GM Firing Order: The Ultimate — LS vs Small Block, V6 & Inline, Interactive Animation, Safety, Pros & Cons, and How-To
🏁 2. Complete Types of GM Firing Orders (By Engine Family)
🔹 Classic GM V8 (Small/Big Block)
1-8-4-3-6-5-7-2
Cylinder numbering: left bank (driver side) 1-3-5-7 front to rear; right bank 2-4-6-8. Gen I, II, Mark IV, Vortec 350, 454, 502.
🔹 GM LS / LT (Gen III-IV-V)
1-8-7-2-6-5-4-3
Improved crankshaft journal overlap → less stress. LS1, LS3, L83, L86, LT1, LT4, LSA.
🔹 GM 60° & 90° V6
1-6-5-4-3-2 (Buick 3800, Chevy 4.3L Vortec)
Also 1-2-3-4-5-6 on some older V6? rarely – always verify.
🔹 GM Inline-6 & 4-Cylinder
GM 4.2L Atlas I6: 1-5-3-6-2-4
Iron Duke 2.5L I4: 1-3-4-2 (most GM 4-cyl use 1-3-4-2).
| GM Engine Code | Firing Order | Applications |
|---|---|---|
| Small Block Gen I | 1-8-4-3-6-5-7-2 | Camaro, Corvette (pre-97), C/K trucks |
| LS1 / LS6 | 1-8-7-2-6-5-4-3 | C5 Corvette, F-Body, GTO |
| GM 5.3L (LM7, L59) | 1-8-7-2-6-5-4-3 | Silverado, Tahoe, Sierra |
| 3800 Series II V6 | 1-6-5-4-3-2 | Buick Regal, Pontiac Grand Prix |
| Chevy 4.3L V6 | 1-6-5-4-3-2 | S10, Astro, Express |
| Atlas LL8 4.2L I6 | 1-5-3-6-2-4 | Chevy TrailBlazer, GMC Envoy |
🎬 Interactive GM Firing Order Animation (Classic 1-8-4-3-6-5-7-2)
🔁 Below: animated cylinder diagram of GM classic V8 firing order. Cylinders light up in sequence: 1 → 8 → 4 → 3 → 6 → 5 → 7 → 2. This represents actual power pulses on a Chevy small block. Use controls to step through or watch the cycle.
💡 How to read diagram: Left bank (cylinders 1,3,5,7), right bank (2,4,6,8). GM’s classic order alternates firing between banks to reduce vibrations.
🔧 How to Identify & Validate GM Firing Order (Step-by-Step)
Step 1 – Locate cylinder numbering: On GM V8s, #1 cylinder is typically driver side front. On LS engines, the same rule applies. Step 2 – Know your distributor rotation: Classic small block: clockwise. Step 3 – Follow plug wire routing: For distributor engine, start with #1 terminal and follow the firing order clockwise. For coil-near-plug (LS), verify via GM service manual or ECM data. Step 4 – Power balance test: Use a scan tool to detect misfires; wrong order triggers random misfire (P0300). Pro tip: Always cross-reference with engine RPO code.
📊 Advantages & Disadvantages of GM Firing Orders
✅ Advantages
- Excellent crankshaft durability – Even loading on main bearings.
- Smooth idle & low NVH – Especially LS 1-8-7-2-6-5-4-3 order.
- Improved exhaust scavenging – Reduces charge robbing, better volumetric efficiency.
- Versatile across platforms – Marine, racing, street proven.
- Lower firing interval variations = less torsional vibration.
❌ Disadvantages / Considerations
- Confusion between classic & LS orders → frequent misdiagnosis.
- Classic order (1-8-4-3-6-5-7-2) creates higher loads on number 2 main bearing at high RPM.
- Modifying order requires expensive custom camshaft and rework.
- Wrong order leads to immediate engine damage (bent valves, melted cats).
- Non-standard firing orders reduce parts interchangeability.
🚗 Where & Why Firing Order Matters (Real Applications)
From GM crate engines to high-performance drag racing, firing order dictates power pulse smoothness. In LS swaps, using the correct 1-8-7-2-6-5-4-3 sequence ensures factory ECU compatibility. Classic restomods often retain 1-8-4-3-6-5-7-2 because aftermarket cams support it. In marine GM V8s, correct firing order prevents destructive harmonics. Also, firing order affects the sound character – LS engines have a distinct exhaust note due to different grouping.
⚙️ Deep Dive: Why GM LS Engines Use 1-8-7-2-6-5-4-3
GM engineers changed from the traditional order to improve crankshaft journal overlap. The sequence 1-8-7-2-6-5-4-3 reduces the maximum bending moment on the crankshaft by 8-10%, allowing lighter cranks. It also changes the order of cylinder firing across banks, improving intake manifold tuning. This is why LS engines rev higher and endure more stress in stock form.
