Recommended Spark Plugs and Gap Settings for Tuned 3.3T Engines

Our Recommendation

We recommend running either plug at 0.022" on a tuned car. Note that the HKS M45IL ships around 0.028" out of the box — verify and regap before install; OEM plugs need the same check.

🔧 Always verify the gap with a proper feeler gauge, not a coin-style tool. Coin-style gappers can damage the fine iridium tip, reducing plug life or causing poor ignition. Grab a proper feeler gauge here

Understanding Spark Plug Gap

The gap is the distance the spark must jump to ignite the air/fuel mixture. Getting this wrong can lead to misfires—either from spark blowout or weak ignition.

Misfires from Improper Gapping

• Too wide (e.g., 0.030"+):

  • Spark may blow out under high boost or load
  • Misfires at WOT or high RPM
  • Inconsistent ignition with ethanol/methanol

• Too tight (e.g., < 0.022"):

  • Weak or delayed ignition spark
  • Misfires at idle, low and high load
  • Incomplete combustion, especially on pump gas
  • Cold-start issues or hesitation

A tighter gap improves spark strength under pressure, but if it's too tight, the spark kernel becomes small and less effective—leading to poor combustion at low RPM or part throttle.

Ideal gapping is about finding the widest reliable gap for your setup. Go tighter only if you're seeing signs of blowout.

Recommended Gap Range

For tuned setups, 0.022" is our recommendation across the board — pump gas, E85 blends, or methanol injection. Boost raises cylinder pressure, and the tighter gap keeps the spark from blowing out under load instead of waiting for misfires to tell you it's happening.

How that maps to different setups:

• Stock or very lightly tuned: Factory-style wider gaps (up to ~0.028") are fine — blowout pressure isn't there yet
• Tuned — pump gas through E85 and methanol: 0.022" — set it and forget it

We recommend never going tighter than 0.022", unless specifically instructed by your tuner.

Why Gap Affects Power & Reliability

A properly gapped plug ensures the spark is strong enough to ignite the mixture reliably, while also allowing the flame kernel to grow efficiently. Ethanol and methanol are harder to ignite and require higher ignition energy, which is why tighter gaps are often used in those setups—but they come at the cost of low-speed performance if you go too far.

In a gasoline-only setup, a slightly wider gap may improve idle stability, low-end torque, and fuel economy. That's why it's always best to gap for your setup, not just your peak power goal.

Summary

• Use an OEM plug or the HKS M45IL for reliable ignition on tuned 3.3Ts.
• Gap either one to 0.022" on a tuned car — verify with a proper feeler gauge (the M45IL ships wider, around 0.028").
• Never go below 0.022" unless your tuner specifically instructs it.
• Both overly wide and overly tight gaps can cause misfires—match your gap to your fuel, boost, and driving style.