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The spark plug in your Zuma has
two primary functions: 1. To ignite the air/fuel mixture 2. To remove heat out of 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. Additionally, 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 selelcted. A spark plug cannont create heat! It can only remove heat. The spark plug works as a heat-exchanger by pulling unwanted thermal energy away from the combustion chanber 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: 1. The insulator nose length 2. Gas volume around the insulator nose 3. Materials/construction of center electrode and porcelain insulator The Gap of the spark plug is extemely important.Always check the gap on every plug before installation;plugs are not always pre-gapped at the factory. The correct gap for the Zuma is: 0.020~0.030"(0.6~0.7mm). Spark Plug Torque is often overlooked. It is most critical as it directly influences spark plug temperatures. A spark plug can only transfer heat effectively when it is fully seated on the cylinder head. The correct torque for the Zuma is 14.0lb-ft (2.0kg-m) The recommended factory plug for a bone stock Zuma, (not modified) is an NGK BPR7HS. For a modified Zuma a BPR8HS, and for a fully modified racing Zuma BPR8HIX. |
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The insulator nose length is
the distance from the firing tip of the insulator to the point
where insulator meets the metal shell. Since the insulator tip
is the hottest part of the spark plug, the tip temperature is
a primary factor in pre-ignition and/or fouling. The tip temperature
must remain between 450C~850C. If lower the insulator area surrounding
the center electrode will not be hot enough to burn off carbon
and combustion chamber deposits. This can lead to misfire and
fouling. If the tip temperature is higher than 850C the plug
will overheat which can lead to pre-ignition detonation and big
time engine damage.  |
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