The Spark Plug Story

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.

Hot Type B7HS
Has a larger surface exposed
to the combustion gasses.
Dissipates heat slowly.
Firing end heats up quickly

Cold Type B9HS
Has a smaller surface exposed
to the combustion gasses.
Dissipates heat quickly.
Firing end does not heat up quickly

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.

Examples of Spark Plugs

Please note the color of the insulator in the plug labled "correct".

Page 1 Exhaust Systems  
Page 2 Fine Tuning-Belts, Springs  
Page 3 Cylinder Kits  
Page 4 Variators  
Page 5 Final Drive  
Page 6 Carburators  
Page 7 Brakes  
Page 8 Tires  
Page 9 Front Suspension  
Page 10 Rear Suspension  
Page 11 Dual Head Light Mod  
Page 12 Corbin Seats  
Page 13 Rear Luggage  
Page 14 2008 Zuma Fix it Kit  
Page 15  
Page 16 Tech Tips
Page 17 Engine Work  


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