Autolite Ground Electrode Designs

Ground electrodes come in a variety of shapes and sizes.

Standard spark plugs typically feature a traditional ground electrode. Ground electrode variations include cut back, shield strap, surface discharge, and taper cut.

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A cut back ground electrode serves a similar function to a taper cut ground, fine wire ground and angled ground electrode. All trimmed designs have the same purpose: to reduce quenching and shadowing by reducing the surface area between the electrodes which could hinder the growth of the flame nucleus.

Autolite uses a one-piece ground shield strap design on their HT (High-Thread) plug for improved heat transfer.

True surface discharge or surface gap spark plugs have no side electrode, instead utilizing the entire face of the plug shell as a ground to ignite. Thus the gap remains constant through the plugs entire life. They have no given heat range as the electrode design prevents the firing tip from overheating, and the insulator is flush with the metal shell to dissipate heat quickly. Therefore, these plugs are susceptible to fouling in cold applications.

Surface discharge plugs may be required in high compression applications or with high energy ignition systems. They are also used in rotary engines as they present a flush face to the combustion chamber, eliminating interference with an electrode tip and exposing the spark to the entire air/fuel mixture for improved combustion.

Many variations of the surface discharge plug exist, including the semi-surface discharge, intermittent gap, supplementary gap, and surface air gap plug. All designs create a spark along the insulator nose to remove carbon build-up.

A taper cut ground electrode serves a similar function to a cut back ground, fine wire ground and angled ground electrode. Also known as an inverted v-tip, tapered v-profile, trimmed side, v-trimmed or wedge shaped ground electrode, all trimmed designs have the same purpose: to reduce quenching and shadowing by reducing the surface area between the electrodes which could hinder the growth of the flame nucleus.