Excerpt from the NGK site.
SPARK PLUG BASICS:
The spark plug has two primary functions:
- To ignite the air/fuel mixture
- To remove heat from the combustion chamber
Spark plugs transmit electrical energy that turns fuel into working energy. A sufficient amount of voltage must be supplied by the ignition system to cause it to spark across the spark plug's gap. This is called "Electrical Performance."
The temperature of the spark plug's firing end must be kept low enough to prevent pre-ignition, but high enough to prevent fouling. This is called "Thermal Performance", and is determined by the heat range selected.
It is important to remember that spark plugs
do not create heat, they can only
remove heat. The spark plug works as a
heat exchanger by pulling unwanted thermal energy away from the combustion chamber, and transferring the heat to the engine's cooling system. The heat range is defined as a plug's ability to dissipate heat.
The rate of heat transfer is determined by:
- The insulator nose length
- Gas volume around the insulator nose
- The materials/construction of the center electrode and porcelain insulator
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Summary:
Since the EKs are longer than the E's, approx. 2mm longer. It has better heat exchange characteristic. The gas volume also will change since the E is shorter. The EK's also have double electrodes for better spark spread.
I'd say change it back to the specified CR9EK plug. You might regain about a horse or 2 that you lost changing it to the E.
