Straight-three engine

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Cylinder block of an inline three-cylinder engine

A straight-three engine,[1] also known as an inline-triple,[2][3][4][5] or inline-three[6][7] (abbreviated I3 or L3), is a reciprocating piston internal combustion engine with three cylinders arranged in a straight line or plane, side by side.


four stroke Straight-three engine with firing order 1-3-2

A crankshaft angle of 120 degrees is typically used by straight-three engines,[8] since this results in an evenly spaced firing interval. Another benefit of this configuration is perfect primary balance and secondary balance, however an end-to-end rocking couple is induced because there is no symmetry in the piston velocities about the middle piston. A balance shaft is sometimes used to reduce the vibrations caused by the rocking couple.

Other crankshaft angles have been used occasionally. The 1976-1981 Laverda Jota motorcycle used a 180 degree crankshaft, where the outer pistons rise and fall together and inner cylinder is offset from them by 180 degrees. This results in three power strokes evenly-spaced at 180 degrees each, and then no power strokes during the final 180 degrees of crankshaft rotation. The 2020 Triumph Tiger 900 motorcycle uses a "T-Plane" crankshaft where the crankshaft throws are at 90 intervals, such that the throws for cylinders 1 and 3 are separated by 180 degrees (therefore the three throws together forming a "T" shape when viewed from the end).[9][10]

Usage in cars[edit]

Circa-1960 Saab two-stroke engine
2010 Suzuki K10B engine

Amongst the first cars to use a straight-three engine is the 1953-1955 DKW F91, powered by a 900 cc (55 cu in) two-stroke engine. The 1956-1960 Saab 93 saw the introduced of Saab's 750 cc (46 cu in) two-stroke engine, which was also used in the Saab 95 and Saab 96 until 1980. The Wartburg cars (manufactured in East Germany) and FSO Syrena (manufactured in Poland) also used straight-three engines.

The 1967 Suzuki Fronte 360 uses a 256 cc (16 cu in) two-stroke engine. In 1980, Suzuki began production of a 543 cc (33 cu in) four-stroke engine, which was introduced in the Alto and Fronte models.

The Subaru EF engine is a 4-stroke petrol engine which was introduced in 1984 and used in the Justy[6] and the Sumo (the export version of the Sambar).

The straight-three versions of the Ford EcoBoost engine - a turbocharged 1.0-litre petrol engine - was introduced in the 2012 Ford Focus.[11] It uses of an unbalanced flywheel to shift the inherent three-cylinder imbalance to the horizontal plane where it is more easily managed by engine mounts, and so remove the need to use balancer shafts.[12] In 2016, cylinder deactivation was added, claimed to be a world first for three-cylinder engines.[13]

Other car engines
Years Name Fuel Notes
1977-1993 Daihatsu C-series Petrol Used in the Diahatsu Charade and Diahatsu Mira/Cuore[14]
1983-2001 Suzuki G10 Petrol Debuted in the Suzuki Cultus/Swift[6][15]
1986-1995 VM Motori R392 Diesel Turbocharged, used in the Alfa Romeo 33
1987-present Mitsubishi 3G8 Petrol Debuted in the Mitsubishi Minica
1991-2008 Daewoo S-TEC Petrol Used in the Daewoo Tico and Daewoo Matiz
1996-2002 GM X10XE Petrol Debuted in the Opel Corsa
1998-2007 Mercedes-Benz M160 Petrol Turbocharged, used by Smart
1998-2005 Volkswagen R3 PD TDI 3L Diesel Turbocharged, used in the Volkswagen Lupo and Audi A2[16]
1999-2014 Mercedes-Benz OM660 Diesel Turbocharged, used by Smart
1999-2005 VN Motori R 315 Diesel Turbocharged, debuted in the Hyundai Accent
2000-2006 Honda ECA1 Petrol Used by the Honda Insight hybrid car
2003-present Mitsubishi 3A9 Petrol Debuted in the Mitsubishi Mirage[17]
2004-2011 Hyundai U engine Diesel Turbocharged, debuted in the Kia Picanto
2004-present Volkswagen R3 (EA111) Petrol Debuted in the Volkswagen Fox[18]
2004-2009 Mercedes-Benz OM639 Diesel Turbocharged, used by the Smart Forfour and Mitsubishi Colt[19][20]
2004-present Toyota 1KR-FE Petrol Debuted in the Toyota Aygo
2010-present Nissan HR Petrol Some versions supercharged, debuted in the Nissan Micra[21]
2011-2017 Fiat XSDE Diesel Debuted in the India-market Chevrolet Beat[22]
2012-present BMW B37 Diesel Turbocharged, debuted in the Mini (F56)
2012-present Renault TCe Petrol Turbocharged, debuted in the Renault Clio IV
2013-present BMW B38 Petrol Turbocharged, debuted in the BMW i8
2013-present GM small gasoline engine Petrol Turbocharged, debuted in the Opel Adam[23][24]
2014-present PSA Group PureTech Petrol Turbocharged, debuted in the Peugeot 308

