NGK 91874 Laser Iridium Spark Plug BMW 550i 650i 750i 760Li X5M X6M Rolls-Royce Ghost

The NGK 91874 (SIZKBR8B8HG) is an NGK Laser Iridium High Ignitability Spark Plug engineered as a factory-spec replacement for BMW N63B44 V8 and N74B66 V12 engines, plus the Rolls-Royce Ghost 6.6L V12. These are direct OEM-grade plugs manufactured in Japan to BMW's tight tolerances, offering 100,000-mile service life with a laser-welded iridium center electrode and platinum ground electrode. Sold individually. NGK 91874 is the correct plug for BMW 550i, 650i, 750i, 750Li, 760Li, X5 M, X6 M, M5, M6, and Rolls-Royce Ghost applications listed below.

NGK Laser Iridium: OEM-Grade Performance, 100,000-Mile Life

NGK's Laser Iridium series is not a performance upgrade; it is a premium OEM-replacement plug that matches or exceeds factory specifications. The iridium center electrode is laser-welded to a 0.6mm fine-wire tip, reducing the voltage required to fire the plug and producing a more consistent, complete combustion event on every stroke. The platinum ground electrode resists erosion across the full service interval.

BMW specifies Laser Iridium plugs for the twin-turbocharged N63B44 and N74B66 engines for a reason: these high-output, direct-injected V8 and V12 applications demand a plug that fires reliably under boost, resists fouling during the N63's warm-up enrichment cycle, and lasts through extended service intervals. SIZKBR8B8HG delivers exactly that.

• Laser-welded 0.6mm iridium center electrode for consistent, high-energy spark
• Platinum ground electrode for extended service life
• Extended (projected) tip design improves ignitability and self-cleaning
• 5k Ohm resistor suppresses EMI interference with BMW electronics
• Preset 0.8mm (0.031 in.) gap, factory-calibrated; do not adjust
• 100,000-mile OEM-grade service life
• Manufactured in Japan

Laser Iridium vs. Iridium IX: Know the Difference

NGK produces two iridium spark plug lines, and they are not interchangeable for this application. The Laser Iridium series (SIZKBR8B8HG) is the OEM-spec plug designed for BMW and Rolls-Royce factory service. It uses a laser-welded iridium center electrode with a platinum-tipped ground electrode, is preset at the factory gap, and is not to be adjusted. The Iridium IX is an aftermarket performance plug with a different electrode geometry and gap spec; it is not BMW-specified for the N63B44 or N74B66 engines. For correct OEM replacement, use Laser Iridium.

How Many Plugs Do You Need?

This listing is for one (1) spark plug. The number of plugs per vehicle depends on engine configuration:

• BMW N63B44 V8 (550i, 650i, 750i, 750Li, X5, X6, M5, M6): 8 plugs per complete set
• BMW S63B44 V8 (X5 M, X6 M, M5, M6): 8 plugs per complete set
• BMW N74B66 V12 (760Li): 12 plugs per complete set
• Rolls-Royce Ghost 6.6L V12: 12 plugs per complete set

Adjust quantity at checkout. BMW N63 owners: replace all 8 plugs as a set at the same service interval to maintain even ignition timing across all cylinders.

Fitment BMW N63B44 / N74B66 and Rolls-Royce Ghost

SIZKBR8B8HG fits BMW 5 Series, 6 Series, 7 Series, X5, X6, M5, and M6 models equipped with the N63B44 4.4L Twin-Turbo V8 or S63B44 4.4L Twin-Turbo V8, plus the BMW 760Li with N74B66 6.0L V12 and the Rolls-Royce Ghost with N74B66 6.6L V12. Verify your engine code on the underhood sticker or via VIN decoder before ordering. The N63B44A (early build) variant may use sibling part SIZKBR8A8HS -- see FAQ below.

Full Specifications NGK 91874 SIZKBR8B8HG

What's Included

• 1x NGK Laser Iridium Spark Plug SIZKBR8B8HG (91874)

One plug per order. Order 8 for a complete set on all N63B44 or S63B44 V8 applications. Order 12 for a complete set on all N74B66 V12 applications (BMW 760Li, Rolls-Royce Ghost).

SIZKBR8B8HG vs. SIZKBR8A8HS (NGK 1555): Which One Do You Need?

NGK produces two closely related Laser Iridium plugs for the N63 engine family. The SIZKBR8B8HG (91874) is the current production plug for the N63B44 engine in its updated form, covering 2009-2015 applications as listed in the fitment table above. The SIZKBR8A8HS (NGK 1555) is the predecessor plug designed for early N63B44A applications. The two plugs share the same heat range, thread size, and reach, but differ in electrode design and are not interchangeable. Always verify your engine build date and engine code variant before ordering. If your BMW dealer or independent BMW specialist has previously used SIZKBR8A8HS, check your engine code variant to confirm the correct current-spec plug before switching.

Installation Overview BMW N63 and N74 Spark Plug Replacement

Replacing spark plugs on the BMW N63B44 is more involved than a typical plug swap. The N63 is a "hot vee" twin-turbo V8, meaning the turbos sit in the valley between the cylinder banks and the intake manifold must be partially or fully removed to access the rear bank plugs. Allow 3-5 hours for a complete set replacement if you have BMW-specific experience. The N74B66 V12 in the 760Li and Ghost is a similarly complex procedure and is typically best left to a BMW or Rolls-Royce specialist.

