I checked the spark plugs today and came up with something confusing...at least for me. I need to replace one.

This is what HKS lists with the part numbers that are on the plugs:
5408-R55RE MAZDA RX-7 (Trailing) 1986-1988 heat range (11)
I have these installed for leading


5408-R525RE MAZDA RX-7 (Trailing) 1989-1995 heat range (10.5)
and these for trailing

These plugs were in the car when I purchased it. They are HKS S series super racing spark plugs. The motor is ported. Is this ok? HKS lists another plug for '89-'95 rx7 with heat range being at (9) instead of (11). What would be the reason fo going for a higher heat range?

 

If HKS is following NGK's convention (colder plugs are listed with higher numbers) then you've got colder plugs, which is good expecially if you're running increased boost.


There have been some interesting threads about spark plug heat ranges on these forums, search around and see what you can find.

-s-

 

wait i tho lower numbers were better and colder?? man just when i think i get it

 

Here's some articles on spark plugs and heat ranges.

The shorter the insulator, the colder the plug.
With NGK (and others) the lower the number, the hotter the plug.

http://www.forparts.com/techngkplugrange.htm
http://en.wikipedia.org/wiki/Spark_plug

Here is the NGK FAQ: Click on "How do I find a hotter or colder plug?"

http://ngk.com/faqmain.asp