Spark plug gap | Spark Plug Gap Chart (2023)

Adjusting the spark plug gap is important for proper engine operation. To properly set the spark plug gap, you must use aspark plug gap tool🇧🇷 For reference see our spark plug gap table below, this table converts metrics into standard measurements.

How do you change spark plugs- Spark plug gap adjustment and gap cross reference table

Spark Plug Gap Cross Reference Chart - Metric to Standard (mm to Inches)


The most important rule when checking or adjusting the spark plug gap is never to apply force to the center electrode of the spark plug or the ceramic insulator of the center electrode. Force should ONLY be applied to the spark plug ground electrode strip by moving it toward or away from the spark plug center electrode. The spark plug gap should not be changed more than three times and should not exceed 0.008" in any direction. Changing the spark plug gap too much will weaken the spark plug mass and may also affect the spark plug gap and should never exceed 0.055" unless otherwise specified by the manufacturer.

Most brisk and non-brisk spark plugs are preset at around 0.75mm - 0.8mm. If your spark plug part number does not have any trailing digits, it will default (for most part numbers) to that specification. Exceptions are e.g. B. Part numbers of spark plugs with play that do not need to be adjusted and cannot be changed, e.gBrisk premium multi-spark spark plugs,LGS Premium Brisk spark plugs, Live premium LGS-T spark plugs,Extra fast turbo spark plugsja few others. That "-T" denotes an LGS spark plug with anarrow gapthan the standard LGS spark plug and should be used in applications where the recommended gap setting is less than 0.032". 1.3mm NGK BKR6E-11 Gap Size 1.1mm Denso T16EPR-U15 Gap Size 1.5mm, Champion RC10YC4, Gap size is 1.0mm.) The part numbering for Brisk, NGK and Denso spark plugs is fairly logical, with subsequent digits translating directly into mm. For Champion spark plugs it is a little less logical and is listed below:

4 = 1,0 mm (z. B. RC10YC4)
5 = 1,3 mm (zB RN16YC5)
6 = 1,5 mm (z. B. RS14YC6)

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Electrode gap: Understand the basics

The spark plug gap is where the spark plug discharge is supposed to take place. On a conventional spark plug, this is the area between the center and ground electrodes. Since the spark always follows the path of least resistance, the spark gap is usually the narrowest point between the spark plug center electrode and the spark plug ground electrode, which is sometimes formed by the spark plug boot itself. The only case where the spark will take a longer path to ground is when the longer path is more conductive (offers less resistance). This could e.g. This can be attributed, for example, to the loss of the insulating properties of ceramics due to the deposit of conductive carbon in the combustion process (encrustation in spark plugs).

The large gap setting requires a higher voltage (electrical pressure) for the spark to jump the long gap. As a result, a higher voltage builds up in the ignition system (ignition coil, distributor, ignition cable) before the spark jumps over. This is generally desirable in high horsepower new model ignition coil applications and naturally aspirated, low compression engine applications where cylinder pressures are relatively low and spark discharge can easily occur.

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However, if you are running a large gap in the cylinder by applying high pressure (making it very difficult for a spark to occur), then such a high voltage (electrical pressure) is required for the spark to jump the spark plug gap that the spark finds one Socket in a simpler way. to jump. the ground, possibly where the spark wire is near the ground (engine block, etc.), etc. In either case, there will be no spark between the spark plug electrodes in the combustion chamber and the engine will misfire.

Typically, low cylinder pressure (low compression ratio) applications operating with lean A/F (air/fuel) mixtures have a large recommended clearance (approx.Turbo, supercharged, nitrous applications,...) require less than 0.032" spark plug gap. A dense A/F mixture is much harder for the spark to penetrate and requires a much higher voltage (pressure). Higher fuel concentration has the same effect (A/F. This Because of this, high horsepower vehicles (1,000hp or more) often have spark plug gaps as short as 0.016". Despite being fitted with some of the most powerful ignition systems capable of delivering over 60,000 volts of high current and mJ of output power.

