I did some searching and all I found out was that it was bad to use overly cold spark plugs on the street, but I never found out why. What are the drawbacks of using NGK 13's or any other cold spark plug on the street? What about the pros?

 

First of all, do you know how much those things cost???
They are like $30+ EACH!

Second, overly cold spark plugs cannot get up to proper operating temps, cause they are too busy conducting heat into the rest of the engine (from the spark plug threads).
If they spark plug doesn't reach the proper operating temperature, they tend to foul.

Heat range 13's are about as cold as you can go, and I would be surprised if those things were able to crank, idle, and stay idling more than 5 minutes...or even driving around for the initial 5 minutes.
Once they foul, the engine runs badly...and then stalls.
It will not start.

On the other extreme, too hot of a heat range will cause the spark plug to "overheat".
Too hot of a spark plug will cause it to errode prematurely.
Too hot of a spark plugs can cause pinging and detonation, causing the firing electrode to turn red hot and end up igniting any fuel mixture that comes in contact with it...at the wrong time!
That is bad bad bad!

So, stick with recommended heat ranges unless you're racing which might justify colder spark plugs.


-Ted

 

Thanks, so I guess 9's, possibly 10's would be the best for a street/circuit FC

 

Even 10's (actually 10.5's) are too cold for street driving.


-Ted

 

hmm i'm using 7's ... is that too hot?

NGK BUR7EQ to be precise..

 

Those are stock recommended heat range plugs for the FC.
Most people can run the 9's in the leadings and get a little bit more life out of them, since the 9's don't erode as quick as the 7's.

If you do a lot of city, stop-n-go driving, stick with the 7's in the leadings.

(I hope you're using 9's in the trailings, cause that's what Mazda recommends???)


-Ted

 

Someone please elaborate on this topic! I replaced my spark plugs and I thought they were all the same. I figure all 4 are identical.

 

nope. there is a trailing and leading plug for each rotor (trailing on top, leading on the bottom). i dont know the specifics on what the difference is between them, but theyre def not all the same.

 

Could be the length of the electrode, cause I know that the trailing holes are deeper than the leading or someshit, can't remember.

 

Thanks for the info. I replaced mine about 1 1/2 weeks ago, and the previous plugs were not only all leading, but 9's. I just put in 7 lead, 9 trail, and what a difference. Listen to RETed, knows his shi t, (stuff). Thanks.