As was previously stated, spark plugs are generally more important to spark quality than spark plug wires. Most spark plugs exhibit failure when exposed to a large load. Failure usually consists of either intermittent sparking or arc-over. Arc-over is when the spark occurs between the spark plug wire and the engine block, instead of at the plug tip. Arc over is exacerbated by the use of low-quality wires, or wires that have cuts in the insulation.As was previously stated, spark plugs are generally more important to spark quality than spark plug wires. Most spark plugs exhibit failure when exposed to a large load. Failure usually consists of either intermittent sparking or arc-over. Arc-over is when the spark occurs between the spark plug wire and the engine block, instead of at the plug tip. Arc over is exacerbated by the use of low-quality wires, or wires that have cuts in the insulation.

The load at which a spark plug fails is different for all spark plugs. With the EIS’s charging circuit, the more load you put on an engine, the more voltage will be applied to the plug. This is a beneficial situation: for a high compression engine, the voltage at the plug will be inherently higher (since there is more load). The detriment is that spark plugs and wires are only rated to a certain voltage (30-40,000 volts is typical), and can begin to “blow out” at around 40,000 volts. If that voltage is exceeded by a large amount for a long enough length of time, the spark plugs will either blow out, break down or arc to somewhere other than the electrode (often through the insulator directly to the engine block).

Your installation manual specifies the recommended gap for your engine application. This gap will be larger than a typical aircraft plug gap because of the higher energy output from the EIS. This is perfectly acceptable with our ignition charging method, since the high load of the cylinder pressure will allow the voltage to be quite high at the electrode; the gap will keep the plug from seeing an over-voltage situation.

The bottom line is this: the EIS system uses an inductive (long duration charge at battery voltage) charging method for the coils, which is completely different than the capacitive (short duration charge at higher-than-battery voltage) charging method used by other manufacturers. What may work well for these systems may not work well for ours. Our experience has drawn us to the following guidelines for spark plug application:

All aircraft spark plugs will work with the EIS. We have found that the REM37BY (or equivalent) plugs work the best because they are easier to gap to the range required and fit the broadest heat range recommended by the engine manufacturer. We strongly recommend that you verify the heat range for your engine and use the appropriate plug.

Automotive spark plugs vary widely in heat range applicability. The EIS system will work with properly adapted automotive spark plugs. You MUST verify that the automotive spark satisfies the heat range requirement of your engine. An improper plug heat range risks pre-detonation and severe damage to your engine. As a general rule, we do not recommend the use of automotive spark plugs in aircraft engines.

Return to List