The firing order is the sequence of power delivery of each cylinder in a multi-cylinder reciprocating engine.
This is achieved by sparking of the spark plugs in a gasoline engine in the correct order, or by the sequence of fuel injection in a Diesel engine. When designing an engine, choosing an appropriate firing order is critical to minimizing vibration, to improve engine balance and achieving smooth running, for long engine fatigue life and user comfort, and heavily influences crankshaft design.
In a gasoline engine, the correct firing order is obtained by the correct placement of the spark plug wires on the distributor. In a modern engine with an engine management system and direct ignition, the Engine Control Unit (ECU) takes care of the correct firing sequence. Especially on cars with distributors, the firing order is usually cast on the engine somewhere, most often on then m. Gcylinder head, the intake manifold or the valve cover(s).
Various firing orders for different engine layouts
|number of cylinders||firing order||example|
|Saab two-stroke, Perodua Kancil engine
BMW K75 engine, Subaru Justy engine
|Most straight-4s, Ford Taunus V4 engine
Some British Ford and Riley engines, Ford Kent engine, Riley Nine
Subaru 4-cylinder engines, Yamaha R1 crossplane
Volkswagen air-cooled engine
|Straight-five engine, Volvo 850, Audi 100
GM Atlas engine
|Mercedes-Benz M104 engine, Straight-6, Volkswagen VR6 engine, Opel Omega A, Nissan L Engine
Mercedes-Benz M272 engine, Volkswagen V6's (both engines are 90-degree V6's)
|7||1-3-5-7-2-4-6||7-cylinder single row radial engine|
|Nissan VK engine|
|Dodge Viper V10
BMW S85, Ford V10
|2001 Ferrari 456M GT V12
1997 Lamborghini Diablo VT
Caterpillar Inc. 3412E
Audi VW Bentley W12 engine
|14||1L-1R-2L-2R-4L-4R-6L-6R-7L-7R-5L-5R-3L-3R||(Wärtsilä)-Sulzer 14ZV40/48 V14 marine diesel|
|16||1-12-8-11-7-14-5-16-4-15-3-10-6-9-2-13||2003 Cadillac V16 engine|
Although the vast majority of automobile engines rotate clockwise as viewed from the front, some engines are designed by the manufacturer to rotate counter-clockwise to accommodate certain mechanical configurations. In these applications, the firing order is shown in a reverse order (though it still starts with 1). For the most common inline configurations, this gives firing orders of 1-3-2, 1-2-4-3, and 1-4-2-6-3-5. In addition to the reconfiguration of the plug wires or injector tubes, the valve timing must be accordingly modified.
Cylinder numbering and firing order
Notes on left/right and front/rear
When referring to cars, the left-hand side of the car is the side that corresponds with the driver's left, as seen from the driver's seat. It can also be thought of as the side that would be on the left if one was standing directly behind the car looking at it.
When referring to engines, the front of the engine is the part where the pulleys for the accessories (such as the alternator and water pump) are, and the rear of the engine is where the flywheel is, through which the engine connects to the transmission. The front of the engine may point towards the front, side or rear of the car.
In most rear-wheel drive cars, the engine is longitudinally mounted and the front of the engine also points to the front of the car. In front-wheel drive cars with a transverse engine, the front of the engine usually points towards the right-hand side of the car. One notable exception is Honda, where many models have the front of the engine at the left-hand side of the car.
In front-wheel-drive cars with longitudinally mounted engines, most often the front of the engine will point towards the front of the car, but some manufacturers (Saab, Citroën, Renault) have at times placed the engine 'backwards', with #1 towards the firewall. One notable car with this layout is the Citroën Traction Avant. This layout is uncommon today.
Cylinder numbering and firing orders for various engine layouts
In a radial engine the cylinders are numbered around the circle, with the #1 cylinder at the top. There are always an odd number of cylinders in each bank, as this allows for a constant alternate cylinder firing order: for example, with a single bank of 7 cylinders, the order would be 1-3-5-7-2-4-6. Moreover, unless there is an odd number of cylinders, the ring cam around the nose of the engine would be unable to provide the inlet valve open - exhaust valve open sequence required by the four-stroke cycle.
