Spark Plugs

Which spark plug does your engine need after you have increased boost pressure or compression? Here we bring together spark plugs for petrol engines in both standard and racing versions, with different heat ranges and electrode materials, for you who want stable ignition in your project.

What the spark plug does in a tuned engine

The spark plug must produce a stable spark on every power stroke, even as cylinder pressure rises. With higher boost or compression, the spark typically requires more voltage, and too large an electrode gap can cause misfires under load. At the same time, the spark plug must dissipate heat: a plug that is too hot can, in the worst case, trigger pre-ignition, while a plug that is too cold can foul up with a lot of city driving.

How to choose spark plugs

Start with the specification for your car or engine, and then consider these points:

• Heat range: More power typically calls for a colder plug. Note that the numbering does not follow the same scale with all manufacturers – the HKS M series, for example, is available in heat ranges 8 and 9.
• Electrode material: Iridium and platinum typically wear more slowly than nickel, but service life depends on the engine and driving. From NGK, for example, there is a single-platinum plug (BKR6EGP).
• Electrode gap: With boost, a smaller gap is typically recommended; follow the instructions for your engine and your tune.
• Thread and reach: Thread diameter, length and seat type must match the cylinder head.

Installation and maintenance

Install spark plugs in a cold engine and tighten to the specified torque, as both too loose and too tight can damage the threads or the seal. Check the electrode gap before installation. The deposits on a used plug can give a hint about the mixture and heat range. In addition to spark plugs from NGK and HKS, we also stock parts from Moroso, Ford Racing and OMIX. For diesel engines, take a look at glow plugs instead.

Frequently asked questions

Should I switch to colder spark plugs after tuning?

Often yes, if power or boost has been increased significantly, but it depends on the engine, fuel and driving. One step colder is a typical starting point, and the deposits on the plugs can show whether the choice is right.

What is the difference between iridium and platinum spark plugs?

Both materials are hard and typically wear slowly, so the replacement interval can be longer than with nickel. Iridium often allows a thinner centre electrode. Which one suits best depends on the engine's specification and your tune.

Why should the electrode gap be checked before installation?

The factory gap does not necessarily suit your particular engine and can change during shipping. At high boost, too large a gap can cause misfires, so measure and adjust according to the instructions if the plug type allows it.