Recommended Spark Plugs and Gap Settings for Tuned 3.3T Engines

Our Recommendation

We recommend running the HKS M45IL plugs at their out-of-the-box gap of 0.028", as this is ideal for most moderate-to-aggressive street tunes.

🔧 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

In most cases, 0.028" works well across a wide range of setups—whether you're on pump gas, E85, or running methanol injection. There's no need to change the gap unless you're experiencing spark blowout or misfires under load.

That said, here’s how we approach gap adjustments when necessary:

• Pump gas / moderate boost: 0.028" (no change needed)
• E85 or higher boost setups: Start with 0.028", close to 0.026" only if you experience blowout
• Methanol injection setups: Start with 0.028", close to 0.024–0.022" only if blowout occurs at high RPM / high load

We recommend never going tighter than 0.022", unless specifically instructed by your tuner. Always use the widest gap your setup can reliably support.

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 HKS M45IL for reliable ignition on tuned 3.3Ts.
• Run 0.028" out of the box unless issues arise—verify with a proper feeler gauge.
• Tighten the gap only if you're experiencing spark blowout, and never go below 0.022".
• Both overly wide and overly tight gaps can cause misfires—match your gap to your fuel, boost, and driving style.