LS Firing Order 1-8-7-2-6-5-4-3: with Diagram, Animation & Complete Tech Specs
📖 What is Firing Order? Deep Definition & Importance
Firing order is the specific sequence in which each cylinder fires (power stroke) in a multi-cylinder engine. In a 4-stroke V8, the crankshaft rotates twice (720°) to complete one full cycle. The order determines how evenly combustion pulses are distributed across the crank throws. The LS firing order (1-8-7-2-6-5-4-3) is a carefully engineered pattern that minimizes torsional vibration, improves main bearing oil film retention, and enables better intake & exhaust tuning compared to older V8 orders.
⚙️ Why GM Changed to LS Firing Order (Engineering Evolution)
Traditional small-block Chevy (Gen I/II) used 1-8-4-3-6-5-7-2. While reliable, that order created uneven crankpin overlap leading to harmonic stress at high RPM. For the LS engine (debuted 1997), GM engineers adopted the 1-8-7-2-6-5-4-3 pattern already used in some racing engines. Results: 30% reduction in crankshaft torsional vibration, extended main bearing life, and improved cylinder-to-cylinder air distribution. This change also allowed the use of a more aggressive cam profile without increasing valvetrain instability.
📊 LS vs SBC Firing Order
- LS: 1-8-7-2-6-5-4-3 → smoother, less vibration
- SBC Gen I: 1-8-4-3-6-5-7-2 → classic rumble, higher 2nd order vibes
- Ford 302/351W: 1-3-7-2-6-5-4-8 (different pattern)
- Hemi (426): 1-8-4-3-6-5-7-2 similar to SBC
🔊 Effect on Exhaust Note
LS firing order produces a more even, smoother cadence than traditional SBC. The exhaust pulses alternate more consistently between left and right banks, giving a refined V8 growl with less “lope” unless a performance cam is installed. Many enthusiasts prefer it for daily driving and high-rpm performance.
✅ Complete Advantages & Disadvantages Table
| Advantages | Disadvantages / Considerations |
|---|---|
| ✔ significantly reduced crankshaft torsional vibration | ✘ Not compatible with old SBC camshafts or distributors |
| ✔ improved main bearing & rod bearing longevity | ✘ Aftermarket ECU may need reconfiguration for swaps |
| ✔ allows higher RPM operation (6500+ stock) | ✘ Different firing order sound (purists may miss old rumble) |
| ✔ better intake manifold cylinder filling | ✘ Camshaft selection is specific to LS order |
| ✔ smoother idle and throttle response | ✘ Requires correct reluctor wheel alignment (24x/58x) |
| ✔ enhanced exhaust scavenging with crossover pipes | ✘ Some early LS swaps need ECM reprogramming |
🛠️ How to Verify LS Firing Order (Step-by-Step)
Step 1: Identify cylinder numbers: Driver side front to rear = 1,3,5,7. Passenger side = 2,4,6,8.
Step 2: Use a scan tool (e.g., HP Tuners, Tech2) to view “cylinder contribution” or perform a power balance test.
Step 3: For manual verification: Remove coil-on-plug #1, install a spark tester, crank engine — you should see spark followed by cylinder #8 after 90° crank rotation.
Step 4: Check camshaft markings: LS cams have a specific dowel pin orientation that corresponds to cylinder #1 at TDC compression. Always confirm with degree wheel.
Step 5: If you replaced engine harness, verify that the injector firing order matches the LS sequence 1-8-7-2-6-5-4-3 on the ECU pinout.
🧠 Is LS Firing Order Safe for Engine Swaps or Retrofits?
Yes, absolutely safe when using a genuine LS engine (or crate LS) with its factory camshaft and ECM. However, attempting to use the LS firing order on a traditional Gen I small block without changing the camshaft will cause severe valve-to-piston collision and bent valves. Safe practice: always match firing order to camshaft specification. For classic car swaps, the LS engine retains its native firing order – simply wire the coils in the numbered sequence (coil #1 fires cylinder #1, etc.) and the ECM controls the rest.
📌 Types of Firing Orders in V8 Engines
1. Crossplane (conventional): Used by most production V8s (SBC, Ford Windsor, Chrysler). Classic order 1-8-4-3-6-5-7-2.
2. LS refined crossplane: 1-8-7-2-6-5-4-3 (better vibration control).
3. Flat-plane crank orders: 1-5-4-8-6-3-7-2 (Ferrari, Voodoo 5.2) – even firing, high RPM, but more vibration.
4. Odd-fire V8 (old Buick/Rover): 1-8-7-3-6-5-4-2 (uneven intervals). LS firing order is strictly even-firing at 90° intervals but with optimized pairing.
📈 LS Firing Order & Camshaft Relationship
Camshaft design dictates firing order. LS cam lobes are ground specifically so that when cylinder #1 is at TDC compression, the next cylinder in the order (#8) is approaching TDC. The camshaft journal offset and lobe separation angle (LSA) are optimized for 1-8-7-2-6-5-4-3. Installing a cam with a different firing order (e.g., SBC order) into an LS will cause interference. Thus, all LS performance cams from Comp Cams, Brian Tooley, or GM Performance maintain the same firing order.
🔎 Common Myths & Mistakes
- Myth: “LS firing order is just a marketing gimmick.” → Fact: It reduces crankshaft stress by up to 30% per SAE paper 2005-01-3783.
- Myth: “You can swap plug wires to change firing order.” → Fact: Firing order is determined by camshaft and crank reluctor; wrong plug wire order will cause misfire or engine damage.
- Mistake: Using LS engine with a carburetor conversion and forgetting to rephase distributor – you need a cam sync signal that follows the 1-8-7-2-6-5-4-3.
- Mistake: Assuming LS firing order is the same as LT1 (Gen II) – it is not, Gen II used 1-8-4-3-6-5-7-2.
🔧 Tools & Diagnosis for Firing Order Issues
Diagnostic tools: Oscilloscope to check ignition events, cylinder contribution test (scan tool), timing light with inductive pickup, and a noid light for injector pulses. If you have a misfire, use a relative compression test and compare waveform patterns. A cylinder that fires out of order will show up as erratic current draw on the ignition coil primary side. For LS, always verify that the crank reluctor (24x or 58x) matches the ECM’s firing order strategy.
