What the difference between different spark plugs temps when it comes to the ngk's? Also when you gap a plug wider or smaller what's the difference and when should you use different ones?

 

The purpose of going to a colder plug is to prevent pre-ignition or engine knocking in I high performance engine. The plug is made of materials that can better expel heat. It pretty much depends on the temperatures inside the combustion chamber. Using a colder plug on a stock or mildly modified engine is not usually recommended because the plugs will not be able to clean themselves and can lead to misfires and a gummed up combustion chamber etc.
With gaping, the basic rule of thumb is the wider the gap, the stronger and more powerful the spark, but the more odds of the plug not to fire all together at high rpm (or even low), Hence why the gap got changed from .060" on the LS1 to .040". And its the opposite for a shorter gap. The shorter gap is more dependable and gives that smooth idle. But the spark is weak because the coils do not have time to build up before the current jumps the small gap of the plug.
For your everyday average joe driver, going with the shorter end of the manufacturers recommended gap range is a good way to go. This will give a smoother idle, less misfires, and keep most people happy.

I believe you should try to get the largest gap possible while maintaining a smooth idle and not experiencing misfires at WOT.
I run my plugs at .050 currently as it is a great medium between the .040 smoothness, and the larger more powerful and complete burn from a plug with a larger gap like .060".
It is also said that a larger gap burns the A/F mixture more clean. So it can help come emission time. But this will not help if there are misfires from going to large!

 

Running a colder temp plug is typically done in cars with forced induction and increased boost. For example on a supercharged vehicle, one might replace the factory supercharger pulley with a smaller sized unit which will increase the supercharger output/boost. Increased pressure means increased temperatures which means increased chance of knock. A colder temperature plug will help prevent pre-detenation or knock.

 

Heat ranges are really determined by the length of the insulator on the plug, not just materials. Different manufacturers have different heat ranges so they are not all the same. You have to look at comparison charts to match them up correctly. NA motors benefit just as much from colder plugs when needed. Technically you go by horsepower increases and compression ratios, not by whether its forced induction or na. Most guys go to a colder range at around 100flywheel hp over stock but it can vary between cars and tunes.

Heres a helpful comparison chart,
http://www.ls1.com/forums/f10/spark-...e-chart-13070/