GEN V LT1 FIRING ORDER: 1-8-7-2-6-5-4-3 — TECHNICAL BIBLE (Physics, Pros & How-To)

❓ 2. Why Did GM Choose 1-8-7-2-6-5-4-3 for Gen V LT1?

During the development of the LS engine (late 1990s), GM engineers discovered that the classic SBC firing order caused uneven spacing of power pulses on the crankpins, leading to increased torsional vibration at high RPM. By reassigning the firing order to 1-8-7-2-6-5-4-3, the following benefits emerged:

• Reduced crankshaft torsional vibration: More balanced intervals between firing events on adjacent crank throws reduce stress on the damper and rear main bearings.
• Superior cylinder-to-cylinder air distribution: Alternating bank firing prevents “stacking” of exhaust pulses, dramatically improving scavenging, especially with long-tube headers.
• Enhanced main bearing oil film retention: Lower peak firing loads per journal increase bearing life under high-performance operation.
• Better knock margin: Uniform cylinder filling reduces hot spots and pre-ignition tendency.

For the Gen V LT1 (Direct Injection, high compression 11.5:1), this firing order is critical to avoid detonation while producing 460+ hp stock.

⚙️ 3. Types of V8 Firing Orders: Crossplane, Flat-Plane & Classic vs LT1

The Gen V LT1 firing order belongs to the crossplane family but with optimized pairing. Each cylinder fires exactly 90° after the previous, but the pairing reduces the “big bang” effect on main journals. Compared to the Ford Coyote (firing order 1-5-4-8-6-3-7-2), the GM LS/LT order is considered more balanced for forced induction due to less cylinder-to-cylinder interference.

🔢 4. Detailed Cylinder Numbering & Firing Interval Analysis

With each cylinder firing every 720° (two crank revolutions), the even 90° spacing eliminates the “gaps” present in some odd-fire V8s. Notably, the LT1 order pairs cylinders that are far apart in the engine (e.g., #1 and #8 are opposite ends), which reduces harmonic excitation of the camshaft.

✅ 5. Core Advantages of the Gen V LT1 Firing Order

• Lower Crankshaft Torsional Vibration: SAE papers confirm the LS/LT order reduces peak vibratory torque by nearly 18% vs classic SBC at 6000 rpm.
• Better Exhaust Scavenging: Because cylinders 1 and 7 (both on left) do not fire consecutively, exhaust pulses are evenly distributed, increasing torque by up to 15 lb-ft on performance headers.
• Increased Bearing Durability: Main bearing loads are more uniform, an advantage for boosted engines exceeding 800 hp.
• Reduced risk of detonation: More consistent EGTs across cylinders.
• Compatibility with high overlap camshafts: The firing spacing contributes to stable idle and vacuum.

⚠️ 6. Potential Disadvantages & Context

While the LS/LT firing order is superior in most metrics, some old-school enthusiasts note that the exhaust note is slightly more “even” and less irregular than the classic Chevy rumble. Additionally, retrofitting an LT1 into a pre-1996 vehicle requires a full standalone ECU that supports the 1-8-7-2-6-5-4-3 order; you cannot reuse a classic SBC distributor. Also, camshaft manufacturers produce LT-specific grinds – never install a traditional SBC cam into a Gen V LT1, as valve timing events would be catastrophic.

🛠️ 7. How to Verify Firing Order on a Gen V LT1 (Step-by-Step)

How to check and confirm your LT1 firing order: Even if the factory sets it, after modifications (coil relocation, standalone ECU), you must verify. Follow this diagnostic guide:

1. Use a scan tool with bidirectional control: (HP Tuners, Tech2) – activate each injector or coil individually while observing cylinder contribution.
2. Ignition coil harness layout: GM OEM coils are labeled. Ensure wiring order follows PCM output: output A → cyl1, B → cyl8, C → cyl7, D → cyl2, E → cyl6, F → cyl5, G → cyl4, H → cyl3.
3. Static cam/crank correlation: Remove valve cover on cylinder #1, bring to TDC compression, check cam sensor signal. Rotate crank 90° and see which cylinder’s coils fire.
4. Perform a cylinder balance test: Disable one cylinder at a time; the RPM drop should follow the 1-8-7-2-6-5-4-3 order if the ECU is correctly configured.

🏁 8. Is It Safe for Forced Induction & High RPM? (YES)

Absolutely. The Gen V LT1 firing order is one of the most robust for forced induction. Because of the reduced main bearing load variation and even cylinder pressures, many 1000+ hp twin-turbo and supercharged LT1 engines run this factory order without any modification. The sequence also minimizes “crank walk” often seen in high-clamp load applications. LT1 short blocks with stock firing order have survived 1500+ hp in drag racing.

🏎️ 9. Use Cases & Performance Applications

The 1-8-7-2-6-5-4-3 firing order is standard in Corvette C7, Camaro SS, Cadillac CT5-V Blackwing (LT4/LT1 variant). Engine swaps: popular in restomods, drift cars, and off-road buggies. Tuners prefer this order because aftermarket ECUs (Holley Terminator X, MaxxECU) natively support it. For high-performance marine engines (Ilmor), the smooth firing pattern reduces gearcase vibration.

📐 10. Advanced: Relationship Between Firing Order and Camshaft Lobe Phasing

The firing order directly determines the camshaft lobe arrangement. On a 4-stroke engine, each cylinder fires once every two revolutions. The camshaft rotates at half crankshaft speed. To achieve the LT1 firing order, the lobes on the cam are ground in a specific angular sequence: cylinder #1 intake lobe at 0°, then #8 lobe at 90° cam degrees (180° crank), #7 lobe at 180° cam degrees (360° crank), etc. Any aftermarket cam for LT/LS must follow this phasing, otherwise valves will hit pistons or firing intervals will be wrong.

📊 11. Comparative Table: Firing Order Impact on Engine Behavior