Sometimes customers wonder why there are so manydifferent spark plug ignition settings🇧🇷 Because in order to achieve the best possible performance, spark plugs must be carefully matched to the correct application and intended use. "Experts" often say that there is no difference in spark plugs and the mixture ignites or not. You couldn't be further from the truth! Even modern OBD-II (On-Board Diagnostics) engines in standard vehicles can determine crankshaft angular velocity from a simple crankshaft position sensor. A trigger wheel is mounted on the crankshaft and has many teeth. As the crankshaft turns, this trigger wheel induces a pulse as each tooth passes the sensor. If each cylinder produces exactly the same amount of energy, the time between each pulse will follow the same pattern. However, if a cylinder produces slightly less energy, the time between the corresponding pulses increases slightly. This is calculated as % misfire. Modern engines often flash the check engine light with a misfire code (usually P03xx) with the corresponding cylinder number when even a 10% misfire occurs, which takes a long time before anyone feels anything bad or even thinks it's a misfire. occurrence

A great deal of performance can be achieved by using the correct spark plug for a particular application, as well as by installing a new spark plug set. Up to 20 hp just by replacing used spark plugs is not uncommon. Used spark plugs are difficult to ignite due to worn gaps and the deterioration of the ceramic's insulating properties due to solid combustion residue and old fuel saturation. This robs the spark plug gap of available voltage as it "leaks" through the low resistance carbon deposits into the ground resulting in a weak spark. Think of a worn spark plug gap like an old and leaking water hose that requires more water pressure and is like restricting the flow with your finger at the end. The leaking hose requires more pressure because more water is leaking from places other than the end of the hose.

there are many differencesspark plug gap stylesavailable, partly withlow fission capacity, some with high fission capacity, some withlow ignition voltage requirement, some with high ignition voltage requirements, some with a protruding tip, some with a retracted tip,sometimes at a fixed distance, some with adjustable spark plug gap, some withseveral parallel holes, some withseveral holes in a row.

For the best engine and spark plug performance, the size, style, and shape of the spark plug gap must match many factors. Some of them are:

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1) Ignition System Potential: Ignition voltage (sometimes referred to as voltage potential or electrical pressure) is the distance that the spark can travel at a given barometric and ambient pressure (A/F (air/fuel) mixture concentration, etc.) . .between the spark plug gap (center electrode and ground electrode).

2) Pressure in the combustion chamber at the time of spark discharge - It depends on the compression and intake of the engine. High compression and turbocharged engines have higher combustion chamber pressures at the time of spark discharge. Higher cylinder pressure requires higher voltage for sparking to occur.

3) Fuel Type and Concentration: For example, fuels with high alcohol content require a lower A/F ratio and closer spark plug gaps.

4) Pre-ignition point of the engine - the closer the spark is to TDC (top dead center) of the engine, the greater the pressure of the A/F mixture to ignite and the harder it is for the spark to spark.

5) Engine load and intended use: When the engine is loaded, the pressures in the combustion chamber are higher because more air is sucked in, making spark formation more difficult. High RPM applications also reduce ignition coil saturation (on time or DWEL), making less power available.

6) Type of ignition system: magneto, DC (capacitor discharge) or inductive. DC sparks have a very fast voltage rise (short rise time) and therefore also work very well with high-capacitance spark plugs such as multi-gap spark plugs and/or surface discharge spark plugs. On the other hand, inductive ignition systems generally provide a longer spark duration...

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Spark plug heat range

Production vehicles (which are not further modified to increase performance) with engines that are properly tuned and in good technical condition can be equipped according to the current application tables.

All spark plug comparison charts are for informational purposes only and do not replace the current application charts in their entirety.

When increasing the power of the engine through additional modifications, it is advisable to contact a representative of the manufacturer. The principle always applies that with medium performance conversions it makes sense to use 2 degrees "cooler" candles than with the original equipment (e.g. change from 15 to 12). After several kilometers of driving and evaluating the appearance of the insulator tip, it is possible to decide on the most suitable equipment. This operation requires a lot of experience.

