Understanding Viper Spark Plug Codes: A Complete Guide

Viper Spark Plugs

We are pleased to announce that our new Viper spark plugs have hit the shelf. If you’re already familiar with our high-performance Viper coils, you will know that the Viper plugs will be the perfect addition to your ignition system. Viper plugs are built to last, with a choice between copper and iridium electrodes, you can now get the perfect set of plugs to go with the rest of your ignition set-up. But which ones do you need?

We’ve based our product codes on the NGK codes so that finding the correct one is easy. The only difference between the Viper and NGK codes is the starting letter. We use ‘P’ at the start instead of ‘B’, which is the most common size of plug. This means that if you know what NGK plug your vehicle takes – as specified in your owner’s manual – then you know which Viper plug to upgrade to. Our fantastic iridium range follow the same system, they start with an ‘I’ instead, with the rest of the code the same as the equivalent NGK code.

Spending more than £85? You can get yourself a free set of plugs with the code VIPERFREE25 (offer ends 31st Jan 2025) enter this coupon at the end of checkout to receive the offer

Viper Iridium

Iridium plugs can facilitate the spark more efficiently than conventional copper plugs. The higher conductivity of the iridium alloy electrode makes the spark more concentrated, meaning less energy loss and improved efficiency. As a material, iridium is also very tough and more resistant to heat, meaning your plugs will last longer. So, for better efficiency and durability, you may want to consider switching to Viper iridium.

Properties of Spark Plugs

Each spark plug variant has several unique and distinctive properties, as labelled by their code, and it’s important to match these to your engine, so let’s take a look at the chart below and we will go through each character in order:

1. Shell: The first character of the code, representing the shell, simply denotes the size of the thread that screws into the engine block and the size of the hex socket required to remove it. For instance, a shell code of ‘B’ will be a plug with 14mm x 1.25mm with a 13/16” hex, a highly common and standard size for most classic cars.
2. Construction: The second character (and sometimes third as well) tells you the construction, which gives you an indication of the design of the plug. For instance, ‘P’ means the plug has a projected tip, a design where the central electrode and insulator extend slightly beyond the end of the threaded shell, meaning the spark is delivered deeper into the combustion chamber. Your owner’s manual will tell you whether you need a specific construction. There may not be a specific construction required, in which case you could fit something like a ‘P6ES’, where no character in position 2 is specified.
3. Heat Range: The numerical heat range of a spark plug refers to its ability to dissipate heat. It is an essential factor in ensuring efficient engine performance and avoiding issues like carbon fouling or overheating. NGK and Viper use a numbering system to represent heat range, with lower numbers indicating hotter plugs and higher numbers indicating colder ones. This rating is influenced by several structural elements of the plug. Insulator Nose Length: A longer insulator nose retains heat, making the plug hotter, while a shorter nose dissipates heat more effectively, resulting in a colder plug. Material Properties: The thermal conductivity of the insulator and electrode materials plays a significant role in how heat is transferred away from the spark plug. Design Factors: Features such as copper cores and the structure of electrodes are engineered to optimize heat flow and performance. To function optimally, spark plugs should maintain firing end temperatures between 500°C and 800°C. Operating below 450°C risks carbon fouling, while exceeding 800°C may lead to overheating and engine damage.
4. Reach: The reach of the plug is the length of the thread, indicated by the fourth character. Again, this will be specified in the owner’s manual.
5. Firing End Construction: The final one or two alphabetical characters gives you the design properties of the firing end, and there are a lot of different types. The main one that you’ll see in Viper and NGK are ‘S’, which is means there is a 2.5mm copper electrode – standard issue for many manufacturers, and ‘T’ which means 3 hybrid ground electrodes – this means that there are 2 smaller electrodes either side of the main one so that when the main one experiences carbon fouling, the spark doesn’t suffer, and then the main electrode returns to normal when the carbon is burnt off.
6. Gap: For the most part, these are pre-set and not specified in the plug’s code, but they can be adjusted if needs be. A gap too small can lead to a weak spark, while a gap too large may cause misfires, especially at high RPMs. Always check the gap of new spark plugs before installing them using a feeler gauge to ensure they are within the manufacturer’s recommended range.

Now that you know what your spark plug codes mean, you should be able to make a good choice when it comes to which Viper plug to fit to your car. If you’re not sure you can always ask us. We will have more articles in the future about some of the conditions which affect spark plugs and some common issues, along with some of the ways in which they can indicate other potentially dangerous or damaging problems with your engine.