Choosing Performance Spark Plugs

A range of high performance spark plugs exist on the market. Some claiming the highest temp, some hot and cold, with different electrode materials, design, and different spark gaps.

Deciding what is best may be an uphill struggle, as manufacturers recommend certain types, however when looking for performance, spark plugs are an important part of the 4 cycles of engine operation.

Contents

  • Overview of Spark Plugs
    • Plug Types & Materials
    • Electrode Design
  • What is a cool/hot spark plug and why would you choose one over the other?
  • What types of spark plug enhance performance?
  • How does the spark plug affect the flame front/combustion profile?
  • Resistive plugs & Plugs that boost sparks. Any good for performance gains, or just a gimmick?
  • Care for spark plugs, gapping, and cleaning - is it still required?

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Plug types

Copper

With a copper core and a nickel alloy tip for the electrode, these have a lower maximum temperature at around 1083°C for Nickel and 1450°C for Copper.

As a result, electrode tips break down quicker and after 10,000 you could see a bigger electrode gap emerging. Gaps can cause misfires in your cylinders and damage to wiring and ignition coils.

Platinum

For a very high melting point (around 1770°C), platinum is used for the very tip of the electrode, usually in the form of a disc.

It is ideal for long use cases and does not see any wear for 30-40,000 miles. Hotter temperature resistance means platinum spark plugs are cleaner, as less carbon build up occurs.

Iridium

Its properties are harder with Iridium over Platinum, with an exceptional melting point of around 2,450°C too.

Lasting even longer than platinum plugs, with a highly efficient electrode tip setup of smaller diameter over Platinum plugs. This also makes fuel burn quicker and is great for performance applications.

Electrode Design

For grounding, the electrode is available in a number of designs depending on your needs.

Center Electrode

With a traditional center electrode being the most common, it is a ‘J’ design coming from the side of the plug and looping over the center of the tip of the plug for optimum spark.

Double Fine Wire (DFE)

Adding a thin wire to both the pin on the electrode tip and in the center of the electrode results in less voltage needed to jump the air gap for a spark. Good for fuel economy and power.

This design on a nickel plug does not have a long life though. It is often paired with platinum or iridium electrode tips and can outlast a traditional plug.

Flat

Which is smaller and does not extend out the end of the plug, it is close to the center electrode and a smaller journey for the spark to jump and dissipate heat away from the electrode.

Excellent in harsh environments that undergo a lot of vibration.

Hybrid

Engines that are prone to higher carbon deposits use Hybrid electrode designs.

With two additional grounding electrodes that are used as a backup once carbon deposit is too much on the original electrode.

It can even switch back to its original electrode once the carbon build up is gone, ideal for harsh environments.

Low Angled

A lower profile than a standard ground electrode, this angled version is the solution for a quicker path and dissipates heat better, with more vibration resistance too. It needs a lower voltage for sparking and can improve power and fuel economy for an engine.

Multi-Ground

With two main ground electrodes, these are used in rotary engines or in applications with a lean air-fuel ratio (such as industry applications).

These are prone to misfiring due to erosion of the electrodes which causes larger spacing between them, becoming more difficult to jump the gap.

Multi Ground Electrode spark plugs can have 2, 3 or 4 prong designs. However, all these designs will only produce a single spark.

Projected Square Platinum

Otherwise known as ‘PSPE’, a platinum square is designed into the tip of these for better focus of the spark.

Occurring between the center electrode, where a fine wire is placed at the platinum ground electrode.

Semi-Surface Discharge

Voltage path in this design just touches the insulating area.

During discharge, excess carbon is burned off. It has a wider gap, but this is better for ignition and not as prone to creating wider gaps.

Slant

A lower profile design coming from the edge of the spark plug shell, that is close to the center electrode. Ideal for heat dissipation and good for vibration.

Square Precious Metal

An entire piece of platinum is welded to the edge of the ground electrode for a long lasting solution.

Surface Discharge

Without a side electrode, these versions rely on the face of the plug being the grounding point.

With a consistent gap during its lifetime, these are unique as they are without a rated temperature, and not suitable in cold applications due to being prone to carbon build up.

Used primarily in rotary and high energy engines due to their flat face designs.

Taper Cut

Can be called inverted v-tip, tapered v-profile, trimmed side v-trimmed or wedge designs, these are known for the same characteristics as a cut background or fine wire ground electrode design.

Trapezoid Cut

Similar to tapered cut, as highlighted above. A cut off design reduces flame concentration as the surface area between electrodes is reduced here.

