AEM 30-71XX Infinity Stand-Alone Programmable Engine Mangement System Full Manual User Manual

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Infinity User Manual

The spark plug gap on forced induction engines should be reduced REGARDLESS of the type
of ignition system. We have read many instruction manuals for aftermarket ignition systems that
recommend that the plug gap be opened up for better flame propagation. Although this
recommendation may have had some merit when vehicles had carburetors, it does not apply to
modern engines with electronic engine management systems. The smaller gap on forced-
induction engines requires less spark energy to arc across the ground and the electrode and has
a lesser tendency to misfire under the extreme pressures of a racing engine combustion
chamber. Also there are spark plugs made with exotic fine wire highly conductive center
electrodes that require less energy to fire such as the Denso Iridium that are well suited to racing
conditions. The following is a chart of gap sizes for various engines on gasoline:

Naturally Aspirated up to 11.0:1 CR:

1.1mm (.044”)

Naturally Aspirated 11.0:1 to 14.0:

0.8mm (.032”)

Forced Induction to 20-PSI:

0.7mm (.028”)

Forced Induction to 40-PSI:

0.6mm (.022”)