HKS SUPER FIRE RACING MR45XLZ - 50003-MR45XLZ

The HKS Super Fire Racing MR45XLZ (part number 50003-MR45XLZ) is a premium iridium spark plug engineered for performance-oriented vehicles — including cars, trucks, and motorcycles — that demand more from their ignition system than a standard OEM plug can deliver. Designed as part of HKS's top-tier M-Series plug lineup, the MR45XLZ is built to satisfy the needs of enthusiasts and tuners who require reliable ignition performance under demanding conditions. Whether you're running a modified street car or pushing your engine harder on the track, these plugs are purpose-built for exactly that application.

Key Features & Benefits

• Iridium Core & Top Material: Both the core and top are constructed from iridium, a material known for its durability and ability to maintain a consistent spark over extended use — meaning less plug degradation and more predictable engine performance over time.
• M-Series Ultimate Plug Design: HKS developed the M-Series as their pinnacle spark plug line, specifically reinforcing ignitability, durability, and anti-insulation performance. For tuned engines that generate more cylinder pressure and heat, these qualities translate directly into more complete combustion and reduced risk of misfires.
• Reinforced Ignitability: Improved spark initiation means more consistent combustion events, which is especially important on modified or forced-induction engines where the air-fuel mixture is denser and harder to ignite reliably.
• Enhanced Durability: Iridium's hardness and high melting point help the electrode maintain its geometry longer than standard copper or platinum plugs, reducing the frequency of replacement intervals — a practical benefit for any serious build.
• Anti-Insulation Performance: The M-Series design addresses insulation resistance, helping to maintain a strong spark even under the heat and pressure cycles of a tuned or high-compression engine.
• M14x1.25 Thread Size: A widely used metric thread pitch found on a broad range of performance four-cylinder and six-cylinder engines, making these plugs applicable across many popular performance platforms.
• Broad Vehicle Compatibility: Rated for use in cars, trucks, and motorcycles, the MR45XLZ is a versatile plug that fits into the ignition systems of a wide range of performance-oriented applications.

Specifications

• Brand: HKS
• Part Number: 50003-MR45XLZ
• Series: Super Fire Racing M-Series
• Core Material: Iridium
• Top Material: Iridium
• Thread Size: M14x1.25
• Heat Range: 9
• Vehicle Service Type: Car, Truck, Motorcycle

Fitment

The HKS Super Fire Racing MR45XLZ uses an M14x1.25 thread size and a heat range of 9, which places it in the performance/cooler heat range category intended for modified or higher-output engines. It is listed as compatible with a broad range of cars, trucks, and motorcycles that use this thread specification. Because spark plug fitment is highly dependent on your specific engine's thread pitch, reach, and required heat range, we strongly recommend verifying compatibility with your engine before ordering. If you are unsure which heat range is correct for your current state of tune, please contact our team — selecting the wrong heat range can affect engine performance and longevity.

Note: This plug is part of a series that includes other heat ranges and thread configurations (such as MR40XLB, MR45HLZ, and others). Confirm the correct variant for your application.

What's in the Box

This listing covers the HKS Super Fire Racing MR45XLZ spark plugs (50003-MR45XLZ). Quantity per purchase — whether a single plug or a set — is confirmed at checkout. Multiple-plug set options (such as packs of 4 or 10) are consistent with how this part number is sold through various channels, so please confirm your desired quantity when ordering.

Why Buy from ThreePiece.us

• Free Shipping: Every order ships free — no minimum required, no hidden freight fees at checkout.
• Affirm Financing: Spread your purchase into manageable payments with Affirm financing, available at checkout. Great for stocking up on multiple plugs or ordering alongside other ignition components.
• Expert Fitment Help: Spark plug selection — especially for modified engines — can be nuanced. Our team is here to help you confirm the right heat range, thread size, and plug type for your specific build before you order.

Frequently Asked Questions

Q: What heat range is the HKS MR45XLZ?

A: The MR45XLZ is a Heat Range 9 plug. In HKS's numbering system, a higher heat range number indicates a cooler plug, which is generally suited for modified, turbocharged, or higher-output engines that generate more heat in the combustion chamber.

Q: What thread size does the MR45XLZ use?

A: The MR45XLZ uses an M14x1.25 thread size. Before purchasing, confirm that your engine's spark plug threads match this specification, as using an incorrect thread size can damage your cylinder head.

Q: Is this plug compatible with motorcycles as well as cars?

A: Yes — the HKS Super Fire Racing MR45XLZ is listed as compatible with cars, trucks, and motorcycles, provided the engine's thread specification (M14x1.25) and required heat range align with this plug.

Q: How many plugs will I receive per order?

A: Please confirm the quantity at checkout. This part number is available in various pack configurations. If you have questions about how many plugs you need for your specific engine, reach out to our team before placing your order.