Aftermarket Spark Plugs for the 2013-2021 Subaru WRX STI
Keep your STI's turbocharged EJ257 engine firing precisely with the right set of aftermarket spark plugs.
- Stick to top-tier aftermarket brands like NGK or Denso Iridium plugs for reliability and performance.
- For modified STIs, consult a tuner to see if a 'one step colder' spark plug is necessary to prevent engine knock.
- Replacement is a difficult DIY job due to the boxer engine's tight clearances; expect higher shop labor costs than on a typical inline-four engine.
- Change plugs every 60,000 miles for a stock car, or consider a shorter 30,000-mile interval if the car is tuned.
Signs of Failing Spark Plugs in a WRX STI
When your spark plugs start to wear out, your engine's performance will suffer. The signs can be subtle at first but will get worse over time. Ignoring them can lead to more serious engine problems.
- Rough Idle: The engine may shake or vibrate more than usual when the car is stopped.
- Hesitation During Acceleration: When you press the gas, the car might stumble or feel like it's losing power for a moment.
- Reduced Fuel Economy: Worn plugs cause inefficient combustion, making your engine use more fuel than necessary.
- Check Engine Light: A failing spark plug can cause a cylinder to misfire, which will trigger a Check Engine Light. Common codes include P0300 (random misfire) and P0301 through P0304 (misfire in a specific cylinder). 🎬 Watch this guide to help diagnose your engine misfires.
- Difficulty Starting: A weak spark can make it harder for the engine to start, especially when cold.
Choosing the Right Aftermarket Spark Plugs
For the 2013-2021 WRX STI, the factory-installed spark plugs are typically high-quality NGK Iridium units. When choosing an aftermarket replacement, it's important to stick with brands known for their quality and compatibility with high-performance Japanese engines.
OEM vs. Aftermarket Quality
In this case, the Original Equipment Manufacturer (OEM) plugs are made by NGK, a top-tier brand available in the aftermarket. You can often buy the exact same NGK plugs without the Subaru branding for less money. Brands like Denso are also excellent OEM-quality alternatives trusted in many Japanese vehicles. Budget brands like Autolite and Champion are generally not recommended by the STI community for this turbocharged application.
Brand Tiers for the WRX STI
- Top Tier (Highly Recommended): NGK and Denso. These brands are the overwhelming favorites among STI owners and tuners. They offer Iridium plugs that provide long life and consistent performance. NGK Laser Iridium and Denso Iridium plugs are excellent choices.
- Mid-Tier (Use with Caution): Bosch. While a reputable brand for many vehicles, Bosch plugs are less common in the STI community. It's best to stick with the Japanese brands that have a proven track record with the EJ257 engine.
- Budget Tier (Not Recommended): Autolite, Champion. These brands are not suitable for the high-stress environment of a turbocharged STI engine. Using them could lead to poor performance and potential engine issues.
Heat Range is Critical
Spark plugs come in different "heat ranges," which determines how quickly the plug dissipates heat. If you have modified your STI for more power (e.g., increased boost), you will likely need a "colder" spark plug to prevent detonation (engine knock). For example, many tuners recommend a "one step colder" plug for Stage 2 or higher cars. The 2019+ STI even came from the factory with a one-step-colder plug than previous years. Always consult with your tuner about the correct heat range for your specific modifications.
🎬 Learn about choosing the right spark plugs for more power.Known Issues, Recalls, and TSBs
There are no specific recalls or Technical Service Bulletins (TSBs) from Subaru or the NHTSA for spark plug failure, as they are considered a normal wear-and-tear item. However, there was a recall (NHTSA ID: 22V-522) for the back-up lamp switch on 2015-2021 WRX STI models, which is unrelated to engine performance. The most common issues reported by owners are misfires caused by worn plugs or incorrect installation, such as cracking the porcelain insulator.
Aftermarket Spark Plug Cost for 2013-2021 Subaru WRX STI
| Category | Price Range (Set of 4) | Notes |
|---|---|---|
| New Aftermarket (Top Tier) | $40 - $85 | NGK Laser Iridium or Denso Iridium. Price varies by retailer. |
| New OEM | $80 - $120 | Genuine Subaru-branded NGK plugs from a dealership. |
| Shop Labor | $200 - $400 | Labor costs vary by shop and location. The job is more time-consuming than on other cars. |
Frequently Asked Questions (FAQ)
How often should I change the spark plugs on my WRX STI?
Subaru's official maintenance schedule recommends replacement every 60,000 miles. However, many owners and tuners, especially on modified cars, recommend a shorter interval of 30,000 to 40,000 miles to maintain peak performance.
What is the correct spark plug gap?
Most NGK and Denso Iridium plugs for the STI come pre-gapped. The typical gap is around 0.028-0.031 inches for stock heat range plugs. It's always a good idea to verify the gap before installation but be extremely careful, as the iridium tip is fragile and can be damaged by improper gapping tools.
How hard is it to change the spark plugs myself?
It is a challenging DIY job. The boxer engine design places the spark plugs on the sides of the engine with very tight clearance to the frame rails. To access them, you typically need to remove the battery and air pump on one side and the air intake box on the other. Special tools like swivel sockets and various extensions are required.
🎬 See this walkthrough for changing spark plugs on your STI.Can I use cheaper copper spark plugs?
It is not recommended. While copper plugs are cheap, they have a very short service life and are not designed for the high-performance, high-heat environment of the STI's turbocharged engine. Stick with the recommended Iridium plugs for longevity and reliability.
Helpful Videos
Technical Specifications
OEM Part Numbers: 22401AA910
The OEM plug for later models (2018-2021) is the NGK ILFR7H, which is a heat range 7 plug. Earlier models may have used a heat range 6 plug. The plugs are an iridium type with a 14mm thread and 5/8" (16mm) hex size.
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The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- Subaru WRX STI:
- 🎬 Helpful Videos
- 🛍️ Shop This Part
- Signs of Failing Spark Plugs in a WRX STI
- Choosing the Right Aftermarket Spark Plugs
- OEM vs. Aftermarket Quality
- Brand Tiers for the WRX STI
- Heat Range is Critical
- Known Issues, Recalls, and TSBs
- Aftermarket Spark Plug Cost for 2013-2021 Subaru WRX STI
- Frequently Asked Questions (FAQ)
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