Spark plug heat range

[Member 10617]

Viv says that he uses and prefers NGK BP5HS spark plugs over Champion. I see that TRF sells NGK BP6HS spark plugs.

I assume that the difference between that "BP5HS" and the "BP6HS" has to do with the spark plug heat range. Viv says he prefers a slightly hotter plug.

Does this mean that the PB5HS is hotter than the BP6HS? In other words, are the NGK plugs "colder" as the number rise?

From what I have learned, if you drive your car short distances at relatively low speeds, a hotter plug is better than a colder plug. Higher speed and longer drives justify a colder plug.

Any thoughts?

 

[Dale]

Lower number is hotter on NGK. Other way around on Champions. I don't like trying to tune with heat range. If everything else is right, the factory recommendation should work all around. I do like the newer tiny electrode plugs as they tend to be less prone to fouling. Especially since my carbs are old and out of tune.

 

[Member 10617]

Dale,

Thanks. That's what it looked like to me, but I couldn't be sure.

Since TRF only sells NGK BP6HS, I take it this would be considered "factory recommendation." I am assuming, however, that no harm will come to the engine if I bump it up a bit to NGK BP5HS... and perhaps it will perform better the way I drive my car (short distances, slow speed).

 

[Geo Hahn]

How to Read an NGK Plug

<span style="font-style: italic">Oh, seems to be a typo on that chart as clearly a plug with a 1.5" reach would be uncomfortable.</span>

 

[Member 10617]

Hi George,

As far as I can find, the NGK BP5HS has a reach of 12.7 mm (1/2 inch) and the NGK PB5HS also has a reach of 1/2 inch. Both have a 14mm thread. This would make them equivalent, I assume, except for the 5 being a little hotter than the 6.

The 1.5 inch reach must be a typo. In fact, that chart is very hard to interpret because it doesn't include the "P" and the "S" in the designations.