By: Brian Lin

For an engine to operate, a good supply of air laden with oxgen, fuel and good spark plugs are needed to ignite the mixture. The two main components of a plug are the ceramic casing which is a good insulator and the electrodes from the central tip and the negative pick up contact which is connected to the engine block.
A spark plug with good ceramic casing allows it to spark at the tip rather than it shorting out inside the plug core. When replacing the sparks by yourself, be very careful working on any part of a car's high tension circuit and never work on it with the engine running. Many cold start faults are caused by faulty plugs or HT leads.

Spark plug construction
A spark plug is composed of a shell, insulator and the conductor. It pierces the wall of the combustion chamber and therefore must also seal the combustion chamber against high pressures and temperatures, without deteriorating over long periods of time and extended use.

High Performance HT (high tension) Leads
Faulty high tension leads - (HT leads) will not cause a weaker spark but will just prevent the spark from happening so if you are having a misfire or uneven idle make sure the HT leads are in good order - flexing and bending them is often enough to damage them so make sure that they are handled carefully. A set of good quality HT leads will minimize electrical faults especially in extreme temperatures but will not in themselves increase performance.

The HT leads should have the lowest internal resistance and also provide electromagnetic shielding to prevent electrical interference with other car components such as the main engine control unit (including the radio). The lead should be matched to the voltage as the wrong size core can lead to heat problems and resistance issues. A sports core size will be as large as 8.5 mm whereas a street tuned car will probably get away with 7 or 8 mm core sizes. Most HT lead suppliers can assist you in choosing the right length and core size for your cars application.

Performance ignition coils and coil packs.
Just as a power transformer converts mains 240 volts into a usable 9 volts for your charger or appliance a coil will increase the voltage in some installations up to 40,000 Volts) allowing the creation of a spark which can jump the gap between the plugs. In some modern engines there is a separate coil pack with a separate coil or each spark plug's faulty coil can also reduce the spark voltage to the point that no spark happens and you end up with a misfire.

Sports coils increase the power to the plug and allow a larger spark so match a sports coil with a larger plug gap. Timing the spark is critical too early (premature ignition) and the engine could be damaged and too late and the compression will be lower as the exhaust port opens potentially causing damage to the cat & exhaust as combustion move down along the exhaust.

Ideally you want to create a spark inside the cylinder of the engine and expose as much of the spark as possible to the compressed air and fuel mixture. Ideally the electrodes should be as thin as possible and be good conductors of electricity and the voltage should be as high as possible. Spark plug technology has really moved on in recent years and iridium-equipped plugs allow an ultra fine electrode, last for up to 40,000 miles and are superb conductors of electricity.

Ignition system maintenance
A good steady power supply is vital for a good strong spark, common problems in an old engine are actually caused by a bad earth connection (actually just the connection to the - or + battery terminal). Power regulators are available which ensure that a constant voltage is always available. If you have a large ICE install and lots of other power draining accessories you may find that on a cold day when a battery typically struggles it will fail so ensure you have a battery with a large cranking power which although only gives 12V, it will do so in a much more steady manner and be more resilient to adverse conditions.

Ensure that the spark plugs are clean and in good condition as the terminals may well glaze and lose their conductivity to a small degree over time (expensive plugs are typically more resistant to glazing and can be left for longer periods of time). So every six months or so it can be beneficial on normal plugs (we are not here referring to iridium or performance/long life spark plugs) to deglaze them by rubbing them over with a wire brush and fine grade of sandpaper. This keeps the conductivity of the contact points and ensures a strong spark thereby maintaining both performance and economy.