Comp Cams 35-512-8 Firing Order: Technical Encyclopedia (1-8-4-3-6-5-7-2) (1-8-4-3-6-5-7-2)
📊 2. Full Technical Specifications (Comp Cams 35-512-8)
🤔 3. Why Does Firing Order Matter? (Engineering & Performance)
The firing order directly affects engine balance, crankshaft fatigue, intake manifold tuning, and exhaust scavenging. The 1-8-4-3-6-5-7-2 order provides an even 90° crankshaft interval between power strokes, which reduces torsional vibration and improves main bearing life. Furthermore, it alternates between cylinder banks (left-right-left-right), giving a smooth idle and allowing efficient carburetor/EFI distribution. For the 35-512-8, its 114° LSA pairs with this firing order to maximize vacuum and throttle response.
⚙️ 4. Types of Firing Orders in V8 Engines & Where 35-512-8 Fits
Common V8 firing orders: Ford traditional (1-5-4-2-6-3-7-8), Ford HO/351W (1-3-7-2-6-5-4-8), Chevy / LS (1-8-7-2-6-5-4-3). The Comp Cams 35-512-8 uses the classic Chevy small-block order 1-8-4-3-6-5-7-2, which is also called the “standard SBC firing order”. Many aftermarket hydraulic rollers for Ford engines are ground on this order because it reduces stress on the thrust bearing. Always verify your engine’s cylinder numbering before routing plug wires.
🛠️ 5. How to Set the Comp Cams 35-512-8 Firing Order (Step-by-Step)
Step 1 – Identify cylinder numbering: On Chevy SBC: driver side front to rear 1-3-5-7; passenger side 2-4-6-8. On Ford 5.0L: passenger side 1-2-3-4, driver side 5-6-7-8.
Step 2 – Set #1 at TDC compression: Align timing pointer to 0° with balancer mark.
Step 3 – Install distributor with rotor pointing to #1 terminal. For HEI, rotor should align with the cap’s #1 tower after seating.
Step 4 – Connect plug wires in exact order: 1-8-4-3-6-5-7-2 (clockwise direction for Chevy, counter‑clockwise for some Ford distributors – verify rotation).
Step 5 – Start engine, set base timing (10–14° BTDC). Use a timing light; vacuum advance disconnected on carbureted setups.
Step 6 – Test drive & check for knock or misfire. Use a scan tool for knock sensor activity on EFI vehicles.
🛡️ 6. Is It Safe? Reliability & Safety Assessment for 35-512-8
Yes, the Comp Cams 35-512-8 firing order is absolutely safe when followed correctly. However, several safety caveats exist: distributor gear compatibility – in Ford engines with roller cams, you must use a steel distributor gear (bronze gears wear quickly). In Chevy applications, stock melonized gear works fine. Also, using the wrong firing order can cause backfires that damage intake manifolds or burn valves. Always verify valve spring coil bind clearance because the .480″ lift requires at least 1.250″ installed height for safety.
✔️ 7. Advantages & Disadvantages (Detailed Pro/Con)
✅ Advantages
- Massive low-end torque – perfect for trucks, towing, and street driving.
- EFI friendly – retains strong vacuum (17-19 inHg) for Speed Density/MAF.
- Reduces bearing loads – the 1-8-4-3-6-5-7-2 order lessens crankshaft flex.
- Smooth idle – 114° LSA creates a near-stock idle quality.
- Works with stock converter – no need for high-stall torque converter in most applications.
- Longevity – hydraulic rollers reduce friction and wear.
❌ Disadvantages
- Valve springs mandatory – requires COMP Cams #26918 or equivalent springs.
- Peak power limited – drops off after 5200 RPM; not for high-rpm racing.
- Potential idle surging in some EFI Ford setups without proper tune.
- Requires steel distributor gear on Ford 5.0L/351W (additional cost).
- Pushrod length may vary – some blocks require custom pushrods to achieve correct lifter preload.