In a V engine, cylinder numbering varies among manufacturers. Generally speaking, the most forward cylinder is numbered 1, but some manufacturers will then continue numbering along that bank first (so that side of the engine would be 1-2-3-4, and the opposite bank would be 5-6-7-8) while others will number the cylinders from front to back along the crankshaft, so one bank would be 1-3-5-7 and the other bank would be 2-4-6-8. (In this example, a V8 is assumed). To further complicate matters, manufacturers may not have used the same system for all of their engines. It is important to check the numbering system used before comparing firing orders, because the order will vary significantly with crankshaft design (see crossplane).
As an example, the Chevrolet Small-Block engine has cylinders 1-3-5-7 on the left hand side of the car, and 2-4-6-8 on the other side, and uses a firing order of 1-8-4-3-6-5-7-2. Note that the order alternates irregularly between the left and right banks; this is what causes the 'burbling' sound of this type of engine.
This means that Chevy Generation 1 Small Block V8 engines and Ford 302 V8s (5.8L, 5.0L, 7.5L) have an identical firing pattern despite having a different firing order.
Likewise, the firing pattern is the same for Chevrolet & Chrysler V8 engines with a firing order of 1-8-4-3-6-5-7-2, and for Ford's V8 engines with a firing order of 1-5-4-2-6-3-7-8.
An exception is the Ford Flathead V8 where the number 1 cylinder is on the right front of the engine (same as other Ford V8's) but this cylinder is not the front cylinder of the engine. In this case number 5 is the front cylinder. A similar situation exists with the Pontiac V8's 455 etc. where the cylinders are numbered like a Chevrolet V8 but the right side bank is in front(like a Ford), this puts cylinder number 2 in front of number 1.
|V8 Cylinder bank||Ferrari||Audi||Ford
||GM & Chrysler||GM (Northstar)||GM (Holden)|
|Right side of vehicle||4321||1234||1234||2468||1357||1357|
|Left side of vehicle||5678||5678||5678||1357||2468||2468|
Even and uneven firing order
Evenly spaced firing order (also called even firing order or even firing interval) means that the angle between each firing is equal. In four-stroke engines this requires a firing interval of 720° divided by the number of cylinders. On the other hand, engines with unevenly spaced firing order (sometimes called odd firing order) not all angles between firings are equal, for example a six-cylinder engine with unevenly spaced firing order can have a combination of 90° and 150° firing intervals compared to a six-cylinder engine with even firing order which must have 720° / 6 = 120° firing interval.
Engines that are even-firing will sound more smooth and steady, while engines that are odd, or uneven firing will have a burble or a throaty, growling sound in the engine note, and, depending on the crankshaft design, will often have more vibrations due to the unevenness of power delivery. Most racing engines such as those in Formula One often have even firing intervals in all or the most part (e.g. within each bank of a V-engine) of their firing order, mostly for easier packaging of performance exhaust systems. Engines that employ some variation on the Big-bang firing order theme will often have an uneven firing order, because the original point was to roughen up the power delivery to affect traction behaviour.
Examples of odd-firing engines are Harley-Davidson Evolution engines and most 4-stroke V-Twins, 2009–2014 Yamaha YZF-R1, Audi V10 FSI as used in the Audi R8 V10 and 2nd / 3rd generation Lamborghini Gallardo, Viper V10, Yamaha V-Max and VMAX, Buick 231 Odd-Fire V6.
Examples of even-firing engines are Honda NSR500V and most 2-stroke V-Twins, most current production inline 4s (with the exception of the Yamaha R1), most current production V6s, Lotus Esprit V8, Porsche 918 Spyder, McLaren M838T engine, Audi V10, 1st generation Lamborghini Gallardo and Toyota LR engine.
Contrary to most car engines, a ship's engine or a power plant engine is numbered from the flywheel end towards the free end.
In ship and power plant V-type engines the numbering is A1... and B1... where the A-bank is on the left hand side and the B-bank is on the right hand side, looking from the flywheel end.
1997 Dakota firing order diagram
- Firing Orders, Cylinder Numbering and Distributor Rotation for American V8 engines
- V8 Engines, an analysis of firing orders and cylinder numbering of V8 engines.
- Firing order of cylinders