NGK V-Power Spark Plugs TR55 3951

The **NGK V-Power Spark Plugs TR55** (part number 3951) are high-quality, nickel-tipped spark plugs designed for reliable performance, improved ignitability, and cost-effective replacement in a wide range of gasoline engines. They are a popular upgrade or OE-style option for many vehicles, including classic Mustangs, GM LS-series applications, marine engines like Indmar 8.1L Vortec, and various other cars and trucks.

### Key Features:
– **Patented V-Power (V-Groove) Design**: Features a unique V-cut in the center electrode that directs the spark to the edge, allowing the flame kernel to develop more rapidly for better ignition efficiency and reduced misfires.
– **Enhanced Ignitability & Performance**: Provides superior spark focus compared to standard plugs, lowering ignition system voltage requirements while delivering smoother operation, especially under load.
– **Trivalent Metal Plating**: Offers excellent anti-corrosion and anti-seizing properties, making installation and removal easier while protecting against rust and damage.
– **Projected Tip & Copper Core**: The center electrode uses a copper core for excellent heat dissipation, combined with a projected tip for strong anti-fouling characteristics and improved combustion.
– **Resistor Type**: Built-in 5k Ohm resistor to suppress electromagnetic interference and protect sensitive electronics.

### Specifications:
– Thread Size: 14mm
– Thread Pitch: 1.25mm
– Reach: ~17.5–18mm (0.689–0.709 in.)
– Seat Type: Tapered
– Hex Size: 5/8 in. (16mm)
– Heat Range: 5 (NGK scale – mid-range, suitable for many naturally aspirated and mildly modified engines)
– Terminal Type: Solid (removable nut on some variants)
– Electrode Material: Nickel with V-cut center electrode

These plugs strike an excellent balance between everyday drivability, fuel efficiency gains, and durability—making them a trusted choice for both stock replacements and performance-oriented builds. Always verify fitment for your specific vehicle using NGK’s application guide or your vehicle’s requirements.

If you’re installing them, NGK recommends torquing to 10.8–18 lb-ft in cast iron heads or 7.2–14.5 lb-ft in aluminum heads (use anti-seize as needed).