Which NGK spark plugs are recommended for a Chevrolet Corvette C5?

For a C5 Corvette, the right NGK spark plug depends entirely on your engine's modification level and whether you prefer the performance of a copper plug or the longevity of an iridium plug.

Here is the breakdown based on what works best for this platform:

Stock to Mildly Modified (Bolt-ons)

If your engine is stock or just has basic bolt-ons like an intake and exhaust, you want a plug in the "5" heat range.

• Copper (NGK TR55 or TR5): Copper plugs provide an excellent, hot spark, but you'll need to change them out roughly every 25,000 miles ².
  • If you want the factory-style 0.055" gap, get the NGK TR55 (Part # 3951) ⁹.
  • If you prefer a tighter 0.040" gap, buy the NGK TR5 (Part # 2238) ⁹. These are the exact same plug, but if you try to gap a TR55 down to 0.040", the ground strap will bend too far and shroud the electrode ¹¹.
• Iridium (NGK TR5IX): If you want a plug you can install and forget about for 50k–100k miles, go with the NGK TR5IX (Part # 7397) ¹³.

Heavily Modified (Heads/Cam, Boost, or Nitrous)

Once you cross the threshold of adding 100+ horsepower over stock, NGK recommends dropping one heat range colder to prevent detonation ⁸.

• Copper: Go with the NGK TR6 ².
• Iridium: Use the NGK TR6IX (Part # 3689) ¹⁰.

Replacement Advice (Difficulty: Easy to Moderate)

Swapping plugs on an LS1/LS6 is generally a 30-minute job, but it can quickly turn into a multi-hour headache if the old spark plug wires are heat-cycled and welded to the plugs ².

If this is the first time the plugs are being changed, expect the original wires to break during removal ⁴. It is highly recommended to replace the wires at the same time. The community consensus favorite for this is the GM Performance (GMPP) Red Wires (Part # 12495519) ¹³. They are high quality, priced reasonably, and feature an angled boot that helps clear aftermarket headers if you have them installed ⁸.