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This Moroso ignition wire sleeve uses a close-weave fiberglass sleeve with an outer layer of silicone and is designed to seal the wire completely. Rated to 650 degrees Fahrenheit, the sleeve comes on a 25-foot roll—you cut it to fit.

This MSD Pro-Heat Guard ignition wire sleeve is similar to Moroso’s, having a thick woven fiberglass core with a special silicone rubber coating. MSD claims the Pro-Heat Guard core can resist temperatures up to 1,000 degrees Fahrenheit. It is cut-to-fit as well.

Since most ignition wire sleeve is slip-fit and doesn’t fit tightly over the wire, manufacturers use a large diameter shrink sleeve material that fits over the boot and extends partially over the sleeve. That seals the actual wire sleeve to the boot. The shrink sleeve shown here is from Mallory.

Moroso makes these prenumbered ID shrink sleeves that will help you easily identify which wire feeds which cylinder. This can be extremely useful while performing engine maintenance.

To install the sleeves, one ignition wire boot must be removed; it doesn’t matter if it’s on the distributor cap end or the spark plug end. Measure the wire, then cut the sleeve approximately 1 to 1.5 inches shorter than the measured length. This will account for the plug boots. The sleeve material is easily cut to length with a pair of sharp scissors. Remember, it’s easier to cut a sleeve that's too long than trying to stretch a sleeve that’s too short.

Slide the sleeve over the ignition wire. It’s sort of like pushing a rope—sometimes it’s easier to massage the sleeve material over the wire so it doesn’t bunch up or kink. Be sure to add two sections of shrink tubing before you reinstall the boot (one for each end). If you decide to add the numbered ID shrink sleeve, now’s the time to do so. You’ll never get the shrink sleeve over a wire boot.

Slide one of the shrink sleeves over the boot and the sleeve. You can use a lighter to shrink the sleeve, but a heat gun is much better. An open flame can do the job too quickly and distort or burn the shrink sleeve. If any wrinkles are evident, simply apply more localized heat. Be forewarned: too much heat will distort the shrink sleeve. When it looks right, stop! This method applies to installing the numbered ID shrink sleeves.

This photos shows how a finished shrink sleeve should look. Follow the same procedure for the boot on the other end of the wire, then do the remaining ignition wires. It takes some time, but the end result is a set of wires that is protected against heat and voltage leaks—and wires that will pass the highest voltage possible to the spark plugs.

Here is what a finished number ID shrink sleeve looks like. Pretty slick, we think.

Even the world’s finest ignition wires have it tough. First, there are today’s high-power ignition boxes. As ignition power becomes stronger and spark plug gaps increase, the chances of crossfire and spark leakage increase. Then there is the ignition wire’s arch-nemesis: heat. If you’ve ever seen wire with cracked jackets or worse, melted on a header tube, you know what we’re talking about.

But you can protect your ignition wires from these forces of evil with a set of ignition wire sleeves. The sleeves are simply slip-on insulators that effectively protect your wires from high voltage and high heat. Typically, sleeves can add 8,000 volts of extra insulation and almost double that figure in crossfire prevention, plus excellent resistance to heat created by headers or exhaust manifolds.

There are a couple styles of ignition wire sleeves available. The more popular type uses a closely woven sleeve with a silicone outer jacket. The other has a loose-weave, breathable sleeve that won’t trap moisture between the wire and the sleeve. Both types of sleeves do a good job.

We’ll go over the process of installing sleeves over a set of wires, and how to seal them to both the spark plug boots and the distributor cap boots. Spark plug wire sleeves are inexpensive insurance against wire failure and are readily available at Summit Racing Equipment.

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Author: Wayne Scraba

Wayne Scraba is a diehard car guy and regular contributor to OnAllCylinders. He’s owned his own speed shop, built race cars, street rods, and custom motorcycles, and restored muscle cars. He’s authored five how-to books and written over 4,500 tech articles that have appeared in sixty different high performance automotive, motorcycle and aviation magazines worldwide.