Motorcycle use[edit]

Closeup picture of a motorcycle engine with three heavily chromed exhaust pipes coming out of the side
Triumph Rocket III has a 2.3 L straight-three engine

For motorcycles, the inline three-cylinder engine is considered advantageous as it is narrower than an inline-four and produces less vibration than a twin cylinder vehicle.[25]


Four-stroke straight-three motorcycle engines have been produced for both road and racing purposes[26] by Aprilia, Laverda,[26][27] Triumph, Yamaha, BMW, Benelli, Petronas, MV Agusta, and BSA.[26][28]

When BMW first moved to watercooled engines they first released the K100 I4 closely followed by the K75 with a 3 in line engine. the K75 was very popular due to the lower weight and the good torque range provided by the 3 cylinder engine.

The Triumph Rocket III, has a 2,294 cc (140.0 cu in) straight-three engine and the company has produced a number of other transversely mounted straight-three engines,[29] such as the water-cooled T509 Speed Triple, which was also the company's first fuel injected machine; and 1,050 cc Speed Triple.[30]

In 2019, the Moto2 class in the MotoGP World Championship switched to using Triumph 765 cc (46.7 cu in) triple engines.[31]

Current production motorcycles with triple engines:


Kawasaki H1 Mach III

Following a comparative study at Osaka University's Faculty of Engineering, between in-line and L-shaped motors, Kawasaki Motors decided to develop a range of high performance, two stroke straight-three engines.[32] Between 1969 and 1978, the company produced air-cooled inline, triple engines with capacities of 250 cc, 350 cc, 400 cc, 500 cc, and 750 cc,[33] and the H1-R 500cc and H2-R or KR750 750 cc racing models in both air-cooled and water-cooled forms.[34]

Between 1972 and 1977, Suzuki made three two-stroke straight-three production runs; the air-cooled GT380 and GT550, and the water-cooled GT750 and TR750 racer based on it.[34]

Non-automotive use[edit]

Fairbanks-Morse inline three diesel engine and pump

Inline three-cylinder engines are not limited to propelling motor vehicles. They may also be used in general industrial applications. An example is the Fairbanks-Morse 32E14 slow-speed diesel engine which is shown coupled to a water pump.

Agricultural use[edit]

Inline three engines are common in diesel engined tractors, as well as other agricultural machinery. Nearly all manufacturers of diesel tractors have had models with three-cylinder engines. Perhaps the best known example of any kind of three-cylinder diesel engine is the Perkins AD3.152 that was used in Massey Ferguson 35 tractors, as well as in Fordson Dexta and several other tractors. This engine was also used for marine and stationary applications. Other manufacturers include Nuffield (BMC), Bolinder-Munktell/Volvo BM, International Harvester, John Deere, Deutz-Fahr, Kubota, Ford and many others.

Aviation use[edit]

The Hewland AE75 is a 750 cc lightweight two-stroke inverted three-cylinder liquid-cooled aircraft engine that produced 75 bhp (56 kW), manufactured in the mid-1980s by Hewland.[35]

See also[edit]


