Cold or hot spark plug for L-head six engines?

[Fernando Mendes]

I would like to know if the spark plug hot or cold have relation with compression ratio.I always used NGK B6S and after milled its head a friend recommended to use NGK B4.Could this be a increased of compression ratio and it is causing a little leak in the gasket?

[Plymouthy Adams]

ask your friend to explain the B4 an why it is the better choice wand what he based it on.....ask 10 people...get 10 different answers....I really suggest you read a white paper on spark plug heat ranges and the need and why of their difference....

[Don Coatney]

[Radarsonwheels]

After running the motor driving around like normal pull a couple plugs. If it’s not too rich (black) or too lean (white) you should be able to see some color on the electrode strap- the rainbow that is left from heating up steel. 

 

You want that heat mark to be centered around the 90° bend in the electrode strap. Farther down toward the threads it is getting too hot, closer to the tip and it’s too cold of a plug. 

 

There is probably a pretty wide range of plugs that will work fine without noticing much difference in performance or maintenance intervals. When you get into high compression, forced induction, nitrous, and the like you will start needing a colder plug to avoid preignition or putting too much demand on the ignition trying to spark under more difficult circumstances. You can also run a slightly hotter plug as a bandaid for a rich mixture to delay plug fouling but of course that’s not the right way to fix that. 

 

Good luck!

radar

[MarkAubuchon]

I will say plugs do and will make a difference. Used Champion originally switched to auto light much better longevity