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For extended use at high engine loads, a heat rating of 5 is advisable \(FR5IX\) with a g\ap of 0.9mm. Heat Rating of a Spark Plug A spark plug must dissipate the heat produced by the combustion gases. Gives the flame an unblocked area to grow creates a larger flame. Allows spark to expand directly above the midpoint of the electrode core preventing the spark from being shrouded by the ground strap. These plugs may be fitted to all earlier cars. ACCEL C-Cut Copper Spark Plugs creates a considerably hotter spark that lets the flame expand more rapidly in the combustion chamber. For the later cars, suitable plugs are BKR4EIX or FR4IX. The only difference is that those cars were delivered with a 16mm hexagona\l fitting rather than the earlier more common 20.8mm type. Note: 1994MY cars and later use plugs of the same rating. Once again, you’ll need a colder heat range to rapidly transfer all that extra heat to the cooling system.As an example, the NGK GR4IX spark plug is now the only plug to use on all SY and SZ cars until Model Year 1994. Increased compression ratio: Higher compression ratios mean higher cylinder pressure and temperature.As a result, you’ll need a colder plug to transfer more heat from the combustion chamber. Methanol: Since it has a higher octane level than standard gasoline, methanol delivers more complete combustion.Nitrous oxide: The high cylinder temperatures caused by nitrous usually requires a colder heat range over the stock plug.Depending on the exact application, you’ll need to go with a significantly colder heat range (faster heat transfer) over stock. Supercharging/turbocharging: Forced induction leads to increased cylinder pressure and temperature, which could lead to detonation.Here are some more basic guidelines to get you pointed in the right direction: Example a R5671A-7 (a good street/strip plug) is a cold plug where a R5671A-10 is a very cold plug used for large 400hp and up nitrous and other power adder applications) Autolite Heat Ranges - The larger the last digit in the part number, the hotter the plug is. Be prepared to supply some basic vehicle information, including any modifications you’ve made.Īs a rule of thumb, you can expect to require one heat range colder than the factory-supplied plugs for every 75-100 horsepower you’ve add with your modifications, according to Champion Spark Plugs. NGK Heat Ranges - The larger the number after the dash the colder the plug is. You’ll need to talk with your sales rep or consult with the manufacturer to find the best heat range for your application and spark plug brand. Before we can get into what heat range plug we recommend you should have a. Unfortunately, heat range numbers are not universal-each brand has its own method for assigning heat ranges. NGK Spark Plugs are a great choice and are recommended by KillerRONS and will. This keeps the spark plug temperature high, which allows the plug to self clean and prevent fouling. Because they have a longer insulator nose length, heat is transferred from the firing tip to the cooling system at slower pace. Conversely, hot plugs are good for applications that operate mainly at low rpms. In broad terms, spark plugs are often referred to as “hot plugs” or “cold plugs.” A cold plug has a shorter insulator nose length-the distance from tip to spark plug shell-and transfers heat rapidly from its firing tip to the cylinder head water jacket.Ĭold plugs are ideal for high rpm engines, forced induction applications, and other instances where the engine produces high operating temperatures. Heat ranges are designated by each spark plug manufacturer with a number. Most spark plug manufacturers recommend that the tip temperature remain between 500° C and 850° C. If it the heat range is too hot, your engine could experience detonation, pre-ignition, or power loss.

If the heat range is too cold, the spark plug will be unable to properly self-clean by burning off carbon deposits. Choosing the right heat range is crucial for high performance engines. Heat range is the speed at which a spark plug can transfer heat from the firing tip to the cylinder head water jacket and into the cooling system.