inline four-cylinder engine with a 86.0 mm × 86.0 mm (3.4 in × 3.4 in) bore and stroke.

1987 – The Opel/Vauxhall 2.0 L GM Family II engines are square at 86.0 mm × 86.0 mm (3.39 in × 3.39 in) bore and stroke; example as C20XE C20NE C20LET X20A X20XEV X20XER Z20LET Z20LEH Z20LER A20NHT A20NFT.

1989 – Nissan's SR20DE is a square engine, with an 86.0 mm × 86.0 mm (3.39 in × 3.39 in) bore and stroke.

1990–2010 Saab B234/B235 is a square engine, with a 90.0 mm × 90.0 mm (3.54 in × 3.54 in) bore and stroke.

1991 – Ford's 4.6 V8 OHC engine has a 90.2 mm × 90.0 mm (3.552 in × 3.543 in) bore and stroke.

1995 – The BMW M52 engine with a displacement of 2793 cubic centimeters is an example of a perfect square engine with an 84.0 mm × 84.0 mm (3.31 in × 3.31 in) bore and stroke.

1996 – Jaguar's AJ-V8 engine in 4.0-litre form has an 86.0 mm bore and stroke.

2000 – Mercedes-Benz 4.0-litre (3996 cc; 243.9 cu in) OM628 V8 diesel engine is an example of a square engine – with an 86.0 mm × 86.0 mm (3.39 in × 3.39 in) bore and stroke.

Oversquare

An engine is described as oversquare or short-stroke if its cylinders have a greater bore diameter than its stroke length, giving a bore/stroke ratio greater than 1:1.

An oversquare engine allows for more and larger valves in the head of the cylinder, higher possible rpm by lowering maximum piston speed, and lower crank stress due to the lower peak piston acceleration for the same engine (rotational) speed. Because these characteristics favor higher engine speeds, oversquare engines are often tuned to develop peak torque at a relatively high speed.

Due to the increased piston and head surface area, the heat loss increases as the bore/stroke ratio is increased. Thus an excessively high ratio can lead to a decreased thermal efficiency compared to other engine geometries. The large size/width of the combustion chamber at ignition can cause increased inhomogeneity in the air/fuel mixture during combustion, resulting in higher emissions.

The reduced stroke length allows for a shorter cylinder and sometimes a shorter connecting rod, generally making oversquare engines less tall but wider than undersquare engines of similar engine displacement.

Oversquare engine examples

Oversquare engines (a.k.a. "short stroke engines") are very common, as they allow higher rpm (and thus more power), without excessive piston speed.

Examples include both Chevrolet and Ford small-block V8s; the GMC 478 V6 has a bore/stroke ratio of 1.33. The 1.6 litre version of the BMW N45 gasoline engine has a bore/stroke ratio of 1.167.

Horizontally opposed, also known as "Boxer" or "flat", engines typically feature oversquare designs since any increase in stroke length would result in twice the increase in overall engine width. This is particularly so in Subaru’s front-engine layout, where the steering angle of the front wheels is constrained by the width of the engine. The Subaru EJ181 engine develops peak torque at speeds as low as 3200 rpm.

Nissan's RB, VQ, VK, VH and VR38DETT engines are all oversquare. Additionally, SR16VE engine found in Nissan Pulsar VZ-R and VZ-R N1 is an oversquare engine with 86 millimetres (3.39 in) bore and 68.7 millimetres (2.70 in) stroke, giving it 175–200 horsepower (130–150 kW) but relatively small torque of 119–134 pound-feet (161–182 N⋅m; 16.5–18.5 kg⋅m)

Extreme oversquare engines are found in Formula One racing cars, where strict rules limit displacement, thereby necessitating that power be achieved through high engine speeds. Stroke ratios approaching 2.5:1 are allowed, [lower-alpha 1] enabling engine speeds of 18,000 rpm while remaining reliable for multiple races. [5]

