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The first thing to get right is that the Trailblazer SS is not a Trailblazer. The 2006–2009 SS carries the LS2 6.0L V8, while every other Trailblazer of that era runs the 4.2L Vortec inline-six — completely different plugs, different heat range, different gap. A great deal of the advice you will find on Trailblazer forums is written for the I6 and will point you at the wrong part. What the LS2 wants is an iridium or platinum fine-wire plug in the correct heat range, gapped at about 0.040 inch, and left alone. This engine is genuinely sensitive to plug variation — it is one of the few modern V8s where owners consistently report misfires and rough idle from a plug that measures fine on paper. Ten options below, with the ones actually validated on the LS2 clearly separated from the ones that need care.
| # | Product | Price | Where to buy |
|---|---|---|---|
| 1 | ACDelco 41-985 Iridium | $8–$16 each | Amazon · eBay |
| 2 | ACDelco 41-110 Iridium | $9–$18 each | Amazon · eBay |
| 3 | NGK TR55IX Iridium IX | $7–$14 each | Amazon · eBay |
| 4 | NGK TR6IX Iridium IX (one step colder) | $8–$15 each | Amazon · eBay |
| 5 | Denso Iridium TT | $10–$20 each | Amazon |
| 6 | Denso ZTJ16R10 (OE-equivalent) | $9–$18 each | Amazon · eBay |
| 7 | ACDelco 41-103 Iridium | $8–$16 each | Amazon · eBay |
| 8 | NGK G-Power Platinum | $5–$10 each | Amazon · eBay |
| 9 | Autolite Iridium XP | $7–$14 each | Amazon · eBay |
| 10 | AC Delco / NGK 8-plug service set | $55–$120 per set of 8 | Amazon · eBay |
The picks, in detail
ACDelco 41-985 Iridium
The factory plug for the LS2 and the safe default. GM specified it, it comes pre-gapped at 0.040 inch, and it is what the engine was calibrated around.
- OE specification for the LS2 6.0L
- Pre-gapped at 0.040 inch (1.01mm) from the factory
- Iridium fine-wire centre electrode
- Manufactured to GM’s Denso-sourced specification
- Long service interval, typically around 100,000 miles
- Zero guesswork — this is the part the engine was developed with
- Pre-gapped correctly, so there is nothing to set and nothing to break
- Cheapest way to guarantee no plug-related driveability complaints
- No performance gain over stock, because it is stock
- Counterfeits circulate; buy from a reputable supplier
- Not the right heat range if the engine is heavily modified
ACDelco 41-110 Iridium
The current-generation ACDelco iridium that supersedes several earlier LS part numbers. The straightforward choice when 41-985 stock is thin.
- ACDelco Professional iridium
- Supersedes several earlier LS-family numbers
- Pre-gapped from the factory
- Iridium centre with platinum ground pad
- Extended service life
- Widely available where older numbers have been discontinued
- Same OE-grade construction and reliability
- Pre-gapped, so no setting required
- Verify supersession against your specific VIN before ordering
- Marginally more expensive than 41-985
- No performance benefit over the factory plug
NGK TR55IX Iridium IX
The most popular aftermarket alternative in the LS community and the one with the deepest real-world track record on this engine family.
- NGK stock number 7164
- Iridium IX fine-wire construction, 0.6mm centre electrode
- Same heat range as the TR5 series
- Tapered ground electrode for better flame propagation
- Supplied gapped, commonly around 0.032–0.035 inch
- Enormous LS-community track record — thousands of documented installs
- The fine 0.6mm electrode lights the mixture with less voltage demand
- Usually cheaper than the ACDelco iridium
- Often ships gapped tighter than the LS2 spec, so it needs checking
- TR5 and TR55 are the same plug at different gaps — easy to confuse when ordering
- Adjusting a fine-wire plug is risky; see the tips below
NGK TR6IX Iridium IX (one step colder)
The forced-induction answer. If the SS has a supercharger or turbo, a colder plug is not optional — it is what stops detonation from a plug tip that stays too hot.
- One heat range colder than the TR5/TR55
- Iridium IX fine-wire construction
- Standard choice for boosted LS builds
- Same thread and reach as the stock plug
- Commonly gapped down for boost
- The correct plug for a boosted or nitrous LS2, where a stock-heat plug is a real engine risk
- Well proven across the boosted LS community
- Inexpensive insurance against detonation damage
- Wrong for a stock engine — a colder plug on a naturally aspirated LS2 can foul at low speed
- Boosted applications usually need the gap closed further, often to 0.030 inch or less
- Shorter service life than the OE plug
Denso Iridium TT
Denso builds the factory plug for this engine under GM’s part number, so their own branded line is the same manufacturer with a twin-tip design that improves ignitability.
- Twin-tip design: 0.4mm iridium centre and platinum ground
- Denso is the OE manufacturer for the GM iridium plugs
- Long service interval
- Pre-gapped
- Available in the correct LS2 heat range
- Same manufacturer as the factory plug, with a genuinely finer centre electrode
- The twin-tip design measurably reduces required firing voltage
- Good cold-start behaviour
- More expensive than the NGK equivalent
- You must confirm the correct application number — Denso’s LS range spans several heat grades
- Little practical difference from stock on an unmodified engine
Denso ZTJ16R10 (OE-equivalent)
The actual Denso part behind the factory LS2 plug. Useful to know because it lets you cross-reference and avoid the common mistake of fitting the colder Z06 plug.
