What is the spark plug gap on a 302 Ford engine?
Most 302/5.0L Ford engines use a spark plug gap of about 0.054–0.060 inches (1.37–1.52 mm).
The exact gap can vary by year, ignition system, and plug type. This article explains the typical specification, factors that can influence the setting, and how to check and adjust the gap to keep a Ford 302 running smoothly. The 302 small-block has powered everything from classic Mustangs to modern trucks, and the plug gap is a small but important detail that affects starting, efficiency, and emissions.
Typical gap for a 302/5.0L engine
The following guideline reflects the most commonly published specification for stock or near-stock 302 engines with standard ignition systems.
- Common stock gap: 0.054–0.060 inches (1.37–1.52 mm).
Always verify with the exact service manual or the plug manufacturer for your specific year and setup, as there are exceptions for certain engines and aftermarket configurations.
Factors that influence the spark plug gap on a 302
Several conditions can shift the ideal gap away from the baseline, depending on how the engine is built and operated.
- Year and ignition system: carbureted, early EFI, and late-model electronic ignition can have different recommended gaps.
- Plug type and heat range: factory versus aftermarket plugs may specify slightly different gaps.
- Compression and timing: higher compression or altered cam timing can subtly change optimal gap.
- Performance enhancements: forced induction, nitrous, or substantial fuel system changes can require adjustment.
- Fuel quality and octane: poor fuel or ignition timing issues can interact with gap to affect misfires and performance.
When in doubt, consult the vehicle’s service manual or the plug manufacturer to confirm the exact gap for your year, model, and modifications.
How to check and set the spark plug gap on a 302
Before you begin, assemble the right tools: a spark plug socket, a feeler gauge, and a gap tool. The steps below outline a standard procedure for inspecting and setting the gap.
- Turn off the engine, allow it to cool, and remove the appropriate spark plug using a spark plug socket.
- Inspect the plug for wear or fouling; replace if the electrode shows excessive wear or damage.
- Measure the gap with a feeler gauge. Compare the measured gap to the recommended specification (0.054–0.060 inches / 1.37–1.52 mm for most 302 engines).
- If the gap is too narrow, carefully bend the ground electrode outward in small increments using a gap tool or pliers, then re-measure. If too wide, gently bend the electrode back toward the center until the gap is within spec.
- Reinstall the plug and torque to the manufacturer’s specification (consult the service manual for the exact value). Improper torque can strip threads or damage the plug-seat seal.
- Repeat the process for each spark plug, then run the engine to verify smooth operation and check for any misfires.
After installing all plugs, it’s prudent to recheck a sample of plugs if you’ve altered gaps or used different plugs, to ensure consistency across cylinders.
Plug choice and ignition notes
While the gap is a single number, the overall ignition and combustion performance also depend on plug heat range, electrode design, and ignition system health. Stick with plugs recommended for your year and model, and avoid mixing plug types or gaps that aren’t matched to the engine’s configuration. In performance-oriented builds, some owners experiment with small adjustments within the published range, but any change should be tested for reliability and drivability.
Summary
For the Ford 302 (5.0L) engine, the standard spark plug gap typically falls in the 0.054–0.060 inch (1.37–1.52 mm) range. Always confirm with the specific year, ignition system, and plug manufacturer guidance, as there are exceptions. Regularly inspecting plugs for wear, using the correct heat range, and torqueing to the proper specification will help maintain reliable starts and smooth performance across the 302’s varied applications.
In the end, the gap is a small setting with outsized effects: get it right, and the engine starts cleanly, runs evenly, and meets emissions targets; get it wrong, and misfires or reduced efficiency can creep in. A quick check now and then can save time and trouble down the road.
