Engine: Spark Plugs

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There are three main types of spark plugs: Copper, Iridium and Platinum.

Types

Copper Spark Plugs

Pro: Inexpensive ($1.50 ish), Very Good spark, good performance plug.
Con: Not very long lasting, you need to change them more often 15K miles or so.

Platinum Spark Plugs

Pro: Longevity - lasts longer than the coppers: 30 or 60K miles.
Con: Spark is not as good as Copper, costs more than copper.

Iridium Spark Plugs

Pro: Performance of copper longevity of Platinum.
Con: Typically the most expensive plug out of the three.

Characteristics

There are other characteristics of a spark plug that you need to consider as well.

Heat Range

The operating temperature of a spark plug is the actual physical temperature at the tip of the spark plug within the running engine. This is determined by a number of factors, but primarily the actual temperature within the combustion chamber. There is no direct relationship between the actual operating temperature of the spark plug and spark voltage. However, the level of torque currently being produced by the engine will strongly influence spark plug operating temperature because the maximum temperature and pressure occurs when the engine is operating near peak torque output (torque and RPM directly determine the power output). The temperature of the insulator responds to the thermal conditions it is exposed to in the combustion chamber but not vice versa. If the tip of the spark plug is too hot it can cause pre-ignition leading to detonation/knocking and damage may occur. If it is too cold, electrically conductive deposits may form on the insulator causing a loss of spark energy or the actual shorting-out of the spark current. Also The lower a heat range you use will help to lower combustion temps to a degree.

Choosing a Heat Range

There are many different theories as to how you should choose your heat range on for your 3S. The consesus is that you should go one heat range cooler for every 75 Hp above stock that you make. However, only you can determine what the proper heat range for your car will be. Most BPU cars will be fine with the stock heat range. However, when you start to make really big power / boost you need to start experimenting with colder heat ranges.

Gap

Spark plug gap is defined as the distance between the center electrode and the ground electrode

spkbb6.jpg

The effects of spark plug gap are as follows:

narrow-gap risk: spark might be too weak/small to ignite fuel;
narrow-gap benefit: plug always fires on each cycle;
wide-gap risk: plug might not fire, or miss at high speeds;
wide-gap benefit: spark is strong for a clean burn.

Generally, you want to use the widest gap possible that won't cause spark blowout.

Gapping Your Plugs

You should always check the gap before you install your plugs. However, be very careful when you gap your plugs! Certain plugs such as iridium plugs should not be gapped with a gap tool. Instead, most manufacturers suggest that you gently tap the ground electrode on a flat hard surface to decrease the gap. You should never stick any object in between the ground and center electrodes on an iridium plug!

Projected Tip

Cars running very high boost and / or nitrous should use a non-projected tip spark plug!

This article originated from a thread or post on 3000GT/Stealth International. (1947)