The Ducati Panigale motorcycle engine is extremely oversquare with a bore/stroke ratio of 1.84:1. It was given the name "SuperQuadro" by Ducati, roughly translated as "super-square" from Italian. [6]

The side-valve Belgian D-Motor LF26 aero-engine has a bore/stroke ratio of 1.4:1. [7]

Early Mercedes-Benz M116 engines had a 92 millimetres (3.62 in) bore and a 65.6 millimetres (2.58 in) stroke for a 3.5 litre V8. [8]

Undersquare

An engine is described as undersquare or long-stroke if its cylinders have a smaller bore (width, diameter) than its stroke (length of piston travel) - giving a ratio value of less than 1:1.

At a given engine speed, a longer stroke increases engine friction and increases stress on the crankshaft due to the higher peak piston acceleration. The smaller bore also reduces the area available for valves in the cylinder head, requiring them to be smaller or fewer in number.

Undersquare engines often exhibit peak torque at lower rpm than an oversquare engine due to their smaller valves and high piston speed limiting their potential to rev higher.

Undersquare engines have become more common lately, as manufacturers push for more and more efficient engines and higher fuel economy.[ clarify ] [9]

Undersquare engine examples

Many inline engines, particularly those mounted transversely in front-wheel-drive cars, utilize an undersquare design. The smaller bore allows for a shorter engine that increases room available for the front wheels to steer. Examples of this include many Volkswagen, Nissan, Honda, and Mazda engines. The 1KR-FE-engine used in the Toyota Aygo, Citroën C1 and Peugeot 107 amongst others is an example of a modern long-stroke engine widely used in FF layout cars. This engine has a bore and stroke of 71 mm × 84 mm (2.8 in × 3.3 in) stroke giving it a bore/stroke ratio of 0.845:1. Some rear-wheel-drive cars that borrow engines from front-wheel-drive cars (such as the Mazda MX-5) use an undersquare design.

BMW's acclaimed S54B32 M54 engine was undersquare with a bore and stroke of 87 mm × 91 mm (3.4 in × 3.6 in)), offering a world record torque-per-litre figure (114 N⋅m/L, 1.38 lb⋅ft/cu in) for normally-aspirated production engines at the time; this record stood until Ferrari unveiled the 458 Italia.

Many British automobile companies used undersquare designs until the 1950s, largely because of a motor tax system that taxed cars by their cylinder bore. This includes the BMC A-Series engine, and many Nissan derivatives. The Trojan Car used an undersquare, split piston, two stroke, two-cylinder inline engine; this was partly for this tax advantage and partly because its proportions allowed flexing V-shaped connecting rods for the two pistons of each U-shaped cylinder, which was cheaper and simpler than two connecting rods joined with an additional bearing.

Their French and German competitors at the time also used undersquare designs even in absence of the tax reasoning, e. g. Renault Billancourt engine and Opel straight-6 engine.

The 225 cu in (3.7  litre) Chrysler Slant-6 engine is undersquare, with a bore and stroke of 86 mm × 105 mm (3.4 in × 4.1 in) stroke (bore/stroke ratio = 0.819:1).

The Ford 5.4L Modular Engine features a bore and stroke of 90.1 mm × 105.8 mm (3.55 in × 4.17 in), which makes a bore/stroke ratio of 0.852:1. Since the stroke is significantly longer than the bore, the SOHC 16V (2-valve per cylinder) version of this engine is able to generate a peak torque of 350 lb·ft as low as 2501 rpm.

The Willys Jeep L134 and F134 engines were undersquare, with a bore and stroke of 79.4 mm × 111.1 mm (3.13 in × 4.37 in) stroke (bore/stroke ratio = 0.714:1).

The Dodge Power Wagon used a straight-six Chrysler Flathead engine of 230 cu in (3.8 L) with a bore and stroke of 83 mm × 117 mm (3.3 in × 4.6 in), yielding a substantially undersquare bore/stroke ratio of 0.709:1.