  1. ^ Robson, Graham (August 15, 2010). "The car and the team". Saab 96 & V4. Rally Giants. Veloce Publishing. p. 27. ISBN 978-1-84584-256-7. V4 replaces straight three
  2. ^ Let's Ride: Sonny Barger's Guide to Motorcycling. Sonny Barger, Darwin Holmstrom. HarperCollins, 8 Jun 2010
  3. ^ Superbikes: The World's Top Performance Machines. Alan Dowds. Tangerine Press, 2004
  4. ^ Cycle world, Volume 44. CBS Publications, 2005
  5. ^ Gorant, Jim (December 1997). Oldham, Joe (ed.). "Jet Ski Saviors". Popular Mechanics. New York, NY USA: Hearst. 174 (12): 54–57. ISSN 0032-4558. Retrieved 2012-07-02. The 1071cc, inline, triple-cylinder configuration produces 803 pounds of thrust and pushes the boat to about 55 mph.
  6. ^ a b c Dinkel, John, ed. (July 1988). "Comparison Road Test: 3x3". Road & Track. Newport Beach, CA USA: Diamandis Communications. 39 (11): 66–74. ISSN 0035-7189. Its engine is still the same 993-cc sohc inline-3, producing 48 bhp at 5100 5100 rpm and 57 lb-ft torque at 3200...
  7. ^ Mayersohn, Norman; Zino, Ken (March 1988). Oldham, Joe (ed.). "Car of the Future Part 3 of a Series – Power for Tomorrow". Popular Mechanics. New York, NY USA: Hearst. 165 (3): 53–57. ISSN 0032-4558. Retrieved 2012-07-02. Under a more sophisticated modular engine plan, a basic 3-liter V6 could be split into an inline Three, chopped into a V4 or melded into a V12.
  8. ^ "Here's The Problem With Three-Cylinder Engines". Car Throttle. Retrieved 2019-12-03.
  9. ^ "TIGER 900 ENGINE & CAPABILITY". Triumph Motorcycles UK. Retrieved 10 February 2020.
  10. ^ Cameron, Kevin. "Triumph's New T-Plane Firing Order Explained". Cycleworld. Retrieved 10 February 2020.
  11. ^ "Smallest Ford Engine Ever! Three-Cylinder EcoBoost (and Two New Transmissions)". Retrieved 2017-04-03.
  12. ^ "Ford's 3-cyl. EcoBoost Delivers the Goods". 2014-05-15. Retrieved 2017-04-03.
  13. ^ "Ford To Offer Fuel-Saving Cylinder Deactivation Tech FOR 1.0 Litre EcoBoost; Global First For A 3-Cylinder Engine". 2016-11-29. Retrieved 2017-04-03.
  14. ^ Logan (September 23, 2011). "New car: 2012 Daihatsu Mira e:S". Motor Mania. Retrieved 2012-07-03. Motivation comes from a 3-cylinder, 650cc petrol engine that kicks out a mere 51bhp (52PS/38kW) and 60Nm (44lb-ft) of torque.
  15. ^ Daniel Zevedei. "Suzuki Swift 1.0 GL - 5-doors, hatchback". Retrieved 2014-06-20.
  16. ^ "Audi A2 1.2 TDI: the three-litre car from Audi". AUDI AG - press release. 1999-11-28. Retrieved 2009-08-22.
  17. ^ Jackson, Paul (February 1, 2008). "Chapter 6: The Next Generation". The Little Book of Smart. Veloce Publishing. pp. 94–95. ISBN 978-1-84584-148-5. There were plenty of changes under the skin, too, with the original smart-built turbocharged engine being replaced (on petrol-engined versions) by a Mitsubishi design – still with three cylinders but now a larger (999cc) capacity.
  18. ^ "New VW Fox in depth". Volkswagen AG. 2005-04-04. Retrieved 2009-08-18.
  19. ^ Daniel Zevedei. "Mitsubishi Colt 1.1 Inform - 5-doors, hatchback". Retrieved 2014-06-20.
  20. ^ "Om639 Engine - Diesel Engine - Turbocharger". Scribd. Retrieved 2020-08-24.
  21. ^ "HR12DDR Engine | NISSAN | TECHNOLOGICAL DEVELOPMENT ACTIVITIES". Retrieved 2014-06-20.
  22. ^ "LAUNCHED! Chevrolet Beat diesel starts at Rs 4.29 lakh". BS Motoring. July 25, 2011.
  23. ^ "New All-Aluminum 3-Cylinder Turbo Sets Refinement Benchmark". 2013-08-07. Retrieved 2014-06-20.
  24. ^ "Opel presents new 1.0 ECOTEC Direct Injection Turbo engine at Aachen Colloquium". 2013-10-08. Retrieved 2014-06-20.
  25. ^ How Your Motorcycle Works: Your Guide to the Components & Systems of Modern Motorcycles. Peter Henshaw Veloce Publishing Ltd, 15 Sep 2012
  26. ^ a b c 365 Motorcycles You Must Ride. Dain Gingerelli, Charles Everitt, James Manning Michels. MBI Publishing Company, 10 Jan 2011
  27. ^ The Motorcycle Book, Alan Seeley. MotorBooks International, 2 May 2004
  28. ^ Human Hurricane, Wilson, Steve. Walneck's Classic Cycle Trader, April 2005
  29. ^ Triumph Motorcycles: Twins & Triples. Timothy Remus. MotorBooks International, 10 Oct 1997
  30. ^ Cycle world, Volume 44 CBS Publications, 2005. "inline triple"
  31. ^ Triumph enters Grand Prix racing as Moto2 engine supplier The Telegraph, 18 December 2018. Retrieved 15 December 2019.
  32. ^ The Kawasaki Triples Bible: All Road Models 1968-1980, Plus H1r and H2r Racers in Profile. Alastair Walker, Veloce Publishing Ltd, 15 Jan 2011. P.18
  33. ^ 365 Motorcycles You Must Ride. Dain Gingerelli, Charles Everitt, James Manning Michels. MBI Publishing Company, 10 Jan 2011. P.188
  34. ^ a b Japanese Production Racing Motorcycles. Mick Walker. Redline Books, Sep 2004
  35. ^ “Pilot” magazine February 1986 page 32