[Quijinn]

Ok you all are both right to a degree. A spark plug heat range is simply this, how fast can it move the absorbed heat into the head. It absorbs heat because it protrudes into a 1500 degree oven so given enough time the plug will rise to 1500 degrees. By haveing more internal contact area, the plug can pull the heat it absorbs and displace it into the head. To get hot it has to absorb to cool it has to displace. The colder the plug, the more heat it can displace before it starts to glow, thereby pulling heat from the combustion chamber.

Ok now remeber the 1500 degree number being toss around is only at and around peak torq rpm and only during the 0-15* ATDC in normal burn so the rest of the time the rings, combustion chamber, and cylender walls are releasing heat into the coolant, also so is the plugs. The plugs are now trying to cool back down due to the contact area of aluminum so as the coolant pulls the heat away The plug is still in the chamber absorbing some heat. given not as much as the walls but more then the piston rings, more contact area with the head.

During the duration of the flame font the plug is heating up, just like everything else, it can only do this if it is in the heat area. Plus you should look at this, the center of the combustion chamber is the hottest part, the outter rim is cooler because of the coolant to help control detonation. A hot plug will glow because it cant disipate heat fast enough and preignite, it can also cause detonation......

Anything that can start a 2nd font will cause detention, gas's are not sitting there wating there moveing, so as gas moves over a hot plug it can cause a 2nd flame font. Cooler plugs can help with detination, but it can help more with preignition and preignition caused by detination. Detination heats up the plug, the plug glows and preignites the fuel. Colder plug will resist this much more, by releaseing the heat into the head.


My $.02