The EJ20 and EJ25 powered every WRX from 2002-2014 and every STI all the way through 2021, before Subaru finally moved the WRX over to the FA20DIT in 2015. Three engine codes, two plug families, and a lot of listings out there with the wrong part number written into the mod notes. Here’s the correct stock and one-step-colder NGK plug for each EJ code, plus the gap. Working on a 2015+ WRX with the FA20DIT instead? Our FA20DIT spark plug guide covers that one. Mid-build on an EJ car? Our EJ-series mods guide covers the rest of the staged upgrade path.
WRX & STI Spark Plugs by Engine Code
Two plug families cover all three EJ engine codes: BKR-series for the 2002-2005 WRX’s EJ205, and LFR-series for the EJ255 (2006-2014 WRX) and EJ257 (STI, 2004-2021). Get the family right first, then pick stock heat or one-step-colder depending on what the car’s actually making.
2002-2005 WRX (EJ205) use the factory NGK PFR6G (Subaru P/N 22401AA530), with an iridium equivalent in the NGK BKR6EIX-11. Stock-to-mild builds should stick with that stock heat range; once you’re past stock power, step up to the NGK BKR7EIX-11, one step colder heat range 7 NGK plugs. There’s also a BKR8EIX which are two-steps-colder option for cars running HIGH boost and making big power.
2006-2014 WRX (EJ255) and 2004-2018 STI (EJ257) both feature the EJ25 engine and run the factory OEM NGK ILFR6B spark plug (Subaru P/N 22401AA630), the iridium equivalent being NGK LFR6AIX-11. However Subaru changed course using 1 step colder (heat range 7 plugs) starting with the STI Type RA 2018-2021 STI, NGK LFR7AIX is the OEM replacement and exactly the plug we recommend for ALL EJ25 STI’s RA or standard STI’s alike. All NGK STI spark plugs are in stock and shipping out daily. Please note we ONLY sell genuine NGK parts always purchased through NGK’s authorized channels to avoid wasting time and money on copy/knock off NGK plugs found on marketplace listings like Ebay and Amazon.
Worth double-checking whatever’s written into a listing’s mod notes before you assume it’s accurate — we’ve seen “one step colder” attached to what’s actually just the stock-heat plug, part number and all, more than once. A mod list that just says “iridium plugs” with no part number doesn’t actually tell you what’s installed.
WRX & STI Spark Plug Gap & When to Go Colder
Factory gap on all three EJ codes is commonly specified in the 0.028″-0.031″ range — check it against a factory service manual for your specific model year before you set it, since we’ve seen slightly different figures floating around depending on the source. Use a wire-type gap tool rather than a flat feeler gauge on the iridium center electrode; it’s thin and bends easily if you’re not careful.
For the STI, our take is simple: any EJ257 running mods or an increase in boost, even mild ones, gets the one-step-colder LFR7AIX — we don’t wait for a specific power number to make that call. Subaru landed on the same answer from the factory: every 2019-2021 STI, and the 2018 Type RA before it, shipped one step colder than earlier STI years. For the WRX’s EJ255, the same plug is the move once a build’s making more than stock power. Iridium matters here for more than longevity: the finer center electrode fires a more concentrated spark, which helps ignition stay consistent as cylinder pressures climb under boost. Spark blowout under load on the colder plug, even with good boost control, usually points to a weak ignition coil rather than the wrong plug — worth swapping in a stronger coil at the same time.
Frequently Asked Questions
What spark plug does a WRX or STI use stock?
Depends on the engine code, not the model year — that’s the whole reason this guide exists. 2002-2005 WRX (EJ205) runs a BKR-series plug, 2006-2014 WRX (EJ255) and 2004-2021 STI (EJ257) run the LFR-series. There’s no single “WRX spark plug,” which is exactly the mix-up we see written into a lot of mod lists.
Do aftermarket iridium plugs actually make a difference over stock?
On a bone stock EJ, honestly not much you’d feel day to day — stock heat range iridium is already a solid plug. Where it matters is once you’re modified: a colder heat range and the finer iridium tip both help ignition stay consistent as cylinder pressures climb under boost.
How hard is it to DIY a spark plug swap on an EJ?
Doable in an afternoon with basic tools, though EJ engine bays are tight enough that pulling the intake or a coil pack bracket out of the way makes the rear-bank plugs a lot easier to reach. Budget more time than you think you’ll need the first time through.
What kills EJ spark plugs early?
Usually one of two things: running the wrong heat range for the power level, or carbon fouling from oil intrusion on a car that’s overdue for valve cover gaskets. Neither shows up as a dramatic failure — more often it’s a rough idle or an intermittent misfire under boost that gets blamed on the tune before anyone pulls a plug to look.
We keep all four of these part numbers in stock and ship same day. Browse what’s currently listed if you want to see real EJ-powered builds: EJ257-coded STI listings and EJ255-coded WRX listings on get.ffrides.com.