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Both the LS1 (1997–2004) and LS6 (2001–2004) in the C5 Corvette share the same spark plug thread and reach, so the real choice is metal type and heat range — copper for cost, iridium/platinum for longevity, and a colder step for modified engines. One well-known enthusiast favorite, Beru’s Silverstone S1K, was discontinued in the US years ago; it’s left off this list, with Nology’s current Silver line noted as the closest still-in-production alternative.
| # | Product | Price | Where to buy |
|---|---|---|---|
| 1 | NGK TR55 V-Power | $22.99 (set of 8) | Amazon · eBay |
| 2 | NGK TR6 (4177) | $3.75–$7.49 each | Amazon · eBay |
| 3 | NGK TR55IX Iridium IX | $7–$13 each (approx.) | Amazon · eBay |
| 4 | Denso Iridium TT (4713) | $12.49 each | Amazon |
| 5 | ACDelco 41-110 GM Original Equipment Iridium | $10.99–$13.49 each | Amazon · eBay |
| 6 | Bosch Platinum+4 (4417) | ~$10.35 each | Amazon |
| 7 | Nology Silver | ~$10.26 each | Amazon |
The picks, in detail
NGK TR55 V-Power
The stock-heat-range copper plug LS1/LS6 owners run on unmodified engines — cited repeatedly across Corvette forums as an excellent naturally-aspirated choice.
- Copper-core center electrode
- V-groove ignitability design
- Cheapest option here at under $3/plug
- Correct stock heat range for a naturally aspirated LS1/LS6
- Shorter service life than iridium
NGK TR6 (4177)
One heat range colder than the TR55 — the plug LS1TECH and Corvette forum members recommend for boosted, nitrous, or high-compression LS builds.
- Nickel-copper core
- One step colder than stock heat range
- Better fouling resistance under forced induction or high load
- Too cold a plug for a bone-stock, low-mileage engine — can foul in mild street use
NGK TR55IX Iridium IX
The iridium version of the same TR55 heat range — a direct upgrade path for owners who want longer service life without changing heat range.
- Iridium center electrode, 6x harder than platinum
- Same TR55 heat range in iridium form
- Longer service interval than the copper TR55
- No confirmed current retail price beyond older reference points — expect roughly $7–$13/plug based on comparable NGK iridium pricing
Denso Iridium TT (4713)
Twin-tip iridium/platinum design popular among C5 Z06 owners as a Denso alternative to NGK’s iridium line.
- 0.4mm iridium center electrode
- 0.7mm platinum ground electrode
- Rated to last well beyond 100,000 miles
- Confirm LS1/LS6 fitment against your specific plug gap spec before ordering
ACDelco 41-110 GM Original Equipment Iridium
The current GM Genuine Parts iridium plug — supersedes the older 41-985 that most forum threads still reference, which GM has discontinued.
- Iridium electrode
- GM Original Equipment spec
- Factory-match part from GM itself
- The correct current part number, not a discontinued one
- Slightly pricier than aftermarket iridium options
Bosch Platinum+4 (4417)
Four-ground-electrode platinum design explicitly listed by Bosch as compatible with 1992–2013 Corvettes running LS1/LS2/LS3/LS6 engines.
- Surface air-gap firing
- Four ground electrodes
- Good fouling resistance from the multi-electrode design
- Some LS1 owners on forums report platinum multi-electrode plugs firing less crisply than fine-wire iridium at high RPM
Nology Silver
Nology’s current silver-tip line, offered by the same company as the discontinued Beru Silverstone S1K and marketed by Nology as its modern equivalent for LS1/LS6 owners who liked the Beru’s higher thermal conductivity.
- Silver-alloy center electrode for higher thermal conductivity
- Broader heat range window than standard plugs
- Currently in production, unlike the Beru Silverstone it replaces
- Less forum track record than NGK/Denso/ACDelco on this specific engine
Buying tips
- Heat range, not brand, is the real decision here: stock TR55/TR55IX heat range for unmodified engines, one step colder (TR6) for boosted or high-compression builds.
- The Beru Silverstone S1K, still recommended in older Corvette forum threads, is discontinued in the US — don’t chase it; Nology’s Silver line is the closest current product.
- If you see ACDelco 41-985 referenced online, note that GM has superseded it with the 41-110 — order the current part number.
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