Insulated Plug Wire Sleeve - Ultra 40 Black

The MOROSO Insulated Plug Wire Sleeve – Ultra 40 Black is a fiberglass and silicone composite heat shield designed to protect spark plug wires from extreme engine temperatures and electrical interference. This 25-foot sleeve accommodates 8.65mm wires and delivers the thermal management and signal integrity that performance engines demand, whether on the track, in the shop, or under the hood of a heavily modified vehicle.

The Ultra 40 construction combines high-temperature fiberglass with silicone elastomer to withstand sustained heat exposure while preventing capacitive coupling that degrades ignition timing. The black finish blends into engine compartments while the material's flexibility allows for easy routing around tight spaces and tight bends without cracking or peeling. At 25 feet of continuous coverage, this sleeve provides enough length to protect multiple cylinders or to route a single wire across the full engine width with room for custom configurations.

This wire sleeve is essential for builders upgrading ignition systems on street rods, drag cars, marine engines, and carbureted or fuel-injected platforms where proximity to exhaust manifolds or turbo housings creates thermal stress. It's equally valuable in vintage restorations where factory wiring lacks adequate shielding. The 8.65mm inner diameter matches standard high-performance spark plug wire sizes, ensuring a snug fit that minimizes movement and vibration-induced wear.

Wire sleeves of this type are standard in racing and engine building circles—they're not optional upgrades but engineering necessities when spark plug wires are routed near heat sources. MOROSO's Ultra 40 formula is recognized for maintaining flexibility at elevated temperatures, a critical trait since brittle sleeves can split under thermal cycling and leave wires exposed to both heat damage and EMI contamination.