Description

Genuine NGK LMAR8BI-9 (91909) Laser Iridium Spark Plug — Specifications, Features & Applications

The NGK LMAR8BI-9, carried under stock number 91909, is part of NGK’s Laser Iridium range — the brand’s OE-grade line built for sport bikes and performance motorcycles rather than everyday economy applications. Its laser-welded fine-wire iridium tip fires with far less voltage than a conventional plug, delivering a stronger, more complete spark that translates into crisper throttle response, cleaner idle, and more consistent combustion at the higher RPMs these engines are built to run.

This plug is a common OE-spec fitment for 10 mm thread engines with a heat range 8 rating, and it’s frequently specified for the Suzuki Hayabusa (GSX1300R), the current-generation Suzuki GSX-8S and GSX-8R, Suzuki V-Strom models, and a range of other Suzuki and Yamaha motorcycles that call for this exact plug.

Technical Specifications

Attribute	Detail
Brand	NGK
Part Number	LMAR8BI-9
Stock Number	91909
Series	Laser Iridium
Center Electrode	Iridium, fine wire, laser-welded
Ground Electrode	Platinum-tipped, single
Gap	0.9 mm (0.035″), factory pre-set
Thread Diameter	10 mm (M10)
Thread Pitch	1.0 mm
Reach	26.5 mm (1.04″)
Hex Size	14 mm (9/16″)
Heat Range	8
Seat Type	Gasket seat
Terminal	Threaded stud
Resistor	Yes
Insulator	Pure alumina silicate ceramic

Key Features

A laser-welded fine-wire tip built for high RPM. The iridium center electrode is precision laser-welded rather than crimped, holding its shape and gap far more reliably at the sustained high engine speeds sport bikes are designed for. This lowers the voltage needed to fire the plug and keeps ignition consistent even when the engine is being pushed hard.

Platinum-backed ground electrode for even wear. Unlike plugs that rely on a plain nickel ground strap, the LMAR8BI-9 carries a platinum disc welded to the ground electrode, which resists erosion far longer and keeps the gap accurate over extended high-performance use.

Durability well beyond standard plugs. Iridium’s hardness and resistance to electrical erosion mean this plug is built to go the distance — NGK positions the Laser Iridium line for lifespans in the 80,000–100,000 mile range on applications where it’s OE-fitted, translating on a bike to significantly longer service intervals than a nickel plug.

Stronger, more complete combustion. The fine-wire tip concentrates spark energy more efficiently, improving ignitability and giving a noticeable bump in acceleration and throttle crispness compared to a standard plug — a difference riders typically notice immediately after swapping in.

A mid-range heat range for real-world riding. Heat range 8 sits in the range Suzuki and Yamaha spec for these engines, balancing enough heat dissipation for spirited, high-RPM riding against enough warmth to resist fouling during stop-and-go city use.

Reinforced insulator, less risk of misfire. The high-grade alumina silicate ceramic insulator is built to resist dielectric punch-through — where a spark exits through the side of the plug instead of the tip — which keeps performance consistent as mileage builds up.

Corrosion-resistant shell. Trivalent plating on the plug body protects against rust and seizing, so the plug comes out cleanly at your next valve service instead of fighting you in the head.

Motorcycles using NGK LMAR8BI-9

The following motorcycles are known to use the LMAR8BI-9 as OEM or a direct replacement:

 

If your bike isn’t listed above but calls for a 10 mm (M10) thread, 26.5 mm reach, and heat range 8 plug, the LMAR8BI-9 will very likely be a correct match — though as with any plug swap, it’s worth cross-checking against your bike’s spec sheet or the plug currently fitted, since Suzuki and Yamaha don’t always share identical specs even across similarly sized engines.