spark plug question: stockish FD... why have HOTTER plug in LEADING
 

I was just thinking about this because I am going to change my plugs. The OE spec calls for BUR7EQ's (P for the platinum folks) in leading and BUR9EQ's in trailing. From what I understand, the 7's are a HOTTER plug and the 9's are colder. Why, for detonation supression sake, would Mazda run a hotter plug on the leading side of the chamber and a colder one on the trailing side? That seems more dangerous to me. I've read some threads which indicate that idle quality and plug life is comprimised with colder plugs; perhaps that is part of the reason.

I know that the timing split influences chamber pressure (and probability of detonation), so perhaps running a colder plug trailing with less split will give decent power and some margin on detonation due to colder trailing plug... although IIRC, stock split @ 10 or so psi is around 14 degrees which seems to be conservative from what I understand.

Any ideas or is this just a waste of time :) I think next time I think I'll just run 9's all around. Mods in my sig. What do you guys think? Also, any fresh ideas on the worth of running platinum VS. non platinum plugs, for a "mildly" modded car (like my own)? The consensus appears to say that platinum plugs are a waste.

Thanks in advance.

run all 9s unless you are bone stock, 9s may foul in a bone stock, casually driven car

I run the Denso iridiums and love them

^^ What's the part number/plug designation? Thanks :)

http://www.densoproducts.com/results...ctCategoryID=1

Denso Tech Line (888) 963-3676

NGK Tech Line (877) 473-6767

Equivalent Heat Ranges
NGK Denso
8 - 24
9 - 27
10 - 31
11 - 34

I'm running 27s...rule of thumb is drop one heat range every 50-75 hp over stock

The reason for running a hotter range plug on the leading side is to burn off the deposits that inevitably form on the insulator and electrode from the intake charge not burning completely, especially at idle (another inevitable occurrence with the rotary's rectangular combustion chamber). If the plug range isn't hot enough for the conditions (your engine's state of tune, how you run it, etc.), those deposits will collect and can eventually render the spark plug useless (i.e., foul it by preventing the formation of the electrical arc).

The trailing plug is mostly for "cleanup" purposes of the combustion cycle, helping propagate a flame front to progress across the length of the rectangular combustion chamber. Since it doesn't come in contact with the amount of fresh intake charge that the leading plug does, it doesn't need to be as high of a heat range to burn off deposits.

And it *does* also help to draw some amounts of heat from in the engine... Spark plugs server two purposes one (and the more widely acknowledged one) is to provide the spark necessary for combustion, and two is to draw heat from the combustion chamber.

You don't want to draw heat from the combustion chamber because that energy is what drives the internals. What you're probably referring to is that a colder heat range plug transfers heat from the firing tip more quickly to avoid heat saturation that could cause pre-ignition. The trailing plug lives in a higher temp environment compared to the leading plug because it's always firing in a charge that's already burning.

^ You, sir, are a much smarter man than I. Lol, I must have misunderstood when I was skimming through the NGK site.

Makes sense =)

he's not only smarter, he's alot faster :)

too bad we can't get an early review of the 2009 R1 ;)