Question about Spark Plugs BR4HS Plug 10/BX #3322
The numbers 4 and 8 are heat ratings. The lower numbers run hotter. Different heat ratings allow you to choose the best compromise between keeping the plug from fouling and making the electrode last longer. If your plugs tend to foul, you need a hotter plug. If they tend to fry away, you need a cooler one. As engines get old, they tend to need hotter plugs. The differences in the heat ratings can be seen in subtle differences in the dimensions of the electrode (usually the center one) and the little insulator around the center electrode. The dimensional changes effect the heat transfer characteristics of the plugs, which changes how effectively the high temperatures present at the spark are conducted away. Besides the heat rating of the plug, the other big factor is having a nice clean thread surface in the engine block, which is why some mechanics will use a thread chaser when changing plugs. Here's a link to NGK's numbering meanings
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Posted on Aug 27, 2010
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Posted on Jan 02, 2017
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