The 4-litre Barra Inline 6 engine from the Australian Ford Falcon, uses a bore and stroke of 92.21 mm × 99.31 mm (3.63 in × 3.91 in) stroke, which equates to a 0.929:1 bore-stroke ratio.

The 292 Chevrolet I6 is also undersquare, with a bore and stroke of 98.4 mm × 104.8 mm (3.875 in × 4.125 in) in (bore/stroke ratio = 0.939:1).

Mitsubishi's 4G63T engine found primarily in many generations of Mitsubishi Lancer Evolution is an undersquare engine with a bore and stroke of 85 mm × 88 mm (3.3 in × 3.5 in).

The Jaguar XK6 engine, used in all 6-cylinder Jaguars from 1949 to 1987 was undersquare. For example, the 4.2 litre engine had a bore and stroke of 92.08 mm × 106 mm (3.63 in × 4.17 in), providing a bore/stroke ratio of 0.869:1.

Virtually all piston engines used in military aircraft were long-stroke engines. The PW R-2800, Wright R-3350, Pratt & Whitney R-4360 Wasp Major, Rolls-Royce Merlin (1650), Allison V-1710, and Hispano-Suiza 12Y-Z are only a few of more than a hundred examples.

All diesel-powered ships have massively undersquare marine engines, usually using crossheads. A Wärtsilä two-stroke marine diesel engine has a bore and stroke of 960 mm × 2,500 mm (37.8 in × 98.4 in), (bore/stroke ratio = 0.384:1).

While most modern motorcycle engines are square or oversquare, some are undersquare. The Kawasaki Z1300's straight-six engine was made undersquare to minimise engine width, more recently, a new straight-twin engine for the Honda NC700 series used an undersquare design to achieve better combustion efficiency in order to reduce fuel consumption. [10] [11]

Notes

  1. ↑ There is no actual restriction on bore:stroke ratio, but cylinder bores are limited to 98 millimetres or 3.86 inches and capacity to 2,400 cubic centimetres (150 cu in).

Related Research Articles

<span class="mw-page-title-main">Nissan VK engine</span> Reciprocating internal combustion engine

The VK engine is a V8 piston engine from Nissan. It is an aluminum DOHC 4-valve design.

<span class="mw-page-title-main">Nissan RB engine</span> Reciprocating internal combustion engine

The RB engine is an oversquare 2.0–3.0 L straight-6 four-stroke gasoline engine from Nissan, originally produced from 1985 to 2004. The RB followed the 1983 VG-series V6 engines to offer a full, modern range in both straight or V layouts. It was part of a new engine family name PLASMA.

<span class="mw-page-title-main">Nissan QG engine</span> Reciprocating internal combustion engine

The QG engine is a 1.3 L (1,295 cc), 1.5 L (1,497 cc), 1.6 L (1,597 cc) and 1.8 L (1,769 cc) straight-4 piston engine from Nissan. It is a lean-burn aluminum DOHC 4-valve design with variable valve timing and optional NEO Di direct injection.

<span class="mw-page-title-main">Nissan KA engine</span> Reciprocating internal combustion engine

The KA engines were a series of four-stroke inline-four gasoline piston engines manufactured by Nissan, which were offered in 2.0 and 2.4 L. The engines blocks were made of cast-iron, while the cylinder heads were made of aluminum.

<span class="mw-page-title-main">Mitsubishi Astron engine</span> Reciprocating internal combustion engine

The Mitsubishi Astron or 4G5/4D5 engine, is a series of straight-four internal combustion engines first built by Mitsubishi Motors in 1972. Engine displacement ranged from 1.8 to 2.6 litres, making it one of the largest four-cylinder engines of its time.