- The Denso part corresponding to the stock LS2 plug
- One heat range hotter than the Corvette Z06 plug (ZTJ20R10)
- Iridium construction
- Pre-gapped to GM specification
- OE-equivalent fitment
- Exactly the factory plug, sometimes cheaper under the Denso number than the ACDelco one
- Knowing this cross-reference prevents the Z06-plug mistake
- Identical performance to OE because it is OE
- Confusing to source; not every retailer lists the raw Denso number
- No upgrade over the ACDelco part — it is the same plug
- Easily confused with ZTJ20R10, which is a different heat range
ACDelco 41-103 Iridium
A widely recommended ACDelco iridium across GM V8 applications. Worth knowing, but check it against your engine rather than assuming it is interchangeable.
- ACDelco iridium, factory gapped around 0.043 inch
- Common across several GM applications
- Iridium fine-wire centre electrode
- Long service interval
- Frequently cited on GM truck forums
- Easy to find and well-supported by ACDelco’s distribution
- Reliable OE-grade construction
- Consistent quality
- Its factory gap is set for a different application than the LS2’s 0.040 inch
- Frequently recommended on Trailblazer forums by people running the 4.2L I6, not the SS
- Verify heat range and reach against your VIN before ordering
NGK G-Power Platinum
The budget fine-wire option. Platinum rather than iridium, so a shorter life, but the same fine-electrode benefit at a noticeably lower price.
- Platinum fine-wire centre electrode
- Correct heat range available for the LS2
- Roughly half the service life of an iridium plug
- Trivalent metal plating for anti-seize and corrosion resistance
- Pre-gapped
- Cheapest credible option for eight plugs at once
- Fine-wire construction still fires more reliably than a copper plug
- Sensible if you change plugs often anyway for diagnostic reasons
- Shorter interval means you will do this job twice as often on an engine where access is awkward
- Not the OE material specification
- False economy over the life of the vehicle
Autolite Iridium XP
A well-regarded alternative brand with a heavy-duty iridium design, worth considering if ACDelco and NGK are both out of stock.
- Iridium-enhanced fine-wire centre electrode
- Platinum-backed ground electrode
- Correct heat range available for LS applications
- Pre-gapped
- Competitive pricing
- Solid third alternative when the mainstream options are unavailable
- Priced between the platinum and premium iridium options
- Good cold-weather starting reputation
- Much less LS-specific community data than NGK or ACDelco
- The LS2 is documented as sensitive to plug variation, which argues for the proven choices
- Verify the application number carefully
AC Delco / NGK 8-plug service set
Buy all eight together. Mixed brands or mixed ages across cylinders is a genuine cause of the rough idle people then chase with a scan tool.
- Complete set of eight matched plugs
- Same production batch and identical gap
- Available in both ACDelco and NGK part numbers
- Often bundled with wires or boots
- Cheaper per plug than buying singles
- Matched plugs across all eight cylinders is the correct way to service this engine
- Cheaper per unit than individual purchases
- Removes the temptation to replace only the cylinder that misfired
- Bundled wire sets are often lower quality than buying wires separately
- More expensive up front than one plug
- Check the bundle is the right heat range, not a generic LS fitment
Buying tips
- Confirm you have the LS2, not the 4.2L inline-six. This is the single most important check on this page. The Trailblazer SS (2006–2009) has the 6.0L LS2 V8; every other Trailblazer of that generation has the 4.2L Vortec I6. Most forum threads titled ‘best spark plugs for Trailblazer’ are about the I6 and the parts do not cross over.
- Do not re-gap iridium or platinum plugs. This is the second-most-common way to ruin a good plug. Fine-wire electrodes are fragile, and the standard gapping tool will chip the iridium tip or bend the ground strap off-centre. Modern iridium plugs come gapped from the factory. Buy the correct part number and fit it as it comes out of the box.
- The LS2 spec is about 0.040 inch, and the plug should already be there. ACDelco iridium plugs for this engine ship at 0.040. If you must check, use a wire-loop gauge rather than a coin-style tool, and only verify — do not adjust.
- Torque them properly and do not use anti-seize on plated plugs. Aluminium heads are unforgiving of over-torquing and the LS2’s plugs thread straight into the head. Most modern plugs have plating that already acts as an anti-seize; adding compound reduces friction and causes over-torquing at the same wrench setting, which is how threads get pulled. Use a torque wrench to the manufacturer’s figure.
- Change all eight at once. Plugs wear together, and a single new plug among seven worn ones creates an ignition imbalance that the ECU will try to compensate for. It is also a miserable job to do twice.
- Inspect the coil boots while the plugs are out. On an engine this age the boots harden, crack and arc to the head, which produces exactly the misfire people blame on plugs. If a boot is stiff or shows a grey tracking line inside, replace it — a new plug in a failed boot fixes nothing.
- Go one heat range colder only if you have added boost. A supercharged or turbocharged LS2 needs the colder TR6IX and usually a tighter gap, often 0.030 inch or less, because a bigger gap under boost demands more voltage than the coil can supply and causes spark blowout. On a stock engine a colder plug will foul.
- Read the old plugs before you bin them. A light tan tip is correct. Black and sooty means it is running rich or the plug is too cold; white and blistered means lean or too hot; oil on the threads points at valve stem seals. Eight plugs laid out in cylinder order is the cheapest diagnostic tool you own.
As an Amazon Associate and eBay Partner, toptenpick.com earns from qualifying purchases. Prices and availability are subject to change.