What is the plug gap on a small block Chevy?
In most small-block Chevys, the spark plug gap is around 0.035 inches (0.9 mm); many builders run 0.040–0.045 inches (1.0–1.1 mm) for higher compression or performance ignition systems. The exact gap depends on plug type, ignition setup, compression ratio, and fuel quality, so always verify the specification from the plug manufacturer and your engine’s intended configuration.
Typical gap ranges by configuration
The following ranges cover common SBC configurations you’re likely to encounter. Use them as starting points, then fine-tune based on performance and manufacturer guidance.
- Stock small-block Chevy with points or conventional ignition: 0.035 inch (0.9 mm)
- Modern electronic ignition or stock compression: 0.035–0.040 inch (0.9–1.0 mm)
- Performance or higher compression engines: 0.040–0.045 inch (1.0–1.1 mm)
- Extreme high-boost or specialized setups with high-energy ignition: up to 0.050–0.060 inch (1.27–1.52 mm) if the ignition system can reliably fire it
In practice, start at the lower end of the range and adjust based on how the engine runs, misfire symptoms, and plug condition. Always follow the plug manufacturer’s exact spec for your chosen plug type.
How to measure and set the gap
Use a precise feeler gauge and adjust carefully to avoid damaging the plug or electrode.
- Identify the recommended gap for your spark plug model and ignition system from the packaging or manufacturer’s specs. If unsure, start at 0.035 inch (0.9 mm).
- Remove the spark plug and inspect its condition; measure the current gap with a feeler gauge.
- If adjustment is needed, gently bend the ground electrode to increase or decrease the gap. Do not bend the center electrode.
- Recheck the gap with the gauge until you reach the target specification.
- Reinstall the plug and torque to the manufacturer’s specification for your engine and plug type (commonly around 15–20 ft-lbs for SBC, but always verify).
- Reconnect ignition components and test-run the engine; if misfires or rough idling occur, recheck the gap and plug condition.
Note: Iridium or platinum plugs can have slightly different tolerances, and plugs may arrive pre-gapped but should still be rechecked after installation.
Summary
Spark plug gap for a small-block Chevy typically centers around 0.035 inches, with many performance applications acceptable at 0.040–0.045 inches. Always verify with the plug manufacturer and your ignition system, and adjust based on compression, fuel quality, and real-world engine response. Proper gap helps ensure reliable starts, smooth idle, and optimal combustion.
