Why many inline-four engines use the 1-3-4-2 firing order

Because a four-stroke inline-four with a 180-degree crank needs an ignition event every 180 degrees of crank rotation, 1-3-4-2 is a common firing order that alternates the two piston pairs (1/4 and 2/3), evens out torque delivery, reduces vibration and crankshaft stress, and gives clean exhaust pulse spacing; it isn’t the only valid pattern (1-2-4-3 is equivalent), but 1-3-4-2 became a widespread convention across many manufacturers.

What “firing order” means

Firing order is the sequence in which an engine’s cylinders ignite during the 720-degree cycle of a four-stroke engine. In an inline-four with a conventional flat-plane (180-degree) crankshaft, there are four power strokes per 720 degrees, so a power stroke occurs every 180 degrees. The firing order determines which cylinder fires at each 180-degree interval, shaping noise, vibration, harshness (NVH), crankshaft loading, and exhaust tuning.

Why 1-3-4-2 fits the physics of a typical inline-four

In most inline-fours, pistons 1 and 4 move together, and pistons 2 and 3 move together. At any given top-dead-center, one piston is finishing compression (ready to fire) while its partner is finishing exhaust. Because the crank turns 180 degrees between ignition events, the firing sequence must alternate between these two moving pairs. 1-3-4-2 satisfies that rule by switching between the 1/4 pair and the 2/3 pair at each event, producing evenly spaced, predictable torque pulses.

Key engineering goals that 1-3-4-2 supports

The following points outline the engineering reasons designers gravitate to 1-3-4-2 (and its mirror, 1-2-4-3) in even-fire inline-fours.

• Even 180-degree spacing: Guarantees uniform time between power strokes, smoothing torque delivery across the 720-degree cycle.
• Alternation of piston pairs: Switches between the 1/4 and 2/3 crank throws at each event, which helps distribute torsional input along the crankshaft.
• Manageable NVH: Predictable, even firing reduces vibration and harshness relative to uneven orders.
• Exhaust pulse timing: Produces regular, non-overlapping exhaust pulses that header designers can pair (typically 1–4 and 2–3) for good scavenging in 4-2-1 layouts.
• Thermal and bearing load distribution: Alternating “end” and “middle” cylinders (1 → 3 → 4 → 2) spreads heat and bending loads more uniformly across main bearings.

Taken together, these characteristics are why 1-3-4-2 became a default choice in many automotive inline-fours, delivering a reliable balance of smoothness, durability, and packaging simplicity.

Is 1-3-4-2 the only correct firing order?

No. With a conventional inline-four crank and typical cylinder numbering, there are two functionally equivalent even-fire sequences: 1-3-4-2 and 1-2-4-3. Both alternate the piston pairs and keep 180-degree spacing. Different brands and eras have used either pattern, often driven by historical design choices, ignition packaging, and exhaust manifold layouts rather than a hard performance advantage of one over the other.

How engineers arrive at a valid firing order

Deriving a firing order for an even-fire inline-four follows a simple logic dictated by crankshaft geometry and the four-stroke cycle.

1. Start with the crank: In a flat-plane inline-four, cylinders 1/4 share a throw; 2/3 share the other, 180 degrees apart.
2. Respect the cycle: A four-stroke engine completes one full cycle in 720 degrees; with four cylinders, ignitions must occur every 180 degrees.
3. Alternate pairs: The next firing must be on the opposite throw each time (e.g., 1/4 → 2/3 → 1/4 → 2/3).
4. Choose an in-pair order: Decide which cylinder within each pair goes first; this sets 1-3-4-2 or 1-2-4-3 (rotations or mirrors are equivalent).
5. Validate NVH and hardware: Simulate torsional vibration, bearing loads, and exhaust tuning to confirm acceptable behavior.

This process ensures any chosen sequence meets the even-fire constraint while aligning with packaging and performance goals.

Mechanical and acoustic implications

Because torque arrives in equal 180-degree chunks, 1-3-4-2 helps limit torsional spikes in the crankshaft and reduces cyclical bending loads on the block. Acoustically, the evenly spaced exhaust events yield a smoother, more consistent exhaust note and simplify muffler and resonator tuning. From a durability standpoint, the alternating load path benefits main bearing life and crankshaft longevity in mass-market road engines.

Exceptions and modern variations

There are notable exceptions where 1-3-4-2 doesn’t apply. Crossplane inline-fours (rare in cars, famously used on some sport motorcycles like Yamaha’s R1) use 90-degree crankpin offsets and intentionally uneven firing intervals for traction and feel; their firing orders and pulse spacing differ. Flat-fours (boxers) and V4s also use different crank arrangements and firing strategies. Regardless of architecture, the core principles—spacing, balance, torsional behavior, and exhaust tuning—still govern the choice.

Practical implications for service and tuning

For maintenance, getting the firing order wrong (coil wiring, distributor indexing, or ECU mapping on custom builds) causes misfires, backfiring, rough running, and potential catalyst and engine damage. For performance tuning, header pairing, cam timing, and ignition maps are all planned around the engine’s specific firing sequence to preserve scavenging and minimize reversion.

Summary

1342 is widely used as the firing order in conventional four-stroke inline-four engines because it delivers evenly spaced 180-degree power strokes, alternates the two piston pairs, and provides a good balance of smoothness, durability, and exhaust tuning. It isn’t unique—1-2-4-3 is equally valid—but 1-3-4-2 became a common standard thanks to its clean fit with typical crankshaft geometry and the practical goals of NVH control and manifold design.

Why is the firing order 1342?

The firing order refers to the sequence in which each cylinder receives the spark plug and ignites the fuel-air mixture. In a** 4-cylinder engine**, the firing order of 1342 means that cylinder number 1 fires first, followed by cylinder number 3, cylinder number 4, and finally cylinder number 2.

What is the firing order for 1243 and 1342?

Re: Firing order
Clockwise will give you 1243, counterclockwise will give you 1342.

Why is the firing order 1432?

Firing order for an engine is picked in the most efficent way to reduce vibrations and improve the engine balance. Most straight 4 cylinder engines use the 1-3-4-2 configuration.

What is the firing order of 1-3-4-2?

Since we are assuming a firing order of 1-3-4-2, cylinder #1 will be the first to fire or generate power. Next up will be cylinder #3 followed by cylinder #4 and then finally cylinder #2. For every 720 degrees the crankshaft turns, the camshaft turns 360 degrees causing all cylinders to fire once.