U-groove

Only part of Denso plugs with a patented design, these offer ignition improvement and less quenching. Allowing flame propagation and a better combustion cycle.

Cool vs Hot Plugs

Cool spark plugs dissipate heat away from the plug tips, reducing its overall temperature. Whereas hot spark plugs keeps heat at the tip of the electrode.

The heat range of a plug is indicated by a number.

Choosing a spark plug is getting the balance for idling conditions and hot enough that does not produce ‘fouling’ (deposit build up) and cool enough for reducing possible engine knocking for peak power.

It is important in race applications, deciding that a cooler plug is preferable as it might make the difference in lap times.

What types of spark plug enhance performance?

Iridium offers the slight improvement in horsepower and performance of a race engine; this is due to its highly efficient electrode producing a ‘cleaner’ spark with its high operating temperature in the cylinder block.

Frequently asked questions about spark plugs

Spark plug internal

How does the spark plug affect the flame front/combustion profile?

The smaller the gap, the better combustion (for high injection pressured engines). This can result in self-ignition though, which damages the engine.

In contrast, the larger the gap, the more prone to misfiring. It will also not be as efficient to ignite fuel in low pressure injection engines either.

High pressure injection systems will give a smoother flame front, which means a combination of spark and the injection pressure are important factors to consider.

Resistive plugs & Plugs that boost sparks - Good for performance gains, or just a gimmick?

With a lot of marketing and promises from spark plug manufacturers, ultimately the performance spark plugs do not increase performance of an engine.

Noble plugs (from material that does not corrode) are premium, expensive options that can be considered.

Materials such as platinum, do offer slight advantages over standard plugs, but only in high performance race applications. This is where you will see the small advantage in power, but this will be negligible.

Care for spark plugs, gapping, and cleaning - is it still required?

Modern ‘off the shelf’ spark plugs for your engine are already ‘pre gapped’ meaning no maintenance or measurements are required.

As once they have reached the end of their life it is relatively simple and inexpensive to replace with another pre gapped spark plug.

Although it can be done, it is not advised to clean spark plugs either. An old plug does not have sharp edges as they have been worn down.

This could result in a less efficient spark and therefore combustion in your cylinder block. It is much better to simply replace your plugs, especially in performance applications.

How do you fit a spark plug?

Spark plugs may be easily installed. Make sure you have the right equipment before you begin. Locate the ignition lines that lead to the engine's core.

You'll need a spark plug wrench, typically much deeper than a socket set to house the plug casing, and choose the correct size or you risk burring off the nut, or mis threading the plug when fitting it.

You'll need a set of plugs, one for each cylinder, so for a 4 cylinder engine you'll need 4 plugs.

Other engine arrangements, such as a V6 with two banks of 3, may be found in certain vehicles, although most automobiles have four cylinders. A single lead for each cylinder's spark plug will be present regardless of the design.

On some engines the plug lead houses the ignition coil- the bit that amplifies the power to cause a spark, on typically older engines one coil is present and this high tension current is carried by the plugs. BE CAREFUL AS YOU ARE DEALING WITH QUITE HIGH VOLTAGES HERE.

Step by step guide to replacing spark plugs

  1. The engine cover may need to be removed. Plastic is the most common material, and they may be attached in one of two ways: by screw or clip.
  2. Changing the plugs one at a time prevents the leads from becoming jumbled up. This would cause the spark plugs to ignite in the incorrect sequence, resulting in engine damage.
  3. Remove the first plug from the socket using the removal tool. Your engine's health may be gauged by looking at the condition of the spark plugs. For further examination, arrange them such that they may be removed in the sequence in which they were placed.
  4. It is critical that new spark plugs be installed straight when they are first installed. For the time being, merely screw it in as far as the plug will go with your fingers still on it. The plug tip may be readily reached with your fingers in some engines, but the tool may be necessary in others; if so, hold it like a pencil and avoid using leverage at first.
  5. In the beginning, do not tighten any farther than a finger's width. Once you've gotten it as tight as you can with your fingers, use the plug tool to further tighten it.
  6. Cross-threading the plugs will cause damage to the engine block since it is softer than the plugs. They need to be straight for this reason. (In most cases, you can repair a cross-threaded spark plug using a helicoil or re-cutting the thread but damage can sometimes be quite costly to resolve.)
  7. Repeat the procedure with the next plug. Examine the old plugs once you've replaced all of the new ones.

You can tell whether your engine is operating at an optimal level by looking at its colour, a light grey is healthy, oily soot is not in most cases!

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