• Torque spec: 25 Nm (18 lb-ft) do not overtighten the 12mm thread
• Gap is preset at 0.8mm from the factory -- do not attempt to adjust
• Use a small amount of anti-seize on threads only if your torque wrench cannot confirm a dry torque spec; NGK generally recommends dry installation per spec
• N63 rear bank requires intake manifold removal for full plug access on most build dates
• Replace all plugs in the bank or full set at the same service interval
• Recommended service interval: BMW specifies 60,000 miles for the N63 engine; many enthusiasts replace at 30,000-45,000 miles given the N63's thermal demands

Warranty and Regulatory Information

This plug carries a 60-day limited warranty against manufacturing defects. As an OEM-grade plug with a 100,000-mile rated service life, premature failure under normal operating conditions within that interval is covered. Retain your purchase receipt.

California residents: This product contains chemicals known to the State of California to cause cancer and reproductive harm. See www.p65warnings.ca.gov.

About NGK Spark Plugs

NGK is the world's largest manufacturer of spark plugs and is the OEM supplier to BMW, Toyota, Honda, Nissan, and dozens of other manufacturers. The Laser Iridium series represents NGK's highest-grade replacement plug line, built to exacting tolerances using materials and processes developed for factory fitment. Every SIZKBR8B8HG plug is manufactured in Japan and meets or exceeds the original factory specification for N63B44 and N74B66 applications.

Frequently Asked Questions

What spark plug gap does NGK 91874 come set to, and can I adjust it?
The gap for SIZKBR8B8HG is 0.8mm (0.031 in.), set at the factory during manufacturing. Do not attempt to adjust the gap on any NGK Laser Iridium plug. The laser-welded iridium electrode is extremely fragile and will be damaged by any gap tool contact. Install the plug at the factory-set gap exactly as received.

How often should I replace spark plugs on a BMW 550i, 750i, or X5 with the N63B44 engine?
BMW's official service interval for the N63B44 is 60,000 miles. Many experienced N63 owners and independent BMW specialists recommend shortening this to 30,000-45,000 miles given the N63's elevated operating temperatures, oil consumption characteristics, and the labor cost of a late replacement. Plugs left in too long on turbocharged direct-injection engines can seize in the head and cause significant damage on removal.

How many spark plugs do I need for my BMW N63B44 V8?
The N63B44 is an 8-cylinder engine and requires 8 spark plugs for a full set. This listing sells one plug at a time. Set your quantity to 8 at checkout for a complete engine service. The BMW 760Li and Rolls-Royce Ghost V12 require 12 plugs per full set.

What is the difference between the N63B44 and S63B44 engines? Do they use the same plug? 
The 91874 is the standard twin-turbo 4.4L V8 found in the 550i, 650i, 750i, 750Li, X5 xDrive50i, and X6 xDrive50i. The S63B44 is the high-output M-tuned version of the same architecture used in the X5 M, X6 M, M5, and M6. Both engines are listed in the fitment table above and use SIZKBR8B8HG (91874). Confirm fitment by engine code before ordering.

What is the difference between NGK Laser Iridium and NGK Iridium IX?
Laser Iridium plugs are OEM-spec replacement plugs with a laser-welded fine-wire iridium center electrode and a factory-preset gap. Iridium IX is a separate NGK aftermarket performance line with a different electrode geometry and a gap spec intended for adjustment. BMW specifies Laser Iridium for the N63B44 and N74B66 engines. Using Iridium IX in place of Laser Iridium is not a BMW-approved substitution and may affect ignition timing, emissions, and long-term reliability on these engines.

Will aftermarket spark plugs void my BMW warranty?
Under the federal Magnuson-Moss Warranty Act, an aftermarket part cannot void your factory warranty unless the manufacturer can demonstrate that the specific aftermarket part caused the specific failure being claimed. Replacing worn plugs with OEM-equivalent NGK Laser Iridium plugs at the correct service interval is unlikely to affect any BMW warranty claim. For vehicles still under factory warranty, consult your dealer if you have concerns about documentation.

Do I need to replace spark plugs on both banks at the same time on the N63?
Yes. On any multi-cylinder engine, replacing plugs as a complete set ensures consistent ignition timing across all cylinders. On the N63B44 in particular, where rear-bank access requires intake manifold removal, replacing all 8 plugs in one service saves significant labor cost compared to returning to finish the other bank later.

What is the SIZKBR8A8HS, and is it the same as SIZKBR8B8HG?
SIZKBR8A8HS (NGK stock number 1555) is the predecessor Laser Iridium plug for early N63B44A engine variants. While both plugs share the same heat range, thread dimensions, and reach, they are distinct part numbers with different electrode specifications and are not interchangeable. Check your engine's build date and exact N63 variant designation before choosing between the two. When in doubt, consult an independent BMW specialist or the NGK application guide using your VIN.

Is this plug compatible with the Rolls-Royce Ghost?
Yes. The 2011-2013 Rolls-Royce Ghost uses a BMW-derived N74B66 6.6L twin-turbo V12 engine. SIZKBR8B8HG is the correct Laser Iridium replacement plug for this application. A complete set requires 12 plugs. Rolls-Royce specialist service is recommended for plug replacement on the Ghost given engine access complexity.

What is the thread size and reach for NGK91874?
SIZKBR8B8HG uses a 12mm x 1.25mm thread pitch with a 25.2mm reach. These dimensions match the N63B44 and N74B66 cylinder head specifications exactly. Do not substitute a plug with a different reach -- an incorrect reach can cause the electrode to protrude into the combustion chamber or sit recessed, both of which damage the engine.