Moroso 28330 Ultra 40 Spark Plug Wire Set for Harley-Davidson XL Sportster

The Moroso 28330 Ultra 40 is a high-performance motorcycle ignition wire set engineered for Harley-Davidson XL Sportster applications. Trusted at the highest levels of motorsport — from dual-mag Top Fuel dragsters to NASCAR Cup Series competitors — the Ultra 40 sets the benchmark for performance spark plug wires.

At the heart of the Ultra 40 design is an 8.65mm diameter, spiral-wound nickel/copper alloy conductor wrapped at the optimum ratio to deliver the highest possible spark energy while keeping electromagnetic (EMI) and radio frequency (RFI) interference to an absolute minimum. With 40 ohms of resistance per foot, these wires strike the ideal balance between energy transfer and noise suppression.

Key Features:

• 8.65mm diameter spiral-wound nickel/copper alloy conductor for maximum energy transfer
• 40 ohms resistance per foot — optimized for both performance and EMI/RFI suppression
• Kevlar core rated four times stronger than standard aramid fiber cores for exceptional dielectric strength
• Extra-thick EPDM insulation layer for superior dielectric strength and UV resistance
• Closely woven fiberglass, silicone-impregnated outer jacket adds up to 8,000 volts of additional insulation protection
• High-temperature silicone boots rated to withstand extreme heat
• Extra-thick construction guards against exhaust header heat, chafing, and contaminants
• Replaces OEM H-D part number 31958-04
• Made in the USA

The Moroso Ultra 40 motorcycle ignition wire set is a direct-fit, race-proven upgrade that delivers reliable spark energy and long service life — whether on the street or the strip.