We researched and compared the top spark plugs for LS engines based on manufacturer specifications, industry standards, and aggregated owner feedback. Our evaluation covers heat range, electrode material, gap retention, and real-world performance across LS1, LS2, LS3, LS6, and LS7 builds. Whether you need a daily driver plug or a race-ready option, this guide helps you choose the right one.
| Photo | Product | Score | Buy |
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NGK TR55IX Iridium IX Best Overall for Daily Drivers Iridium tip, 0.044 in. gap, heat range 5, 14mm thread |
9.1 | 🛒 Check Price |
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ACDelco 41-962 Iridium OEM Replacement for LS2/LS3 Iridium tip, 0.040 in. gap, heat range 6, 14mm thread |
8.7 | 🛒 Check Price |
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Denso 5343 Iridium TT Longest Life Iridium Plug Iridium twin-tip, 0.044 in. gap, heat range 5, 14mm thread |
8.4 | 🛒 Check Price |
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NGK TR6 Iridium IX Best for Forced Induction Iridium tip, 0.035 in. gap, heat range 6, 14mm thread |
9.0 | 🛒 Check Price |
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ACDelco 41-110 Iridium OEM for LS1/LS6 Iridium tip, 0.060 in. gap, heat range 5, 14mm thread |
8.1 | 🛒 Check Price |
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NGK 6510 LTR6IX-11 Iridium Best for LS3/LS7 with High Compression Iridium tip, 0.044 in. gap, heat range 6, 14mm thread, resistor type |
8.8 | 🛒 Check Price |
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Autolite XP5683 Iridium Budget Iridium Option Iridium tip, 0.044 in. gap, heat range 5, 14mm thread |
7.8 | 🛒 Check Price |
1. NGK TR55IX Iridium IX: Best Overall for Daily Drivers
The NGK TR55IX Iridium IX is a top choice for stock and lightly modified LS engines. We researched owner feedback across forums and found it delivers reliable cold starts and smooth idle. Its iridium tip resists wear, and the pre-gapped design saves installation time. However, it is not recommended for forced induction or nitrous builds where a colder heat range is needed.
If you have a daily driver LS1, LS2, or LS3 with bolt-ons, this plug offers a great balance of performance and longevity. Skip it if you are running high boost or race fuel; consider a colder plug like the NGK TR6.
- Iridium center electrode for long life and consistent spark
- Pre-gapped to 0.044 in. for most LS applications
- Heat range 5 suitable for stock to mildly modified engines
Pros: Excellent value for daily driven LS engines; Long service interval, typically over 60,000 miles
Cons: Not ideal for high-boost or nitrous applications
2. ACDelco 41-962 Iridium: OEM Replacement for LS2/LS3
The ACDelco 41-962 is the OEM plug for many LS engines, including the LS2 and LS3. We compared its specifications to GM service manuals and confirmed it meets exact heat range and gap requirements. Owner reviews highlight its trouble-free performance and long life. However, it is more expensive than iridium plugs from NGK or Denso.
Choose this plug if you want a direct OEM replacement and are willing to pay a bit more. Skip it if you are on a tight budget or need a colder plug for a supercharged build.
- Factory original equipment for many GM LS engines
- Iridium construction for up to 100,000 mile service life
- Pre-set gap ensures proper installation out of the box
Pros: Perfect fit for LS2 and LS3 engines; Trusted OEM quality and reliability
Cons: Premium price compared to copper plugs
3. Denso 5343 Iridium TT: Longest Life Iridium Plug
The Denso 5343 Iridium TT features a unique twin-tip design that requires lower firing voltage, which can extend coil life. We reviewed technical data showing its wear resistance is among the best. However, owner feedback indicates it may not be as performance-oriented in high-output builds compared to NGK options.
Ideal for daily drivers who want maximum service interval and don’t mind the premium price. Not the best choice for high-horsepower or forced induction setups where a colder heat range is required.
- Twin-tip iridium design for reduced voltage requirement
- Long life, rated for over 100,000 miles
- Pre-gapped and ready to install
Pros: Exceptional durability and longevity; Smooth idle and improved fuel efficiency
Cons: Higher cost than single-tip iridium plugs
4. NGK TR6 Iridium IX: Best for Forced Induction
The NGK TR6 is the go-to plug for boosted LS engines. We researched build threads and dyno results from the LS community, and it is consistently recommended for engines with superchargers, turbos, or nitrous. The colder heat range helps prevent pre-ignition. However, it may foul faster in a daily driver that sees little high-load operation.
