NGK Racing Spark Plug Box of 4 (R2556G-9) - 93253

The NGK R2556G-9 Racing Spark Plug (part #93253) is a competition-grade ignition component engineered by NGK specifically to withstand the harshest engine conditions a high-performance or racing application can throw at it. Sold here as a box of 4, these plugs combine a fine wire iridium center electrode with a platinum-tipped ground electrode — a pairing that delivers superior ignitability, long-lasting durability, and strong anti-fouling performance where a standard plug simply won't cut it.

Key Features & Benefits

• Fine Wire Iridium Center Electrode (0.6 mm): The ultra-small 0.6 mm iridium tip concentrates the spark energy for a more focused, reliable ignition event — critical when you need consistent combustion under high-load racing conditions.
• Platinum-Tipped Ground Electrode: Platinum on the ground electrode resists erosion far longer than standard nickel, preserving gap geometry and ignitability over extended use — even in demanding environments.
• Recessed Fine Wire Projection: The recessed electrode design positions the firing tip to optimize flame kernel development inside the combustion chamber, supporting improved throttle response.
• Special Insulator Nose Configuration: Engineered specifically to improve throttle response — a tangible on-track benefit when rapid load transitions matter.
• Pure Alumina Silicate Ceramic Insulator: Provides superior mechanical strength and efficient heat transfer, helping the plug manage thermal stress under sustained high-RPM use.
• Copper Core: Aids in heat removal from the center electrode, helping maintain the plug within its optimal operating temperature range and reducing the risk of pre-ignition.
• Triple Seals: Three seals prevent combustion gas leakage past the plug body, maintaining cylinder pressure integrity.
• Corrugated Ribs on Insulator: Prevent flashover — the unwanted electrical discharge along the insulator surface that can cause misfires, especially in high-voltage racing ignition systems.
• 5k Ohm Resistor: Built-in resistor suppresses electromagnetic interference (EMI), protecting sensitive electronics and data acquisition systems common in motorsport environments.
• Heat Range 9: A specific heat range designation engineered for high-output, high-temperature applications — choose this plug when your engine's tune and operating conditions demand it.

Specifications

• NGK Part Number: 93253
• NGK Stock Number: R2556G-9
• Thread Diameter: 12 mm
• Thread Pitch: 1.25 mm
• Seat Type: Gasket
• Reach: 26.5 mm (1.04")
• Hex Size: 5/8" (16 mm)
• Terminal Type: Solid
• Gap: 0.028" (0.7 mm)
• Center Electrode Material: Iridium — Fine Wire, 0.6 mm
• Ground Electrode Material: Platinum — Slant type
• Projection: Recessed
• Resistor: Yes — 5k Ohm
• Heat Range: 9
• Insulator: Pure Alumina Silicate Ceramic
• Torque Spec (Cast Iron Head): 10.8–18 lb-ft
• Torque Spec (Aluminum Head): 10.8–14.5 lb-ft
• Quantity per Box: 4 plugs

Fitment

The NGK R2556G-9 (93253) is a racing-specific spark plug and is not cross-referenced to a standard OEM automotive or powersports application in NGK's published fitment database. These plugs are selected based on technical specifications — thread diameter (12 mm), thread pitch (1.25 mm), reach (26.5 mm), heat range (9), and gap (0.028") — rather than a year/make/model lookup. They are intended for purpose-built racing engines, heavily modified street engines, or any application where a builder or tuner has determined that the R2556G-9's specific heat range, electrode geometry, and construction are the correct match for their combination.

Always verify fitment with your engine builder, tuner, or NGK technical support before ordering racing plugs. If you need help matching these plugs to your engine, contact the ThreePiece.us team directly — we're here to help.

What's in the Box

• 4 × NGK R2556G-9 Racing Spark Plugs (NGK part #93253)

Why Buy from ThreePiece.us

• Free Shipping: Every order ships free — no minimum, no surprises at checkout.
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• Expert Fitment Support: Not sure if this is the right plug for your build? Our team has served 10,000+ customers and can help you verify compatibility before you buy. Reach us at 813-535-5801 or via our contact page.
• Genuine NGK Products: We carry 100% authentic NGK parts — no counterfeits, no substitutions.

Frequently Asked Questions

Q: What is included in this listing?
A: You receive a box of 4 NGK R2556G-9 racing spark plugs (NGK part number 93253). Each plug is an individual unit; the listing is for the complete box of four.

Q: What gap do these plugs come set to from the factory?
A: NGK specifies the gap for the R2556G-9 at 0.028" (0.7 mm). As with any racing plug, always confirm the correct gap for your specific engine combination with your tuner before installation, as racing applications may require gap adjustments.

Q: What torque should I use when installing these plugs?
A: NGK specifies 10.8–18 lb-ft for cast iron cylinder heads and 10.8–14.5 lb-ft for aluminum cylinder heads. Always use a calibrated torque wrench and apply anti-seize or follow your engine builder's recommendations regarding thread preparation.

Q: Why don't these plugs show up in a standard year/make/model fitment search?
A: The R2556G-9 is a racing-series plug without a standard OEM vehicle application listed in NGK's fitment database. Selection is based on matching the plug's specifications (heat range, thread dimensions, reach, electrode design) to your specific engine build. If you're unsure, contact our team or consult your engine builder — we're happy to assist.