anybody else having flashbacks to shop class in highschool?

Excellent info! Thanks for taking the time post it all.

I just have one, rather elementary, question; What exactly do they mean when they talk about cooler range plugs and how do they play into the detonation picture?

Rick, here is my understanding of plug temp ranges, Ken will correct me if I'm wrong...

The temperature of a spark plug's firing end must be kept low enough to prevent pre-ignition but high enough to prevent fouling. The spark plug works as a heat sink to transfer heat from the combustion chamber to the motor cooling system. The heat range is a measure of the plug's ability to move this heat.

Heat transfer is determined by several factors. Insulator nose length is the distance from the firing tip of the insulator to the point where the insulator meets the metal housing. Since the insulator tip is the hottest part of the plug, the tip temperature is the main factor for pre-ignition and fouling. Spark plug tip temperature must range between 850-1550 degrees. If temperatures fall below 850 then the tip will not be hot enough to burn off carbon causing the plug to foul and carbon build up in the cylinder. If temperatures are above 1550 the plug will overheat which may cause the the tip to melt. The difference from one heat range to the next is the ability to remove about 175 degrees.

A colder plug has a shorter insulator and a hotter plug has a longer insulator. There are other factors to consider such as fuel/air mixture, compression ratio, forced induction, timing etc when choosing the correct plug.

What say Ken? Sound right?

Rick,
In the May issue of Popular Hot Rodding magazine, there is an article, 'The Secret Life of Spark Plugs' that is a 'must read' for the do-it-yourself tuner uppers.

Owen, very good. You got heat range right on the nose. But once again I'm going to add a bit. In addition to heat range, you need to consider spark temp.
Spark temp and heat range are two different things. Spark temp is the actual temp of the spark jumping the gap. This is what actually lights the fuel. First I will stress the heat range must be correct for this to work properly. If the spark temp is too low it won't properly light fuel. If it is too hot it is usually too short, and may require a lower heat range to stop from overheating the plug.

Spark temp is controlled by changing the resistance of the secondary ignition, cap to rotor gap, plug wire resistance, and spark plug resistance. If the resistance is higher it takes more energy to start jumping the plug gap. This caused the KV ( 1 kv is 1000 volts) to raise, and causes a higher spark temp. Less resistance jumps the gap easier, resulting in a lower KV and a cooler spark temp.
Now a bit more. A coil only produces so much energy. The more energy used to start the spark, the less left over to maintain the spark. The less required to start the spark across the gap, the more energy left over and the longer it will maintain the spark.
So too cold due to a low KV and low resistance will result in a long duration spark, but it won't be hot enough to light fuel. Too hot from high KV will create a lot of heat to light fuel, but won't last long enough for the fuel to be exposed to the spark, and it won't properly light fuel. Some will be left unburned. You would think once it lights it will burn everything, but due to cylinder flow and quench areas, it won't. You need a balance of time and temp.

Most American mfg (GM AC Delco, Ford Motocraft and Autolite, Chrysler Champion) get most of the secondary resistance in the spark plug. The Europeans (Bosch) get most of the resistance in the wires. The Aisans (NGK, Nippondenso) are in between.
This means if you put Bosch in a Chevrolet you may have a long duration but very cold spark. This can cause misfires or cold and warm driveability problems, I have even seen no start.
Champions in a VW blister the plugs and burn out quickly. Bosch in a Chevy Sprint (aisan car) lost 6 mpg, until the NGK went back in. I can go on with many, many examples.
Unless the engine or ignition has been modified, it's usually best to stick with what the mfg put in there. There are many exceptions. These depend on how and where you drive, and design of the engine, as well as the fuel being used. Sometimes different plugs can be used on purpose to create specfic conditions, and can work very well if planned out, or just plain lucky.
Sometimes plantinum plugs are used due to very good antifouling properties.

Bosch and others often use one platinum plug to cover several different heat ranges. They pick a cold one for several hotter ranges. This would foul a regular plug, but they stay clear. This does not mean they will have the correct spark temp. This can be to your advantange when racing or for other special purpose. It all depends on what you have, and what you are trying to do.

Now for worthless trivia. Albert Champion created Champion Spark Plug Company, did very well, and retired early. Later he wanted to go back to work, and ended up working for GM. He could not use his name on the spark plugs he was creating, so instead they used his initials. AC (Albert Champion) Delco. There you go.

Good work Owen

Ken Styer

so Ken, can you over power the resistance in the plugs by creating to little resistance before them, ie wires, distibutor gaps? how do upgrades in ignition affect the combustion? once again it sounds like more is not always better.