The firing order of an internal combustion engine is the sequence of ignition for the cylinders. In a spark-ignition (e.g. gasoline/petrol) engine, the firing order corresponds to the order in which the spark plugs are operated. Firing order affects the vibration, sound, and evenness of power output from the engine.
In engines, cylinders don’t fire in the sequence of 1-2-3-4-5-6 and so on as it could cause the crankshaft to deform or break. The order or sequence in which the engine cylinders fire or generate & deliver power is called the engine firing order.
Related: What is an Internal Combustion engine?
The firing order heavily influences crankshaft design. In a Diesel engine, the firing order corresponds to the order in which fuel is injected into each cylinder. Four-stroke engines must also time the valve openings relative to the firing order, as the valves do not open and close on every stroke.
Related: What is Crankshaft?
Common firing orders are listed below. For V engines and flat engines, the numbering system is L1 for the front cylinder of the left bank, R1 for the front cylinder of the right bank, etc.
In a radial engine, there is 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.
Firing Order is Determined by the Number of Cylinders contained within that engine & Crankshaft Alignment/Offset of each Crank-Journal, during the Design/Manufacturing Process.
The firing order is determined when the engine is DESIGNED, so as to make it run as efficiently and as smoothly as possible. The forces and loads exerted by pistons on the crankshaft are calculated. The required counterweight is calculated. Plugging all these into the dynamic balancing equations, the firing order is determined such that, minimal vibrations are produced.
Designing Parameters of Firing Order:
The correct firing order is very important because mixing up the spark plug wires may prevent the engine from starting, cause it to backfire, and run very poorly if at all.
NOTE: On engines where two adjacent spark plugs fire right after each other, it is important to make sure the spark plug wires are not routed right next to each other for a long distance.
Related: What is Spark plugs?
This can cause a crossfire between the plugs because the magnetic field created by the spark going to one plug may fire the next plug prematurely, causing the engine to run rough and misfire. To prevent this from happening, crisscross the two plug adjacent plug wires to cancel out the magnetic induction.
On engines with distributor-less ignition systems or coil-on-plug ignition systems, the firing order is controlled by the ignition module or engine computer.
The computer receives an input signal from the crankshaft position sensor (and camshaft position sensor on some engines) to determine which piston is coming up to the top dead center on its compression stroke. It then fires that spark plug, and the next, and so on in the firing sequence.
The firing order of an internal combustion engine is the sequence of ignition for the cylinders. In a spark-ignition (e.g. gasoline/petrol) engine, the firing order corresponds to the order in which the spark plugs are operated. Firing order affects the vibration, sound, and evenness of power output from the engine.
Firing order in an engine is important because a correct firing order can cause minimum vibrations in the system. Minimum vibration in automobiles is desired as the ride can become smooth and the driver and passengers won’t feel the vibrations being transmitted by the engine as it is very less.
V8 firing order:
Straight-six engines typically use a firing order of 1-5-3-6-2-4, which results in perfect primary and secondary balance. V6 engines with an angle of 90 degrees between the cylinder banks have used a firing order of R1-L2-R2-L3-L1-R3 or R1-L3-R3-L2-R2-L1.
AMC (most V8 engines): Clockwise 1-8-4-3-6-5-7-2.
In 4 stroke engines firing order 1–3–4–2 is most commonly used than other orders because it delivers more smooth and efficient power output. The reason is let’s divide the flywheel into 4 equal parts. Means from 0°to 90°power is generated by cylinder no 1 and likewise up to 360°or 0° by 4 cylinders.
The firing order of an engine is the sequence in which the power event occurs in the different cylinders. The firing order is designed to provide for balance and to eliminate vibration to the greatest extent possible.
4-Cylinder Engines: In the case of 4-cylinder engines, the crankpins are 90 degrees apart. So, manufacturers use 1-3-4-2 or 1-2-4-3 as firing order for 4-cylinder engines.
You cannot change the firing order as it is already set out in the design of the crankshaft and cam shaft relationship. The usual firing order of a 4 cylinder in line engine would be 1,2,4,3. but it could also be designed as 1,3,4.2 which is the reverse firing order.
When the firing order is wrong or delayed, the engine does not run properly. The spark may be delivered to the cylinder when there is no fuel/air mixture or before it is properly compressed. One symptom of an incorrect firing order is the engine does not run. Turning the ignition does not start the engine.
Incorrectly removing or installing spark plugs can cause damage to your engine. Also, care needs to be taken when removing spark plug wires, especially if you plan to reuse them. It’s possible to damage the threads inside the engine when installing the spark plug.
The firing order starts at the distributor’s number one terminal and continues in clockwise or counterclockwise fashion until reaching the number one terminal again.
Engines with an uneven firing interval usually have a burble or a throaty, growling engine sound and more vibrations. The main application of uneven firing intervals is motorcycle engines, such as big-bang firing order engines.
The twin pulse firing order (1 – 0 degrees, 2 – 90 degrees, 3 – 290 degrees, 4 – 380 degrees) resembles the working cycle of a twin cylinder engine and provides the rider-friendly torque delivery which is at its peak from 9000 – 11,750rpm.
In the most common method for cylinder numbering of a V8 engine, when facing the engine from the front of the car, the cylinder on your actual right side and closest to you is the number one cylinder. Then jumping to your actual left side, the closest cylinder to you is the number two cylinder.
The firing order on all the 65 deg V12s, except the 456M, is 1-12-5-8-3-10-6-7-2-11-4-9. Note these are 65 deg V12s vs the 60 deg V12s of the earlier cars, if that has any bearing.
In most modern engines, ignition timing is controlled by the engine’s computer.
The most important factors are explained below.
Cubic capacity or CC of the bike is the power output of the engine. The cubic capacity is the volume of the chamber of the bike’s engine. Higher the capacity, larger is the quantity of air and fuel mixture that can be compressed to produce power.
The piston rings act to carry heat away from the hot piston into the cooled cylinder wall/block of the engine. Heat energy flows from the piston groove into the piston ring and then into the cylinder wall, where it eventually will be transferred into the engine coolant.
The spark plug wire order matters a lot. In most cases, the wires are labeled with numbers that will help you match with the right cylinder. To avoid mixing up and placing spark plug wires in the wrong cylinder, it is prudent to replace them one at a time.
In essence, the goal in changing the firing order is to create a smoother-running engine and more even fuel distribution, with the enhanced crankshaft and main bearing durability. In the process, horsepower gains may be achieved as well (no guarantees here, but in most cases, a slight power increase does result).
Firing order doesn’t affect the sound of the engine, but it does affect the sound of mechanical anger, which can be found in old Pontiacs and Ford FEs. It’s possible that it’s the exhaust ports on those two.
Yes. Everything else remains the same, if the firing order is changed, it can lead to engine troubles sooner. This is because the firing order is chosen to minimize unbalance forces acting on the crankshaft.
Most (Audi 2.5, VW 2.5 R5) five-cylinder engines have the firing order 1-2-4-5-3. Firing of one cylinder after another (e.g., 1-2-3-4-5 in case of a five-cylinder engine) is never used except in 3-cylinder engines where there is no alternative and in some V6 engines.