<span class="mw-page-title-main">Lamborghini V8</span> Reciprocating internal combustion engine

The Lamborghini V8 is a ninety degree (90°) V8 petrol engine designed by Lamborghini in the 1970s for their less-expensive vehicles. It was only the second internal combustion engine ever developed by the company, and first saw production for the 1971 Lamborghini Urraco. It was designed by Giampaolo Dallara. The all-aluminium alloy engine was introduced as a 2.5-litre variant, displacing 2,463 cc (150.3 cu in), but was expanded, by increasing the piston stroke to a 3.0-litre variant for 1975 - now displacing 2,997 cc (182.9 cu in).

<span class="mw-page-title-main">Toyota JZ engine</span> Reciprocating internal combustion engine

The Toyota JZ engine family is a series of inline-6 automobile engines produced by Toyota Motor Corporation. As a replacement for the M-series inline-6 engines, the JZ engines were 24-valve DOHC engines in 2.5- and 3.0-litre versions.

The Honda B20A engine series, known as the B20A and B21A, was an inline four-cylinder engine family from Honda introduced in 1985 in the second-generation Honda Prelude. Also available in the contemporary third-generation Honda Accord in the Japanese domestic market, along with the Accord-derived Vigor, the B20A was Honda's second line of multivalve DOHC inline four-cylinder engines behind the "ZC" twin-cam variant of the ordinarily SOHC D-series, focused towards performance and displacing 2.0 to 2.1 litres.

<span class="mw-page-title-main">BMC A-series engine</span> Reciprocating internal combustion engine

The Austin Motor Company A-series is a British small straight-4 automobile engine. Launched in 1951 with the Austin A30, production lasted until 2000 in the Mini. It used a cast-iron block and cylinder head, and a steel crankshaft with three main bearings. The camshaft ran in the cylinder block, driven by a single-row chain for most applications, and with tappets sliding in the block, accessible through pressed steel side covers for most applications, and with overhead valves operated through rockers. The cylinder blocks are not interchangeable between versions intended for conventional end-on mounted gearboxes and the 'in-sump' transaxle used on British Motor Corporation/British Leyland front wheel drive models such as the Mini. The cylinder head for the overhead-valve version of the A-series engine was designed by Harry Weslake – a cylinder head specialist famed for his involvement in SS (Jaguar) engines and several Formula One-title winning engines. Although a "clean sheet" design, the A-series owed much to established Austin engine design practise, resembling in general design and overall appearance a scaled-down version of the 1200cc overhead-valve engine first seen in the Austin A40 Devon which would form the basis of the later B-series engine.

<span class="mw-page-title-main">Nissan L engine</span> Reciprocating internal combustion engine

The Nissan L series of automobile engines was produced from 1966 through 1986 in both inline-four and inline-six configurations ranging from 1.3 L to 2.8 L. It is a two-valves per cylinder SOHC non-crossflow engine, with an iron block and an aluminium head. It was most notable as the engine of the Datsun 510, Datsun 240Z sports car, and the Nissan Maxima. These engines are known for their reliability, durability, and parts interchangeability.

<span class="mw-page-title-main">Honda D engine</span> Japanese automobile engines

The Honda D series inline-four cylinder engine is used in a variety of compact models, most commonly the Honda Civic, CRX, Logo, Stream, and first-generation Integra. Engine displacement ranges between 1.2 and 1.7 liters. The D Series engine is either SOHC or DOHC, and might include VTEC variable valve lift. Power ranges from 66 PS (49 kW) in the Logo to 130 PS (96 kW) in the Civic Si. D-series production commenced in 1984 and ended in 2005. D-series engine technology culminated with production of the D15B 3-stage VTEC (D15Z7) which was available in markets outside of the United States. Earlier versions of this engine also used a single port fuel injection system Honda called PGM-CARB, signifying the carburetor was computer controlled.

<span class="mw-page-title-main">Honda F engine</span> Reciprocating internal combustion engine

The Honda F-Series engine was considered Honda's "big block" SOHC inline four, though lower production DOHC versions of the F-series were built. It features a solid iron or aluminum open deck cast iron sleeved block and aluminum/magnesium cylinder head.

