NGK Iridium IX Spark Plug - TR55IX
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The NGK TR55IX is an Iridium IX spark plug used in select automotive, marine, performance, and equipment applications where the engine manufacturer specifies the TR55IX / NGK 7164 plug profile. It is commonly used as an iridium upgrade from standard nickel TR-series plugs when the required reach, tapered seat, heat range, terminal style, and gap match the engine's factory specification.
This plug features NGK's fine-wire iridium center electrode design for strong ignitability, stable spark performance, and improved resistance to fouling in compatible engines.
Key Features
- Genuine NGK Iridium IX spark plug.
- NGK part number: TR55IX.
- NGK stock number: 7164.
- Iridium center electrode for stable spark and long service performance.
- Projected-tip design.
- Resistor-style spark plug.
- Solid terminal configuration.
- Thread diameter: 14 mm / M14 x 1.25.
- Thread reach: 17.5 mm listed / 18 mm class.
- Hex size: 5/8 in. / 16 mm.
- Seat style: tapered seat.
- Heat range: 5.
- Common preset gap reference: 0.059 in. / 1.5 mm.
- Used where the application chart calls for the TR55IX plug profile.
Application Compatibility
Common application context includes select engines that call for the NGK TR55IX / 7164 plug profile, including:
- Select General Motors LS-based V8 applications where specified
- Select 4.8L, 5.3L, 5.7L LS1/LS6, 6.0L, and 6.2L GM V8 applications where the plug chart calls for TR55IX
- Select Ford 4.6L and 5.4L V8 applications where specified
- Select EFI marine inboard and sterndrive engine applications where the engine manufacturer's plug chart confirms TR55IX
- Select performance, street, and marine applications using the correct TR-series tapered-seat plug geometry
Use this spark plug only where the manufacturer's spark plug chart specifically calls for TR55IX, 7164, or an approved equivalent.
Fitment Notice
Confirm fitment by exact year, make, model, engine, service manual, ignition system, and factory spark plug chart before ordering. Spark plugs with similar NGK part numbers can still differ in reach, gap, heat range, seat style, projected-tip design, terminal type, and electrode design. Installing the wrong plug can cause hard starting, misfire, poor idle, thread damage, overheating, piston contact, or ignition-system issues.
When This Part Needs Replacement
Replace spark plugs during scheduled tune-up service or whenever plugs are fouled, worn, fuel-soaked, oil-contaminated, cracked, corroded, damaged, or causing hard starting, rough idle, hesitation, misfire, reduced throttle response, or poor fuel economy. Marine engines, tow vehicles, and high-load applications should have spark plugs inspected regularly because ignition problems often show up first under acceleration or sustained load.
Installation Notes
Check the plug number and required gap against the engine's service chart before installation. The TR55IX uses a tapered seat, so it does not use a separate sealing washer. Install into clean, undamaged cylinder head threads and tighten to the engine manufacturer's torque specification.
Avoid adding anti-seize unless the engine or plug manufacturer specifically calls for it, as lubricant changes thread friction and can lead to over-tightening. If gap adjustment is required, adjust only the ground strap and avoid prying against the fine iridium center electrode.
Alternate/Superseded Part Numbers
- NGK TR55IX — spark plug part number
- NGK 7164 — NGK stock number
- TR55IX Iridium IX — product style reference
- TR5 — related NGK V-Power plug profile with a different electrode design and typical preset gap; verify before substitution
- TR55 — related NGK plug profile with different construction; verify by application chart before substitution
Parts Desk Insight
The TR55IX should not be selected only because an engine uses a GM LS, Ford V8, or marine V8 platform. The correct plug depends on the engine's required gap, ignition system, cylinder head thread style, heat range, and service chart. The wide 0.059 in. gap reference is common for TR55-style applications, but some engines require a narrower gap, especially after ignition updates, forced induction, or marine service changes.
Shipping: Ships same or next day for fast Canada wide shipping. ⚓
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 3–4 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
Returns & Satisfaction Guarantee
We stand firmly behind the quality of every product we sell. Your confidence matters to us — and we back it with a straightforward 30-Day Satisfaction Guarantee.
If you are not fully satisfied, you may request a return within 30 days of delivery. All returns must receive pre-approval prior to being sent back. Unauthorized returns will not be accepted.
To qualify for a return:
Item must be in new, unused condition
Product must be in its original packaging
All parts, components, hardware, manuals, and accessories must be included
Packaging must be undamaged and suitable for resale
Important:
Electronics are strictly inspected. No returns on open-box electronics. Exceptions may apply only with prior written approval. Any electronic unit that has been installed, powered, activated, or altered may not be eligible for return.
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