After doing some searching and not really getting clear answers I decided to make a little write up so that future people don't have to look for this info like I did. (Sticky??)
Here's what I've found for what type
of plugs you need for running nitrous:
(BTW- this info goes for all engines makes and models)
Try to avoid platinum (particularly double platinum) plugs. There are suggestions that a chemical reaction may occur and some unusual deposits will form on the electrodes - these may impede ignition performance. Double platinum plugs (where a platinum 'chip' is welded into the ground electrode) may be at risk from the platinum chip becoming detached in extreme temperatures, the surrounding electrode material will doubtless have a lower melting point. A platinum chip dropping into the combustion chamber could be disastrous.
Try to find a plug with a short ground electrode. This is generally thought to be more important than a colder heat range. Because temperature will increase so severely and quickly when using nitrous oxide, the temperature at the tip of the plug's ground electrode will become extremely hot very quickly - the longer the ground electrode, the longer it will take for the excess heat to be conducted away from the tip to the plug shell and ultimately into the cooling system. An overheated ground electrode tip can cause detonation and may even fail completely.
Try to find a 'non projected' plug. The design of a projected plug will usually aid ignition performance at low engine speeds by moving the spark position closer to the centre of the combustion chamber, the downside of this is that the center electrode and central ceramic insulator become exposed to combustion gases and hence are at risk of damage under extreme conditions. By using a non projected or even a retracted spark position, the firing tip is more protected and plug failure is less likely. A non projected or retracted plug by design will have a shorter ground electrode which is beneficial for the reasons mentioned in 2. above.
Use a non resistor or Iridium type plug if available. Please note if your vehicle manufacturer recommends a resistorised plug as standard we would not recommend using a non resistor plug, interference with engine and safety management systems may result! Some plug designs are only available with integral resistors. By using a non resistorised type plug, the amount of voltage available at the plug's firing end is slightly increased and therefore the risk of misfire under load is reduced. If combustion conditions are particularly extreme then an increased 'spark jump' voltage is required. Effectively, when more fuel and oxygen are compressed in the combustion chamber (as occurs in nitrous/turbo/supercharger use) the result will be similar to that of increasing the plug gap - if the gap becomes too large for the available voltage then the spark simply won't be able to jump the gap. Iridium spark plugs can help as they have a greatly reduced firing voltage (despite an integral resistor) - lower overall than most copper non resistor plugs. High performance ignition leads (such as Magnecor KV85 leads) can also help supply maximum available voltage to the plug.
Use a colder heat range plug. While colder plugs will be of limited worth during a large, short burst of nitrous, they will help to return the sparkplug tip to a safer operating temperature more quickly in between or after nitrous use. The intense heat of nitrous burn will not have time to be dissipated much more effectively by a colder plug in the usually short space of time for which nitrous is injected. A short ground electrode is more useful for maintaining 'safe' conditions during nitrous use (see 2. above)
Ideally you would have a set of standard plugs for daily driving and change to a set of 'safer' plugs for extreme use such as track days/racing etc. This rarely happens so a trade off between daily driveability and high performance/engine safety is required.
info provided by Sparkplugs Limited
This is what you need to know about Heat Ranges
The term spark plug heat range refers to the speed with which the plug can transfer heat from the combustion chamber to the engine head. Whether the plug is to be installed in a boat, lawnmower or racecar, it has been found the optimum combustion chamber temperature for gasoline engines is between 500°C–850°C. When it is within that range it is cool enough to avoid pre-ignition and plug tip overheating (which can cause engine damage), while still hot enough to burn off combustion deposits which cause fouling.
The spark plug can help maintain the optimum combustion chamber temperature. The primary method used to do this is by altering the internal length of the core nose, in addition, the alloy compositions in the electrodes can be changed. This means you may not be able to visually tell a difference between heat ranges. When a spark plug is referred to as a “cold plug”, it is one that transfers heat rapidly from the firing tip into the engine head, which keeps the firing tip cooler. A “hot plug” has a much slower rate of heat transfer, which keeps the firing tip hotter.
An unaltered engine will run within the optimum operating range straight from the manufacturer, but if you make modifications such as a turbo, supercharger, increase compression, timing changes, use of alternate racing fuels, or sustained use of nitrous oxide, these can alter the plug tip temperature and may necessitate a colder plug. A rule of thumb is, one heat range colder per modification or one heat range colder for every 75–100hp you increase. In identical spark plug types, the difference from one full heat range to the next is the ability to remove 70°C to 100°C from the combustion chamber.
The heat range numbers used by spark plug manufacturers are not universal, by that we mean, a 10 heat range in Champion is not the same as a 10 heat range in NGK nor the same in Autolite. Some manufacturers numbering systems are opposite the other, for domestic manufacturers (Champion, Autolite, Splitfire), the higher the number, the hotter the plug. For Japanese manufacturers (NGK, Denso), the higher the number, the colder the plug.
Do not make spark plug changes at the same time as another engine modification such as injection, carburetion or timing changes as in the event of poor results, it can lead to misleading and inaccurate conclusions (an exception would be when the alternate plugs came as part of a single precalibrated upgrade kit). When making spark plug heat range changes, it is better to err on the side of too cold a plug. The worst thing that can happen from too cold a plug is a fouled spark plug, too hot a spark plug can cause severe engine damage
Also to be noted, in case this is the only info you are reading about nitrous, YOU HAVE TO RUN 92 OCTANE OR HIGHER
Here's what you need in plug specs for an Ecotec (L61):
1 inch reach (25mm is acceptable)
Same as above for the other J engines
except your reach is .708 inch
Keep in mind the normal heat range for our engines (all of em) is "5"
Then just choose one step colder for 75 shots or less. Or two steps colder for 100 shots or higher (which you shouldn't be doing unless you have a built bottom end of pistons & rods).
Glad you enjoyed this bit of clear info.