GM LS Firing Order 1-8-7-2-6-5-4-3
Definition, Diagram, Animation, Advantages, Safety & Full Technical Deep Dive

🔧 Why GM LS Uses 1-8-7-2-6-5-4-3 (Engineering Reasons)

GM engineers switched from traditional small-block Chevy firing order (1-8-4-3-6-5-7-2) to the LS order for key benefits: reduced crankshaft torsional vibration (less stress on main bearings), improved cylinder-to-cylinder air distribution enabling high-flow intake manifolds, better exhaust scavenging due to alternating bank firing, and enhanced torque curve especially in mid-range. The LS order also allows a simpler crankshaft counterweight design, reducing rotating mass.

🧬 Types of Firing Orders (Cross-plane vs Flat-plane)

Most V8 engines use either cross-plane crankshaft (common in American V8s, including LS) with uneven firing intervals that produce the classic rumble, or flat-plane crankshaft (Ferrari, Voodoo) with even 180° intervals. Within cross-plane engines, two dominant orders exist: the GM LS order (1-8-7-2-6-5-4-3) and the traditional SBC/Ford Windsor order (1-3-7-2-6-5-4-8 or 1-5-4-2-6-3-7-8 variations). The LS order is often considered superior for high-performance street/strip builds because it minimizes vibration harmonics at high RPM.

✅ Advantages of GM LS Firing Order

• Less crankshaft torsional vibration → allows lighter dampers and higher RPM reliability.
• Better intake manifold design (equal cylinder filling) → more torque and HP.
• Reduced cross-bank exhaust interference → improves scavenging, especially with performance headers.
• Smoother idle and transition → preferred for daily-driven LS swaps.
• Lower main bearing fatigue → longer engine life under forced induction.
• Supercharger-friendly — less stress on rotors/crankshaft snout.

❌ Disadvantages / Limitations

• Not compatible with old SBC ECUs — requires LS-specific cam and controller.
• Confusion during engine swaps — many mistakenly wire old SBC order, causing misfire.
• Can cause rough running if mismatched — spark plug wires/coil harness order is critical.
• Aftermarket camshafts must respect this order (all LS cams are ground for 1-8-7-2-6-5-4-3).

🛠️ How To Check / Verify LS Firing Order (Step-by-Step)

Step 1: Identify cylinder #1 (driver side, front-most cylinder). Step 2: Refer to LS cylinder numbering: left bank 1-3-5-7 (front to rear), right bank 2-4-6-8 (front to rear). Step 3: Remove coil harness or spark plug wires and verify the sequence from ignition coils or distributor-less ignition system follows 1 → 8 → 7 → 2 → 6 → 5 → 4 → 3. Step 4: Use a timing light on each wire while cranking (or with engine running) — the flash order should match firing order. Alternatively, use an oscilloscope on crank and cam sensors to confirm pattern. Pro tip: Many LS swap harnesses label coil outputs; check continuity if uncertain.

⚖️ Comparison: LS Firing Order vs Traditional SBC vs Ford Coyote

🏁 Use Cases: Where LS Firing Order Shines

1. LS Swaps into classic cars (Camaro, C10, Miata, RX-7) — retains factory reliability with aftermarket ECUs. 2. High-performance street/strip builds — the firing order reduces harmonics, allowing 7000+ RPM. 3. Boosted applications (twin-turbo, supercharged) — minimal cross-bank pressure interference. 4. Marine and off-road — smooth idle and torque make LS ideal for boats and buggies.

❓ What Happens If You Wire LS Firing Order Incorrectly?

Wrong firing order (e.g., using old SBC 1-8-4-3-6-5-7-2) results in severe misfire, backfiring through intake or exhaust, loss of power, possible engine stalling, and unburnt fuel damaging catalytic converters. In LS engines, it may also trigger crankshaft position correlation codes. Always double-check cylinder numbering and coil wiring diagram.

📊 Effect on Engine Balance & Crankshaft Design

GM LS firing order spaces the firing impulses every 90° of crankshaft rotation, but the sequence specifically avoids two consecutive firings on the same bank, reducing rocking couples. This allows LS crankshafts to have smaller counterweights, reducing parasitic loss. Compared to the older SBC order, the LS order lowers peak torsional stress by approximately 15-20% at similar power levels, according to GM technical papers.

🔁 Detailed Firing Sequence Table (Cylinder-by-Cylinder)

Note: 720° = full engine cycle. The sequence repeats every two revolutions.

🧠 Frequently Asked Questions (Expanded FAQ)