Spark Plug Protrusion into Head?

[Tim Ayers]

Originally Posted by Bored&Stroked

In NGKs, I don't like to run a heat range of '4' (a bit too hot for me) - much prefer a '6' for a performance street engine. NGK has a whole host of .750 reach plugs - with various electrode designs, heat ranges, different materials/cores, etc. You might checkout the NGK 7910 - which is a heat range of 6. Another number that I used to use is a B6ES . . . which can be cross-referenced to a lot of different plugs.

Another option is a R5671A-7 - which is a racing plug, but it is in a heat range of '7' - which is a bit cooler - though their racing plugs don't come much hotter than this (for obvious reasons).

Keep in mind the nomenclature for NGK is backwards from Champion (when it comes to heat range). The lower the number, the hotter for NGK.

Thanks, Dale. I've got .750" extended reach 4's & 6's coming in. I'll start with the 6's and see how they do.