LS1 FIRING ORDER BIBLE: 1-8-7-2-6-5-4-3
Complete Engineering Deep-Dive | Interactive Diagram | Pro Secrets
❓ Why Does Firing Order Matter So Much?
Firing order dictates engine balance, crankshaft stress, induction tuning, and exhaust scavenging. For LS1, the chosen order:
- Spaces combustion events evenly (every 90° crank rotation) → reduces crankshaft whip.
- Prevents consecutive firing on same bank → lowers intake manifold pulse interference.
- Enables aggressive cam profiles without overlapping misfire.
- Improves bearing oil film retention at high RPM (6700+ redline).
🔬 Types of Firing Orders — LS1 vs Others
✅ LS1 / LS Family
1-8-7-2-6-5-4-3
Used in: LS1, LS2, LS3, LS6, LQ4, LQ9, LT (Gen V) variations. Optimized for cross-plane smoothness.
🔁 Older SBC (Gen I/II)
1-8-4-3-6-5-7-2
Classic 350 order; uneven bearing load pattern, but iconic V8 rumble.
🏎️ Flat-Plane V8
1-5-4-8-6-3-7-2
Even firing but different crank throws; used in GT350, Ferrari; higher vibration but better high-rpm breathing.
🧠 Engineering Deep Dive: Why Did GM Choose 1-8-7-2-6-5-4-3?
GM powertrain engineers re-ordered the firing sequence to address fatigue points in the Gen I small-block. With the LS1’s deeper skirt block and stronger crank, they renumbered crank throws: traditional #2 main bearing received alternating loads from cylinders 2 & 3; by separating those events (cyl 2 and cyl 7 fire far apart), stress risers reduced. Additionally, the order 1-8-7-2-6-5-4-3 ensures that each cylinder fires exactly 90° after the previous, but the cylinder pairs (1&6, 8&5, 7&4, 2&3) are complementary for primary balance. This innovation allowed the LS1 to survive 7000+ RPM in racing applications with stock crankshafts.
📐 LS1 Crankshaft & Firing Relation
The crankshaft journals are arranged with 90° offsets. The firing order follows the pattern: front left (1), rear right (8), rear left (7), front right (2), then middle right (6), middle left (5), middle right-front (4), middle left-front (3). This prevents any two cylinders on the same bank firing within 180° interval, reducing exhaust reversion.
| Crank Angle | Firing Cyl | Bank | Load Effect |
|---|---|---|---|
| 0° | 1 | Left | Initial pulse |
| 90° | 8 | Right | Opposite side, low twist |
| 180° | 7 | Left | Balanced couple |
| 270° | 2 | Right | Alternating |
| 360° | 6 | Right | Progressive |
| 450° | 5 | Left | Even loading |
| 540° | 4 | Right | Staggered |
| 630° | 3 | Left | Closing cycle |
🛠️ How To Check LS1 Firing Order (Step‑by‑Step Verification)
- Identify cylinders: Driver side front to rear = 1,3,5,7 ; passenger side = 2,4,6,8.
- Inspect coil harness: Each coil pack (1-8) must route to spark plug of same number. The ECM fires coils in the 1-8-7-2-6-5-4-3 order based on crankshaft reluctor wheel (24x or 58x).
- Use a timing light or oscilloscope: Clamp inductive pickup on each cylinder wire sequentially; the pattern should follow the diagram.
- ECM scan tool: Modern diagnostic software can display real-time cylinder contribution events. Misfire counters that deviate indicate wrong order after swaps.
- Visual wire routing: Many LS1 intake manifolds have wire separator tabs; ensure cylinders 8 and 7 cross correctly.
Pro verification method: Disable fuel/spark and use a compression tester + ignition trigger light. Rotate engine manually; the spark should occur at each cylinder’s firing TDC in the order 1-8-7-2-6-5-4-3.
🛡️ Is It Safe To Change The LS1 Firing Order?
Unsafe for stock or mild builds. Changing the firing order without corresponding camshaft redesign (different lobe phasing and crank journal offsets) leads to violent backfires, piston-to-valve contact, bent rods, and complete engine failure. Only professional racing engines with billet cranks and custom ground cam profiles run alternative orders (e.g., 4/7 swap on LS1). The factory LS1 order is proven for reliability to 500+ hp. Never swap plug wires arbitrarily — it’s not a “tuning trick”.
✅ Advantages & ⚠️ Disadvantages of LS1 Firing Order
✨ Advantages
- ✔ Reduced main bearing wear – better oil film retention at high RPM.
- ✔ Smoother idle and less torsional vibration → engine mounts last longer.
- ✔ Superior intake manifold tuning – equal pressure waves → +10–15 lb-ft midrange.
- ✔ Compatible with advanced knock control algorithms.
- ✔ Enables aggressive camshaft profiles (220–240+ duration @0.050) without misfire.
📉 Disadvantages
- ✘ Not interchangeable with old SBC cam & ignition parts.
- ✘ Confusing for traditional hot-rodders doing LS swaps.
- ✘ Requires correct reluctor wheel (24x/58x) programming after order changes.
- ✘ Slightly different exhaust note vs classic SBC burble.
🏁 Use & Applications — Where LS1 Firing Order Dominates
The LS1 firing order is used across millions of vehicles: Corvette C5 (1997-2004), Camaro SS (1998-2002), Pontiac GTO (2004-2006), Holden Commodore, Chevrolet SSR, and countless LS-swapped classics. It’s also the industry reference for aftermarket EFI systems (Holley, Haltech, MegaSquirt) when configuring GM LS engines. Race teams use the inherent balance to spin LS1-based engines to 8000+ RPM in drift and road racing series. The same order appears in marine LS engines (Volvo Penta, Mercruiser).
📈 Firing Order & Exhaust Tuning / Sound Characteristics
The LS1 sequence creates an irregular but harmonious exhaust pulse spacing: left bank fires at 0°, 180°, 450°, 630°; right bank at 90°, 270°, 360°, 540°. This yields the “LS burble” — a throaty tone distinct from traditional SBC. Performance headers designed for 1-8-7-2-6-5-4-3 have specific primary tube grouping (e.g., cylinders 1&7, 2&8 etc.) to maximize scavenging. Tri-Y headers are popular for LS1 because of this order.
