If your 1973–1987 C10 still has the factory points-style ignition or an older single-wire HEI, upgrading to a modern HEI distributor is one of the best performance-per-dollar mods you can do.
Factory Ignition on Square Bodies:
- 1973–1974: Points and condenser (delco ignition)
- 1975+: GM High Energy Ignition (HEI) with built-in coil
Why Upgrade to a Modern HEI?
The factory 75+ HEI is decent but limited:
- Factory coil output is relatively weak
- Rev limit around 6,500 RPM
- Can struggle with high-compression or cam-upgraded engines
What a Modern HEI Does:
- Higher spark voltage (more reliable ignition at high RPM)
- Better spark plug gap capability (can run wider gap for better combustion)
- Improved idle quality with larger cam
Top Pick – Replacement HEI Distributor:
Voltstorm HEI Distributor for GM SBC/BBC V8 – 65K Coil, 9000 RPM – Drop-in replacement for small block and big block Chevy. Works with all 283/305/307/327/350/400 small blocks.
Installation is Simple:
- Locate TDC (top dead center) on #1 cylinder
- Remove old distributor (mark orientation)
- Install new HEI in same position
- Check rotor pointing to #1 on cap
- Start and set timing (use timing light)
- Advance timing to 36–38 degrees total for most 350s
Timing Tips:
- Initial timing: 12–14 BTDC
- Total timing (all-in): 36–38 degrees
- Use a vacuum advance for better part-throttle economy
Important: Use HEI-Rated Wire Set
HEI runs higher voltage than points systems. Use 8mm or 8.5mm spark plug wires rated for HEI. Standard wire sets will arc internally at HEI voltage levels.
Cost:
Performance HEI distributor: $40–$120
Spark plug wires: $30–$60
Total: Under $200 for a noticeable improvement
Have you upgraded your Square Body ignition? What timing are you running?