Gap is a distance between center and ground electrodes. Bigger gap creates bigger spark, which ignite more fuel. On the other hand, bigger spark is harder to occur and has more chances to misfire. That’s why it’s important to stick to OE gap sizes.
Thread diameter and pitch are fundamental dimensions. You physically aren’t able to fit spark plug with another thread, so check it in a first place.
This parameter indicates how well spark plug transfer heat from the engine. Some engines produce more heat (i.e. race engines), some less, but all spark plugs should operate in same temperatures: from 500°C and below 950°C.
Since all manufacturers have their own heat ranges, we’ve unified all of them to NGK’s chart: heat range “14 (4)” means 14 is the brand’s heat range and 4 is NGK’s equivalent.
Note: E3 and Autolite cannot be referenced by heat range.
Reach is a distance between spark plug seat and the end of a thread. If it will be too short, spark will occur outside the combustion chamber; too long – it’ll collide with the piston. So it’s crucial to follow the OE dimentions.
Occurring of a spark plug is followed with another event – radio frequency interference (RFI). RFI creates a static electricity, that can accumulate and discharge on car’s electronics and destroy it. Resistor surpress RFI and saves your electronics.
If your car from factory has spark plugs with resistor, use only resisted spark plugs. If you have an older car with little of electronics, you can use both resistor and non-resistor spark plugs.
All materials works the same. They differ by the durability in following order (first the strongest):
This means you can choose any material as long as spark plugs fits by other parameters, yet it’s recommended to use more durable materials since they decrease chances of misfires.
For this relationship we use official documentation from manufacturers, like this one:
Using it we get a match-list and form tier 1 relations (A = B, B = C). Then we form tier 2 relations: if A is a replacement for B, and B equals to C, then A and C are also can be referenced (A = B = C). That way we reference all plugs from several manufacturers’ charts to make a most comprehensive cross-reference table for spark plugs.
While cross-reference table is formed from manufacturer’s charts, this table we make based on our data.
Each spark plug has its own set of characteristics. Similar spark plugs are those which characteristics are fully or closely corresponding to each other.
First of all, we make sure that spark plug will fit the engine by the thread diameter, thread pitch, hex size and reach. If any of those parameters differ, the spark plug cannot be installed.
Secondly, we ensure that spark plug is designed for the same engine condition: has the same heat range, gap, projection, resistor. For more information, check our spark plugs guide. The two things that can differ are materials and electrode design, since they are interchangeable.
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