Correct length of threaded spark plug boot

When changing spark plugs, always ensure that the threaded portion of the spark plug housing (from the spark plug seat) is the same length (or very close) to the O.E. Spark plug.

If the threaded section is slightly longer, spark plug washers can be used to obtain the desired spark plug reach.

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Spark plug gap | Spark Plug Gap Chart (1)


How exact do spark plug gaps need to be? ›

Most engine builders seem to settle around 0.035 of an inch. Factors such as the type of ignition you run, cylinder heads, fuel and even timing can affect how much gap will work best for you. Generally, you want as much gap as you can get by with to ensure ignition each time the plug fires.

Is it better to have a bigger or smaller spark plug gap? ›

A smaller gap will yield a short, intense spark and will usually make the engine real responsive. A wide gap creates a longer spark arc but without sufficient "juice" from your ignition system, (including amps), it can be weak and yellow in color.

What happens if plug gap is too small? ›

The Spark-Plug Gap

If the gap is too small, the spark will likely be too weak and cause the engine to run poorly or with poor efficiency.

Do spark plugs have to be perfectly gapped? ›

A properly gapped spark plug is necessary for a properly functioning engine. The gap size affects the spark plug's firing temperature, which has a direct relationship to the combustion of fuel and air in the engine.

What happens if the spark plug gap is too big? ›

Many think the larger the gap, the better. However, if the gap is too large, and the ignition system can't provide the voltage needed to spark across the gap, or turbulence in the combustion chamber blows out the spark, misfires will occur.

How do you know if spark plugs were put in wrong? ›

If the spark plug fires at the wrong time, this could lead to constant rattling, pinging, or knocking sounds. Hard vehicle start. If your car is having trouble starting or just feels disjointed and jerky, your spark plugs may not be working right, and this can lead to misfires and erratic performance.

What is the most common spark plug gap? ›

Spark plugs in automobiles generally have a gap between 0.6 and 1.8 mm (0.024 and 0.071 in). The gap may require adjustment from the out-of-the-box gap.

Do Iridium spark plugs need to be gapped? ›

Iridium Power Gapping Tips

In most cases your Iridium Power plugs do not need to be gapped. Even with small variations in the factory set gap the ultra-efficient firing power design will compensate for those small variations.

What is the best spark plug gap for fuel economy? ›

The optimum gap between 0.7 to 0.9 mm. At 0.4, 0.5, 0.6, and 1mm made more fuel consumption. Using platinum spark plug and RON 90 fuel can reduce fuel consumption to 5% on average.

How many times can you gap spark plugs? ›

Step 4: Check The Gap Again

Repeat the adjustment until the gap tool fits closely between the spark plug electrodes. However, you shouldn't adjust the ground electrode more than 3 times.

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.

How often should spark plugs be changed? ›

Ordinary copper and nickel spark plugs should be changed every 30,000 to 50,000 miles, unless otherwise suggested by the spark plug manufacturer. Platinum and iridium spark plugs tend to last longer than standard copper and nickel spark plugs. Expect to change them every 60,000 to 150,000 miles unless otherwise noted.

Should I replace ignition coils with spark plugs? ›

Worn spark plugs can cause unnecessary load on the coils and there is often some overlap in the labor required to replace both components. If your ignition coils failed as a result of worn-out spark plugs, it is wise to replace both components at the same time.


1. How to Gap a Spark Plug
2. Spark Plugs 101, Reading and Gapping : Pro Tip
(J&P Cycles)
3. What is spark plug gap? [TECH BIT TUESDAY]
(Built On Purpose)
4. How to Gap Iridium Spark Plugs
(Ian Karr)
5. The Spark Plug Gap Is NOT Critical (With SHOCKING Proof)
(Steve's Small Engine Saloon)
6. How To Check And Set Spark Plug Gap
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