Ignition Systems

The best ignition upgrades for a WRX or STI start with fresh spark plugs — stock heat range for a stock car, one step colder once you are tuned — and move to upgraded coil packs if you get misfires under boost. NGK iridium plugs are the default choice for Subaru’s turbo engines, Mishimoto coil sets are a popular direct replacement when factory coils weaken, and COBB’s one-step-colder plug sets are built for its staged power packages. For most drivers, a quality set of plugs gapped correctly solves rough idle and high-boost stumble.

Ignition parts do one job: light the air-fuel mixture cleanly, every cycle, under boost. Weak links show up as misfire codes, hesitation at wide-open throttle, or a rough cold idle. When shopping, match the heat range to your tune level (colder for more boost), confirm the plug gap for your setup, and make sure coil packs match your exact engine — connectors and dwell characteristics differ between generations.

Brands in This Collection

NGK is the spark plug specialist behind much of the OEM and aftermarket ignition world. Its Laser Iridium and Iridium IX plugs — like the ILKAR8H6 for the 2015–2021 WRX and the heat-range-7 LFR7AIX sets — are the plugs Subaru turbo engines tend to run happiest on, with fine-wire iridium electrodes that hold their gap far longer than copper. Mishimoto, best known for cooling, also builds direct-fit ignition coil sets — including sets for the 2011–2014 WRX / 2011–2021 STI and the 2016–2021 Honda Civic — aimed at owners chasing a stronger, more consistent spark on higher-mileage cars. COBB needs little introduction in the Subaru world: its one-step-colder 2.5L spark plug sets are specced as supporting hardware for tuned EJ engines, the kind of detail that matters once boost goes up.

Start with Performance Spark Plugs, then compare related upgrades in Engine Management Systems. Two proven picks from this collection: NGK [15-21 WRX, 14-16 FXT] Laser Iridium Stock Heat Range and the Mishimoto [11-14 WRX, 11-21 STI] Ignition Coil Set of 4. For engine background, read Subaru EJ257 Engine: Everything You Need To Know.

Frequently Asked Questions

What does spark plug heat range mean?

Heat range describes how quickly the plug sheds heat — a “colder” plug runs cooler at the tip. Tuned and higher-boost engines need colder plugs to avoid pre-ignition; stock cars should stay at the stock heat range. When in doubt, check your year and model listing.

Do I need to gap new spark plugs?

Many iridium plugs come pre-gapped, but you should always verify the gap against your setup — boosted applications often run a tighter gap than stock. Never pry on the fine-wire center electrode; adjust the ground strap only.

Do ignition upgrades require a tune?

Plugs and coils alone do not require a tune, but the reason you are changing heat range usually does: one-step-colder plugs are for cars that are already tuned or about to be. Coils are a maintenance-grade upgrade on any car.

Plugs or coil packs — which do I replace first?

Plugs first: they are wear items and the most common cause of misfires. If fresh, correctly gapped plugs do not fix a high-boost misfire, the coil packs are the next suspect — especially past 60k–80k miles.