NGK Ruthenium HX Spark Plugs for K20C1/K20C4/K20C9 Engines

NGK Ruthenium HX Spark Plugs - K20C/L15B Turbo Motors (Set of 4)

You're on your way to work and your Civic Si or Type R starts stumbling at 3,000 RPM when you roll into the throttle. Or maybe you're getting rough idle at stoplights and the car feels like it's missing. Your stock spark plugs are wearing out. The center electrode's eroded, the gap's opened up, and now your ignition system can't fire the plug consistently under boost. We've seen it a thousand times. Stock plugs last 60,000-80,000 miles if you're lucky, then they start falling off. NGK Ruthenium HX plugs are what you replace them with. These aren't your basic copper plugs. The center electrode's made from ruthenium with a 0.4mm fine wire design that fires with way less voltage than copper or standard iridium. That means cleaner combustion, smoother throttle response, and no more stumbles when you're getting on it. If you're running a stock turbo or mild bolt-ons on your Civic Si, Type R, Integra, Accord 2.0T, TLX, or RDX, these are the plugs you want.

Here's What Happens When Your Plugs Wear Out

Your K20C or L15B motor's a turbocharged direct injection motor. That combination beats the hell out of spark plugs. Direct injection means the fuel's being sprayed into the combustion chamber at 2,000+ PSI. The turbocharger means you're running 15-20 PSI of boost. Every time the plug fires, it's creating an arc across the gap in a high-pressure, high-temperature environment. That arc erodes the center electrode. After 60,000-80,000 miles, the electrode's worn down enough that the gap's opened from 0.031 inch to 0.040 or 0.045 inch. A wider gap needs more voltage to fire. Eventually your ignition coils can't generate enough voltage to jump the gap consistently, especially when you're under boost and cylinder pressures are sky-high. That's when you get misfires. The car stumbles when you're accelerating. Idle gets rough. Sometimes you'll get a flashing check engine light if the misfire's bad enough. Replace the plugs and all of that goes away.

Why Ruthenium and Platinum Matter

NGK builds these plugs with a 0.4mm ruthenium center electrode and a 0.8mm platinum ground electrode. Ruthenium's one of the hardest, most wear-resistant metals you can use for a spark plug electrode. It's way more expensive than copper or iridium but it lasts longer and it erodes way slower. The 0.4mm fine wire diameter means the electrode needs less voltage to create a spark compared to a thicker electrode. Your ignition coils aren't working as hard and the spark's more consistent across the entire RPM range. The platinum ground electrode's just as wear-resistant as the ruthenium center electrode. Cheap plugs use a nickel alloy ground electrode that erodes fast. Platinum doesn't. You're getting 100,000+ miles out of these plugs if you're driving normally. If you're tracking the car or running more boost, you'll still get way more life than stock plugs.

They Don't Seize in the Head

NGK coats the threads with trivalent metal plating. If you've ever pulled spark plugs out of a Honda motor that's got 100,000 miles on it, you know the threads can seize in the aluminum head. Sometimes you're fighting with a breaker bar trying to get the plug to turn. Sometimes the plug breaks and you're drilling it out. The trivalent plating prevents that. It's an anti-corrosion, anti-seize coating that keeps the threads from bonding to the aluminum. When you pull these plugs out in 60,000 or 80,000 miles, they're going to turn smooth and come out clean. No drama, no broken plugs, no stripped threads.

Heat Range 8 Is Right for Most Builds

The heat range on these plugs is 8. That's correct for stock K20C and L15B motors and it's also fine if you're running mild mods like an intake, exhaust, and a tune. Heat range determines how fast the plug dissipates heat from the tip. Too cold of a plug and it'll foul from carbon buildup. Too hot of a plug and you'll get pre-ignition or detonation. Heat range 8 keeps the plug at the right operating temperature for stock boost levels and stock or mildly modified power levels. If you've got a bigger turbo and you're making 400+ whp or you're running E85 and serious boost, you'll probably need to step down to a colder plug like a heat range 7 or 6. Talk to your tuner. For everyone else running a stock turbo or bolt-ons, heat range 8's right.

Pre-Gapped and Ready to Go

These plugs come pre-gapped at 0.031 inch from NGK. That's the factory spec for K20C and L15B motors. You don't need to gap them. Don't gap them. Just pull your old plugs out, screw these in, torque them to 13 lb-ft (that's the Honda spec for these motors), and you're done. If you over-torque them, you'll crack the ceramic insulator and the plug's trash. Use a torque wrench. Don't guess. NGK rates these plugs for 120,000 miles but that's under ideal conditions with normal driving. If you're tracking your car, check the plugs every 20,000-30,000 miles. Pull them out, look at the electrode wear, look at the color of the insulator tip. That'll tell you if the plugs are wearing normally or if your tune's off.

What You Get

• Set of 4 NGK Ruthenium HX spark plugs
• NGK part number: LKAR8BHX
• NGK stock number: 91784
• Replaces OEM part: 12290-59B-003
• 0.4mm ruthenium fine wire center electrode
• 0.8mm platinum projected square ground electrode
• Trivalent metal plating for anti-corrosion and anti-seize
• Alumina silicate ceramic insulator with copper core
• Heat range 8 (correct for stock and lightly modified K20C and L15B motors)
• Pre-gapped at 0.031 inch (0.8mm)
• Rated for 120,000 miles under normal driving conditions

Fits Your Car

• 2017-2021 Honda Civic Si
• 2022-2026 Honda Civic Si
• 2017-2021 Honda Civic Type R
• 2023-2026 Honda Civic Type R
• 2023-2026 Acura Integra A-Spec
• 2024-2026 Acura Integra Type S
• 2021-2026 Acura TLX 2.0T
• 2019-2026 Acura RDX
• 2018-2022 Honda Accord 2.0T

Note: Heat range 8 is correct for stock and mildly modified motors. If you're running a bigger turbo, E85, or making 400+ whp, talk to your tuner about stepping down to a colder plug. Don't gap these plugs - they come pre-gapped at 0.031 inch from the factory. Torque them to 13 lb-ft when you install them. Over-torque and you'll crack the ceramic insulator. If you're tracking your car or running more boost, check the plugs every 20,000-30,000 miles and look at the electrode wear and insulator color.