This plug is perfect for modified LS engines making over 500 hp. Skip it if your LS is stock or mostly driven gently; the TR55IX will serve you better.
- Colder heat range (6) for boosted or nitrous applications
- Iridium tip resists fouling and pre-ignition
- Commonly gapped to 0.035 in. for forced induction
Pros: Excellent for supercharged and turbo LS engines; Reliable spark under high cylinder pressure
Cons: Shorter service life in daily driving due to colder range
5. ACDelco 41-110 Iridium: OEM for LS1/LS6
The ACDelco 41-110 is the OEM spark plug for LS1 and LS6 engines. We verified its 0.060 in. gap against GM specifications. It provides a smooth idle and reliable performance in stock applications. However, its wide gap is not suitable for forced induction, and some owners report misfire when adding boost.
Best for stock or lightly modified LS1/LS6 cars. Avoid if you plan to supercharge or turbocharge; switch to a plug with a tighter gap and colder heat range.
- Factory original for 1997-2004 LS1 and LS6 engines
- Wide 0.060 in. gap for improved idle quality
- Iridium center electrode for long life
Pros: Direct OEM replacement for early LS engines; Smooth idle and good fuel economy
Cons: Wide gap may cause misfire under high boost
6. NGK 6510 LTR6IX-11 Iridium: Best for LS3/LS7 with High Compression
The NGK 6510 LTR6IX-11 is designed for LS engines with higher compression ratios, such as the LS3 and LS7. We compared its heat range to other NGK plugs and found it offers a good balance for naturally aspirated performance builds. Owner feedback praises its consistent spark and resistance to fouling. However, it costs a bit more than standard NGK iridium plugs.
Ideal for high-compression naturally aspirated LS engines. Not necessary for stock LS1 or LS2; those engines are fine with TR55IX.
- Heat range 6 for high-compression LS3 and LS7 engines
- Resistor type reduces radio frequency interference
- Pre-gapped to 0.044 in. for easy installation
Pros: Optimized for high-compression LS builds; Reduces misfire risk in high-performance applications
Cons: More expensive than standard TR6 plugs
7. Autolite XP5683 Iridium: Budget Iridium Option
The Autolite XP5683 offers an iridium spark plug at a lower cost than major competitors. We examined owner reviews and found mixed experiences: some report satisfactory performance, while others note premature wear or misfire. The value is appealing for budget builds, but durability may not match NGK or Denso.
Consider this plug if you need an iridium plug on a tight budget for a stock LS engine. Skip it if you demand maximum reliability and long service life; invest in a premium brand instead.
- Iridium tip at a lower price point
- Pre-gapped for most LS applications
- Heat range 5 suitable for stock engines
Pros: Affordable iridium option; Decent performance for daily driving
Cons: Less consistent quality control per owner reports; Shorter lifespan than NGK or Denso iridium plugs
Frequently Asked Questions
What is the best spark plug for a stock LS1 engine?
For a stock LS1, the ACDelco 41-110 Iridium or NGK TR55IX are excellent choices. Both match the factory heat range and gap specifications. The ACDelco is OEM, while the NGK offers comparable performance at a lower price.
Can I use NGK TR6 plugs in a naturally aspirated LS engine?
Yes, but they are colder than necessary. The TR6 (heat range 6) is designed for forced induction or high-compression builds. In a naturally aspirated engine, they may foul sooner and cause rough idle. Stick to heat range 5 for stock or mildly modified LS engines.
How often should I change spark plugs on an LS engine?
Iridium plugs typically last 60,000 to 100,000 miles depending on driving conditions. Copper plugs need replacement every 30,000 miles. Always follow the manufacturer’s recommended interval in your owner’s manual.
What gap should I set for my LS spark plugs?
Stock LS engines usually require 0.040 to 0.060 inches depending on the specific engine. For boosted engines, a tighter gap of 0.035 inches is common to prevent misfire. Always check the plug manufacturer’s recommendation and your engine specs.
Are iridium spark plugs worth the extra cost for LS engines?
Yes, for most drivers. Iridium plugs offer longer life, better ignitability, and improved resistance to wear. They are especially beneficial in high-performance or forced induction LS builds. Copper plugs are cheaper but require more frequent changes.
Our Verdict
After researching and comparing specifications, owner feedback, and industry standards, our top pick is the NGK TR55IX Iridium IX for its outstanding balance of performance, durability, and value in daily-driven LS engines. The runner-up is the NGK TR6 Iridium IX, which is the best choice for forced induction and high-horsepower builds.
Last reviewed and spec-checked: May 12, 2026. We re-check our picks and listings periodically.
