BN16 Firing Order 1-3-4-2: Engineering & Performance

🧠 Why Is Firing Order Critical for BN16 Performance?

The BN16 engine’s 1-3-4-2 sequence directly influences:

• Engine balance: Primary and secondary forces are mathematically optimized. Any deviation creates 2nd-order vibration that can shake the vehicle at high RPM.
• Torque smoothness: Overlapping power strokes reduce gaps between combustion events, improving drivability.
• Exhaust tuning: Firing interval affects pulse timing in the exhaust manifold, impacting scavenging efficiency and turbocharger response (in turbo BN16 variants).
• Fuel economy & emissions: Correct ignition phasing ensures complete combustion and prevents raw fuel from entering the catalytic converter.

📚 Types of Firing Orders Across Engine Architectures

While BN16 adheres to 1-3-4-2, other configurations use dramatically different sequences:

• Inline-4 (most): 1-3-4-2 (or 1-2-4-3 on older British engines).
• Inline-6: 1-5-3-6-2-4 (perfect primary & secondary balance).
• V6 (60°): 1-2-3-4-5-6 or 1-6-5-4-3-2 (cross-plane style).
• V8 (cross-plane): 1-8-4-3-6-5-7-2 — classic rumble due to uneven firing intervals.
• Flat-four (Subaru): 1-3-2-4 (piston movement symmetric).

The BN16’s 1-3-4-2 represents the most widespread firing order in modern automotive inline-4 engines, balancing production costs, NVH (noise/vibration/harshness), and reliability.

🔬 Detailed BN16 Firing Order Analysis (1-3-4-2)

In BN16 engines, cylinder numbering starts from the front pulley side: #1, #2, #3, #4 in line. The sequence repeats every two engine revolutions:

Notice that no two cylinders fire consecutively in numerical order, reducing localized thermal stress. Also, cylinders #1 and #4 fire 360° apart, as do #2 and #3 — a pattern that evenly loads the crankshaft’s main journals.

🛠️ How to Verify BN16 Firing Order (Step-by-Step)

Diagnosing a suspected incorrect firing order is crucial after plug wire replacement or distributor service. Follow this professional workflow:

1. Identify cylinder #1 position: On BN16, cylinder #1 is at the timing belt/chain side (front of engine).
2. Check ignition system routing: For distributor engines, trace wires from cap. The cap should have markings: order 1-3-4-2 either clockwise or counterclockwise.
3. Use a timing light with inductive pickup: Clamp onto plug wire #1, note flash. Then move to wire #3, etc., confirming sequence.
4. Perform power balance test: With engine idling, disconnect injector or coil connector one at a time. RPM drop should be equal across cylinders. Unequal drop suggests wrong order or mechanical fault.
5. OBD-II scan: Misfire codes (P0301–P0304) can indicate which cylinder is out of sequence relative to crankshaft position.

⚠️ Is It Safe to Change the Firing Order on BN16?

Absolutely NOT safe under any normal circumstance. The firing order is not a tunable parameter; it’s mechanically encoded into the crankshaft’s crankpin arrangement and the camshaft’s lobe phasing. Attempting to alter the order (e.g., swapping plug wires on a distributor engine) will cause:

• Severe backfiring through intake or exhaust, risking fire.
• Uncontrolled detonation that can shatter pistons or bend connecting rods.
• Immediate catalytic converter meltdown due to unburnt fuel.
• Irreversible damage to the crankshaft thrust bearings due to unbalanced power pulses.

Only in bespoke racing applications with a custom billet crankshaft and reprogrammed ECU would a firing order change be considered — and that requires thousands of dollars in engineering. For all BN16 production engines, stick to 1-3-4-2.

✅ Advantages of Correct BN16 Firing Order

• Superior NVH characteristics: Reduced cabin vibration, especially at idle.
• Longevity of rotating assembly: Even firing reduces fatigue on rod bearings.
• Better scavenging in exhaust: Pulse tuning enables torque plateau across wide RPM.
• Consistent cylinder pressure: Avoids hot spots and head gasket stress.
• Simpler engine balancing: Allows twin balance shafts to cancel second-order forces effectively.

❌ Disadvantages of Incorrect Firing Order

• Engine misfire & stalling: Immediate loss of drivability.
• Exhaust backfires: Unburnt mixture ignites in exhaust, destroying oxygen sensors.
• Hydrolock risk? Not directly, but severe backfiring can damage intake manifold.
• Failed emissions tests: HC and CO skyrocket.
• Potential valve/piston interference: If timing is also disturbed, catastrophic failure.

🔧 Practical Uses of Firing Order Knowledge for BN16

• Performance tuning: Adjusting ignition timing per cylinder via aftermarket ECU (e.g., Haltech, Link) still respects 1-3-4-2 base order.
• Engine rebuilding: Setting camshaft timing marks relative to crankshaft position must align with firing order.
• Custom exhaust fabrication: 4-2-1 headers are designed based on firing intervals 1-3 and 4-2 grouping for optimal scavenging.
• Diagnosing rough idle: A vacuum gauge that fluctuates rapidly indicates possible firing order error.
• Installing aftermarket camshafts: Degreeing cams requires knowing which cylinder fires at TDC.

📊 Comparative Table: BN16 vs Other Inline-4 Firing Orders

📈 Firing Order & Second-Order Vibration Explained

Inline-4 engines like BN16 inherently produce second-order vibrations (twice crankshaft speed) due to piston acceleration differences. The 1-3-4-2 firing order does not eliminate this (that’s why balance shafts exist), but it ensures the second-order forces are symmetrical. If the firing order were changed to 1-2-4-3, the secondary force vectors would become chaotic, causing the engine to shake violently at 4000+ RPM. Thus, BN16 engineers selected 1-3-4-2 to work harmoniously with dual counter-rotating balance shafts.