<span class="mw-page-title-main">Mean piston speed</span> Average speed of the piston in a reciprocating engine

The mean piston speed is the average speed of the piston in a reciprocating engine. It is a function of stroke and RPM. There is a factor of 2 in the equation to account for one stroke to occur in 1/2 of a crank revolution and a '60' to convert seconds from minutes in the RPM term.

<span class="mw-page-title-main">Honda L engine</span> Inline-four engine

The L-series is a compact inline-four engine created by Honda, introduced in 2001 with the Honda Fit. It has 1.2 L (1,198 cc), 1.3 L (1,318 cc) and 1.5 litres (1,497 cc) displacement variants, which utilize the names L12A, L13A and L15A. Depending on the region, these engines are sold throughout the world in the 5-door Honda Brio Fit/Jazz hatchback Honda Civic and the 4-door Fit Aria/City sedan. They can also be found in the Japanese-only Airwave wagon and Mobilio MPV.

<span class="mw-page-title-main">Nissan MA engine</span> Reciprocating internal combustion engine

The MA is a straight-4 SOHC 0.9 L, 1.0 L, or 1.2 L engine first introduced in 1982 by Nissan, intended primarily for the K10 series Micra/March model. It shares design similarities with the older E engine, with an 8-valve hemispherical cylinder head but differs in that it uses an aluminium cylinder block. Unusually, the specified ignition timing for the MA10 running on the specified 90 RON gasoline was 2 degrees after top dead centre, reflecting a very high flame speed in the compact combustion chambers.

In a piston engine, the bore is the diameter of each cylinder.

<span class="mw-page-title-main">Nissan VRH engine</span> Reciprocating internal combustion engine

The Nissan VRH engine family consists of several racing engines built by Nissan Motor Company beginning in the late 1980s. All VRH engines are in a V8 configuration, with either natural aspiration or forced induction. Some VRH engines are loosely based on Nissan's production V8 engine blocks, including the VH and VK engines, while others were designed from the ground up for racing and share no components with production blocks.

References

  1. ↑ Bore/stroke is the more commonly used term, with usage in North America, Europe, United Kingdom, Asia, and Australia.[ citation needed ]
  2. ↑ Ingram, Edward (April 1916). "As to the Matter of Stroke". Horseless Age. 37 (6 & 7): 275, 325. Retrieved 12 November 2015.
  3. ↑ "Kawasaki 900 Super Four". 240 Landmarks of Japanese Automotive Technology. Society of Automotive Engineers of Japan, Inc. Retrieved 6 November 2013. Journalists and riders called it the king of motorcycles, and it gained a reputation as a super sport model all over the world. The Super Four boasted high performance and quality. This best-selling motorcycle won many prizes around the world within only six months of its release.
  4. ↑ "2013 Honda Rebel Specifications". Honda Media Newsroom. American Honda Motor Co. 4 September 2012. Retrieved 25 March 2014.
  5. ↑ "2011F1 Technical Regulations" (PDF). FIA. Retrieved 21 July 2011.
  6. ↑ "Ducati 1199 Panigale - Ducati". www.1199panigale.ducati.com. Retrieved 9 April 2018.
  7. ↑ "Price". Netherlands: D-Motor. Archived from the original on 25 April 2012.
  8. ↑ "Mercedes Benz 350SL Technical Specifications". Archived from the original on 31 August 2007.
  9. ↑ "2.0-liter Dynamic Force Engine, a New 2.0-liter Direct-injection, Inline 4-cylinder Gasoline Engine" (Press release). Japan: Toyota. 26 February 2018. Retrieved 11 June 2018.
  10. ↑ "Global 700cc Engine for Next-Generation : Technical details". Honda Worldwide. Honda Motor Co. 8 March 2012. p. 5. Retrieved 25 March 2014.
  11. ↑ Garrett, Jerry (14 September 2012). "Reality Check From Honda, in Touch With Economics". New York Times. Retrieved 25 March 2014.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.