Denso

The best Denso spark plugs for most owners are the stock-heat-range options that match their exact engine, with one-step-colder Iridium Power plugs reserved for the modified turbo applications listed here. This Denso collection at JDMuscle covers Iridium Power, Platinum TT, and U-Groove plugs for Subaru WRX and WRX STI and for Mazdaspeed3 and Mazdaspeed6, plus a Denso 280 lph universal fuel pump. Check your year and model and the heat range in the product title before ordering, because the same car can use different plugs by generation.

A spark plug must deliver a consistent spark under pressure, heat, and boost. Heat range is the key choice here. Stock heat range suits a stock or lightly modified car, one step colder is the common direction for tuned turbo cars listed here, and two steps colder is a more specific choice that should follow your tuner or build plan rather than guesswork.

Electrode type is the second choice. Iridium Power plugs are the performance line here, the 4506 PKH20TT is a single platinum option for 2006-2014 WRX and 2004 and later WRX STI as listed, and U-Groove plugs are the traditional design at stock heat range for the same applications.

Denso is a major original-equipment ignition supplier, and that OE background is the core of its reputation: plugs specified by engine application, with clear part numbers such as ITV20 and ITV22 for Mazdaspeed cars and IK22, IKH22, and IKH24 for Subaru applications in this collection. In Iridium Power form, Denso focuses on a fine iridium electrode for a strong, repeatable spark in turbo engines, which is why its colder options appear so often in WRX, WRX STI, and Mazdaspeed listings.

NGK is the other brand most Subaru and Mazdaspeed owners compare against Denso, with its own iridium lines and heat-range steps for the same cars. Comparing Denso and NGK by exact application and heat range, rather than by brand preference alone, is the sensible way to shop; you can browse both alongside the wider performance spark plugs and ignition systems ranges.

The Denso fuel pump here, listed as a 280 lph universal part, is a reminder to treat fuel delivery and ignition together on a modified car, so review the fuel system range alongside plugs, and see our guide to Subaru engine modifications.

Should I run one step colder plugs?

Only when your setup calls for it. The colder Denso options here are listed for specific WRX, WRX STI, and Mazdaspeed applications; if your car is stock, start with the stock-heat-range listing and check with your tuner if you are unsure.

How do I know which Denso plug fits my car?

Match the product title to your year and model first, then confirm the part number and heat range, such as IKH22 for 2006-2014 WRX and 2004 and later WRX STI as listed. Do not assume a plug for 2002-2005 WRX fits later cars.

Do spark plugs need to be gapped?

Many modern iridium plugs arrive pre-gapped, but verify the gap against your engine specification before install and handle the fine electrode carefully.

When should spark plugs be replaced?

Replace them at your manufacturer service interval, sooner if you have misfires or rough idle. Worn plugs can mimic more serious problems, so they are a sensible early check.