Denso SK20HR11 Iridium Platinum Spark Plugs — 4-Pack (3421) for 4-Cylinder Engines, Long-Life Performance

These are genuine DENSO SK20HR11 (3421) iridium platinum spark plugs sold as a brand-new four-pack engineered for reliable ignition and long service life.

Built to DENSO's factory specifications, the SK20HR11 combines an iridium center electrode with a platinum-enhanced ground electrode for consistent spark delivery, reduced wear, and stable combustion across a wide range of engines. The four-pack format gives you a complete cylinder set for most 4-cylinder applications, packaged and shipped from the USA with free delivery to U.S. states and territories.

How do these spark plugs improve engine performance?

Iridium and platinum materials allow a smaller, more precise center electrode that creates a stronger, more focused spark. That promotes more complete fuel burn and steadier ignition timing without increasing voltage demands on the ignition system.

• Iridium center electrode for focused spark and durability
• Platinum-enhanced ground electrode to resist erosion
• Consistent gap and heat range matched to OEM specs
• Sold as a 4-piece set to replace all cylinders at once

Are these DENSO plugs compatible with my vehicle?

The SK20HR11 is a specific part number (DENSO 3421) designed for vehicles that call for that heat range, thread size, and electrode configuration. Always confirm compatibility by checking your vehicle's service manual or existing plug part numbers before purchase.

• Part number: DENSO 3421 (SK20HR11)
• Sold in packs of four for complete 4-cylinder replacements
• Fits models that list SK20HR11/3421 in OEM cross-reference
• Verify thread pitch and reach to avoid fitment issues

What should I expect during installation and service life?

Installation follows standard spark plug procedures: correct torque, proper gap (pre-set by the manufacturer), and anti-seize considerations as recommended by DENSO. Iridium and platinum plugs typically last longer than copper plugs, offering extended intervals between replacement when installed correctly.

• Pre-set gap per DENSO specification; re-check if required
• Tighten to vehicle manufacturer torque settings—do not overtighten
• Longer replacement intervals than conventional plugs under normal conditions
• Inspect wires/coils and ignition components when replacing plugs

What does the purchase include and how is it shipped?

This listing provides four brand-new, genuine DENSO SK20HR11 (3421) spark plugs in original packaging. The item ships with free delivery within the United States and U.S. territories so you receive a full set ready for installation.

• One order = four DENSO SK20HR11 (part 3421) spark plugs
• New, genuine DENSO parts in manufacturer packaging
• Free shipping to U.S. states and territories for this item
• Ideal for replacing all cylinders on compatible engines

Who is this for? Mechanics, DIY enthusiasts, and vehicle owners seeking a direct-fit replacement with long-lasting iridium/platinum electrodes will find this DENSO four-pack suitable. It’s particularly useful for anyone replacing an entire bank of cylinders at once or upgrading from standard plugs to a more durable material without changing their ignition components. Always cross-check the SK20HR11 (3421) designation with your vehicle’s recommended parts list to ensure proper fitment before ordering.