spark plugs, GT vs ST Options

[Hanyo]

yet another spark plugs question.


Just did a service on my celica today and took out the spark plugs.

The old spark plugs look great considering they have been in there for around 50k miles.



Seeing the great wear I am getting on those denso plugs; I decided to put the exact same plugs in there. The car starts fine and is silky smooth now.


The problem came up when I did some further research on these plugs; They turned out to be one heat range hotter then the stock OEM spark plugs. Further detective works revealed they where designed for the 5sfe engine.

So here is the question:

Who else runs a hotter spark plugs in their 7afe? My main concern is I fill up with 87 California gasoline which has the worst octane rating compared to the other states and detonation could be a problem.

So should I toss these spark plugs out and put in the right heat range? Or should I set it and forget it considering they ran well for the 50k miles that I put on them?

[Hanyo]

They look great and look like the correct heat range.
How did you determine that they were the wrong range?

I look them up through cross referencing them and using an application chart.
7afe spark plug
5sfe spark plug

What really throws me off is how good they look even though they are the wrong heat range. On the other side of the spark plug you can see the healthy orange/tan discoloration.

Another think I'm not too sure of is denso used the same heat range number system as NGK. Where the higher the number the colder the plug?

The 5sfe calls for PK20R11 where as the 7afe needs PK16R8.
5sfe gap is wider at .044 and the 7afe gap is .028.

I dont know which gap to set it at. I set my gap at .032 per the NGK spark plug chart.