is there a difference between what type of plug needs to be in the leading spot vs. what type needs to be in the trailing spot? i recently purchased a "set" from rx7store.net and they both have the two blue rings with the "T" for trailing mark on them. what do i do now? i thought it was supposed to be marked L for leading and T for trailing.

 

If you have modifications, it's better to run all four trailing plugs anyway. It's perfectly safe and many of the forum members do it, including myself.

 

you are correct the L is for leading the T is for trailing. L plugs go on the bottom and T plugs go on the top

 

you sure about that rynberg? sorry to second guess like that... i guess i'd feel better if i knew what the difference was. could you explain that to me?

 

The heat range for the stock leading is 7, the heat range for the stock trailing is 9. As you add modifications to the car, the 7 heat range will not be able to withstand the increased power the engine is making and therefore running a 9 heat range helps out. The higher heat range can mean that the plug will foul faster in stop-and-go driving and may have a rougher cold idle. To be honest, I didn't notice any difference going from 7 to a 9 plug. I'm waiting to see if they hold up better (stock plugs last 12k miles or less).

 

ok, thanks very much, i appreciate it... sorry to everyone about the double post... it was a total accident

 

Ideally, the idea isn't to notice a difference. The difference you could possible notice, is when you blow an apex seal due to your plugs getting warmed up and firing off the timing pattern.

It is very difficult to say what caused an exact detonation some times. This is just another way to assist in preventing that outcome.