Firing order
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The firing order is the sequence of sparking of the spark plugs in a reciprocating engine, or the sequence of fuel injection in each cylinder in a Diesel engine. Choosing an appropriate firing order is critical to minimizing vibration and achieving smooth running, for long engine fatigue life and user comfort.
In a straight engine the spark plugs (and cylinders) are numbered, starting with #1, from the front of the engine to the rear. In most cars the front of the engine also points to the front of the car, but some manufacturers (Saab, Citroën) in some models place the engine 'backwards', with #1 towards the firewall.
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 well-known 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 righthand 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 famous 'burbling' sound of this type of engine. [1]
In a radial engine the cylinders are numbered around the circle, with the #1 cylinder at the top. There are almost always an odd number of cylinders, as this allows for a constant every-other-piston firing order: for example, with a single bank of 7 cylinders, the order would be ...2-4-6-1-3-5-7-2....
The numbers are usually cast on the cylinder head or the intake manifold or the valve cover(s).
In a conventional 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 Electronic Control Unit (ECU) takes care of the correct firing sequence.
These are some usual firing orders:
| number of cylinders | firing order | example |
|---|---|---|
| 3 | 1-3-2 | Saab two-stroke engine |
| 4 | 1-3-4-2 | Ford Taunus V4 engine |
| 5 | 1-2-4-5-3 | Volvo 850 Audi 100 |
| 6 | 1-5-3-6-2-4 1-6-5-4-3-2 |
Jeep CJ 1949-1986 GM 3800 engine |
| 7 (radial) | 1-3-5-7-2-4-6 | |
| 8 | 1-8-4-3-6-5-7-2 1-8-7-2-6-5-4-3 |
1988 Chrysler Fifth Avenue, Small Block V8 LS1 |
| 10 | 1-10-9-4-3-6-5-8-7-2 | Dodge Viper |
| 12 | 1-7-5-11-3-9-6-12-2-8-4-10 | 2001 Ferrari 456M GT |
| 16 | 1-12-8-11-7-14-5-16-4-15-3-10-6-9-2-13 | Cadillac V16 engine |
[edit] Trivia
- The neon lights on Flo's V8 Cafe in the movie Cars flash in the proper firing order for a Ford flathead V8.
