AEM 30-71XX Infinity Stand-Alone Programmable Engine Mangement System Full Manual - Manual (Page 279)

EFI Components 273
© 2014 AEM Performance Electronics
EFI Components
Spark Plugs
Spark plug selection affects engine performance. On forced induction engines, it is critical that
the proper heat range and gap is used. Heat range refers to the ability of the spark plug to
conduct heat away from the electrode to the engine. A plug that has high thermal conductivity
has a short insulator that comes in contact with a large portion of the metallic plug shell. This
large area allows the combustion heat to be carried through the plug shell to the cooling jacket of
the cylinder head. In the case of a hot plug, the insulator is recessed deeply into the plug shell
with minimal contact to the shell. The plug has low thermal conductivity due to the lack of contact
with the shell. The nose of the insulator should operate at between 400–850 degrees C.
Temperatures above 400 degrees C are desirable because at higher temperatures deposits
from carbon, lead or soot are burnt off. Temperatures of 850 degrees C and over should not be
exceeded because this is typically the point where detonation or auto ignition can occur. Lower
heat range plugs have a higher resistance to auto ignition while higher heat range plugs have
less tendency to foul.