🔩 8. Common Use Cases & Real-World Performance
| Engine / Vehicle | Build Modifications | Performance Gain |
|---|---|---|
| Chevy 350 (TBI / Carb) | Edelbrock Performer intake, headers, 35-512-8 | +45 HP / +55 lb-ft over stock, 2800-5200 RPM pull |
| Ford 5.0L EFI (Mustang / F-150) | GT40 heads, 1.7 rockers, 35-512-8, 24lb injectors | 300-320 RWHP, flat torque curve from 2000-5000 RPM |
| Ford 351W (Bronco/E-150) | Stock shortblock, long tubes, 35-512-8, SD friendly | Excellent towing, 420 lb-ft @ 3200 RPM (crank estimate) |
| Chevy 383 Stroker | 9.5:1 compression, 35-512-8, Air Gap intake | Strong idle, 400+ HP, very responsive |
🔍 9. How to Diagnose Incorrect Firing Order Symptoms (Troubleshooting)
Common signs of wrong order: engine cranks but backfires through intake or exhaust, rough idle with misfire counts, no power under load, black smoke from unburnt fuel. Use a cylinder balance test or power balance mode on a scan tool. If you suspect a wiring mistake, re-verify each wire from the distributor cap to the cylinder using the 1-8-4-3-6-5-7-2 sequence. Also, check for crossfiring between adjacent plug wires – use quality spiral-core wires.
🧰 10. Advanced Installation Tips & Torque Specifications
When installing the 35-512-8 camshaft: cam bearing clearance must be 0.0015-0.0030″. Use COMP Cams assembly lube on lobes and journals. Recommended valve spring seat pressure: 110-120 lbs closed, 280-300 lbs open. For timing chain, set cam timing dot-to-dot (straight up) for 110° ICL. Torque specs: cam retaining plate bolts 18-22 lb-ft; rocker arm nuts: 22 lb-ft (SBC) or 18-20 lb-ft (Ford pedestal). Always degree the camshaft to verify intake centerline: target 110° ATDC.
📈 11. Dynamic Compression & Tuning for 35-512-8
Due to the 206° intake duration @.050, the 35-512-8 works best with 9.0:1 to 10.0:1 static compression ratio. Dynamic compression ratio (DCR) typically falls between 7.8-8.3:1, allowing pump gas (87-89 octane) in most iron-headed engines. If you have aluminum heads, you can push to 10.5:1 static. For EFI tuning, add fuel enrichment in the 2500-4000 RPM range for optimal torque. For carburetors, a 600-750 CFM vacuum secondary works perfectly.
❓ Frequently Asked Questions (FAQs) – Firing Order & Comp Cams 35-512-8
What happens if I use the wrong firing order with this cam?
Severe misfiring, backfiring, potential exhaust reversion, and can even damage the catalytic converter. The engine may barely run or stall immediately. Double-check wiring using the 1-8-4-3-6-5-7-2 sequence.
Can I run the 35-512-8 on a stock Ford 5.0L with factory firing order (1-3-7-2-6-5-4-8)?
No – the cam lobes are ground for the Chevy pattern (1-8-4-3-6-5-7-2). You must rewire the distributor to match this sequence and ignore stock cylinder numbers. Many Ford owners swap to this order for smoother idle.
What is the difference between 35-512-8 firing order and LS firing order?
LS engines use 1-8-7-2-6-5-4-3, which is different. Do not mix them. The 35-512-8 is not designed for LS engines; it’s for traditional SBC and some Ford small-blocks.
Is the 35-512-8 safe for stock rotating assembly?
Yes. The powerband is mild, staying under 5200 RPM, which is safe for stock rods and cast pistons. Always check piston-to-valve clearance, especially if you mill heads or use thinner head gaskets.
How much vacuum does the 35-512-8 produce at idle?
Approximately 16-18 inHg at 750-850 RPM, which is enough for power brakes and most EFI systems (including Speed Density).
Do I need a custom tune for Ford EEC-IV with 35-512-8?
In many cases the stock tune will run fine, but a tune (like using Quarterhorse or Moates) can optimize tip-in response and idle stability. However, it is often considered “tune-friendly” without major changes.
What spark plug gap should I use with this cam?
Standard gap: .035″-.045″ for HEI/ TFI. For high-energy ignition systems, .050″ is acceptable.
Can I use this cam with a roots supercharger?
Not recommended. The 35-512-8 has too much overlap for positive-displacement superchargers; consider a blower-specific cam.
