What is the recommended spark plug gap?

There is no universal number that fits every engine. The correct gap depends on your specific engine design and the spark plug type. For most gasoline engines, the gap typically falls within a broad range of about 0.028 to 0.060 inches (0.7 to 1.5 millimeters). Always verify the exact specification in your vehicle’s owner’s manual or on the spark plug packaging.

Why the gap matters and how it's chosen

The gap is the distance between the center electrode and the ground electrode. It determines how much voltage the ignition system must deliver to create a spark, which in turn affects ignition reliability, fuel efficiency, and emissions. Engines with different compression ratios, ignition systems, and plug heat ranges require different gaps; using the wrong gap can cause misfires or excessive electrode wear.

Where to find the exact specification

The definitive source for your gap is the vehicle’s owner manual or service data. Spark plug manufacturers also publish gap specs for each plug design and heat range. If you install an aftermarket plug, check both the engine’s required gap and the plug maker’s recommended gap to ensure compatibility.

These general ranges reflect what many engines require, but they are not a substitute for OEM instructions.

• 0.028–0.040 inches (0.7–1.0 mm): common on a wide range of modern and older engines with moderate compression.


• 0.040–0.060 inches (1.0–1.5 mm): typical for higher compression or certain performance-focused setups.

After selecting the correct gap, verify it with a precise feeler gauge and install the plug using the proper torque specification. If the gap is significantly off, replace the plug rather than force an improper adjustment.

Important cautions about re-gapping

Re-gapping can be risky, especially for platinum or iridium plugs, which are engineered for a specific electrode geometry and lifetime. If you must adjust, make only a small change and use the correct tools. When in doubt, replace the plug to preserve performance and reliability.

How to check or set the gap

Before you begin, have the exact gap specification on hand. Use a precise feeler gauge to measure and adjust the gap as needed.

1. Confirm the exact gap spec for your vehicle and plug type (owner’s manual or packaging).


2. Measure the plug gap with a feeler gauge and compare to the spec.


3. If adjustment is allowed for copper-core plugs, gently bend the ground electrode to widen the gap in small increments; for platinum/iridium plugs, avoid re-gapping and replace if out of spec.


4. Thread the plug by hand to prevent cross-threading, then tighten to the manufacturer’s torque specification.


5. Re-check the gap after torquing to ensure it remains correct.

Always handle plugs carefully—damaged threads, cracked ceramic, or signs of overheating mean the plug should be replaced rather than re-gapped.

Summary

The recommended spark plug gap varies by engine, with a general practical range of about 0.028 to 0.060 inches (0.7 to 1.5 mm). The exact value must come from the vehicle’s manual or the plug manufacturer’s guidance. Use a proper gap gauge, apply the correct torque during installation, and replace plugs if the gap is far from spec or the plug shows damage. When in doubt, consult a qualified technician to ensure optimal ignition performance and engine longevity.

What should I set my spark plug gap to?

The ideal spark plug gap varies by vehicle, but most are between 0.0280.0280.028 and 0.0600.0600.060 inches, with specific gaps listed in your vehicle's owner's manual. Generally, larger gaps are for lower cylinder pressures, while smaller gaps are needed for high-pressure or high-performance engines to ensure a strong enough spark. 
This video demonstrates how to check and set a spark plug gap: 1mJB ReviewsYouTube · Jul 31, 2023
Factors that influence spark plug gap

• Engine type: Naturally aspirated engines often perform better with a gap of 0.0300.0300.030 to 0.0350.0350.035 inches, while high-compression or forced-induction engines (like those with a turbo or supercharger) require a smaller gap, often below 0.0320.0320.032 inches.
• Engine performance: A larger gap requires more voltage to jump, so a smaller gap is often used for high-power applications where the air-fuel mixture is denser and more difficult to ignite.
• Horsepower: Very high-horsepower vehicles may use gaps as small as 0.0160.0160.016 inches to ensure reliable ignition. 

How to find the correct gap

• Consult your owner's manual: This is the most reliable source for the correct spark plug gap specification for your specific vehicle. 
• Use an online tool: Many auto parts stores and spark plug manufacturers have online catalogs that can help you find the correct gap based on your car's make, model, and year. 

Why the gap is important

• Engine performance: An incorrectly gapped spark plug can lead to poor fuel economy, reduced power, and higher emissions.
• Prevent damage: A gap that is too large can strain the ignition coil, while a gap that is too small can lead to incomplete combustion. 

How to adjust the gap

• Use a spark plug gap tool to measure the current gap. 
• If the gap is too wide, gently use the tool to pry the ground electrode slightly wider. 
• If the gap is too narrow, gently use the tool to tap the ground electrode against a hard surface to narrow it. 
• Re-measure the gap after making any adjustments to ensure it is correct. 

Does gapping spark plugs increase horsepower?

Side gapping spark plugs has been use in racing for years to increase horsepower by unshrouding the spark thus allowing the flame created to propagate faster resulting in a more complete burning of the fuel/air mix.

What happens if the spark plug gap is too big?

If a spark plug gap is too big, the ignition system has to work harder to jump the gap, which can lead to misfires, reduced performance, poor fuel economy, and potential engine damage. The ignition coil has to generate a higher voltage to create the spark, which can overheat it and the control module.
 
Problems caused by a gap that is too big

• Misfires: The spark may not consistently jump the gap, especially at higher speeds, causing the engine to misfire. 
• Reduced performance: The fuel/air mixture may not ignite properly, leading to a loss of power and efficiency. 
• Ignition system strain: A larger gap requires more voltage, which can cause the ignition coil to overheat and potentially fail. 
• Incomplete combustion: The timing of the spark can be effectively retarded, preventing the mixture from burning completely. 
• Potential engine damage: Consistent issues like misfires and detonation can lead to long-term engine damage. 

This video demonstrates how to gap a spark plug: 49sJB ReviewsYouTube · Jul 31, 2023
How to fix it

• Check the manufacturer's specifications: Always consult your vehicle's owner's manual for the correct spark plug gap.
• Adjust the gap: Use a spark plug gapping tool to measure and adjust the gap. You can gently pry up the ground electrode to increase the gap or tap the spark plug on a hard surface to decrease it. 
• Use a feeler gauge: For the most accurate measurement, use a feeler gauge to check that the gap is within the manufacturer's recommended range.