The Demands of Superchargers, Turbos, and Nitrous
Power-adders do a fantastic job of increasing cylinder pressure and heat. This also places much greater demands on the spark plugs. Nitrous is perhaps the most abusive because of its reputation for extremely fast cylinder-pressure rise time. Some rules of thumb include running a colder heat range and using nonprojected-nose plugs. The general consensus among power-adder tuners is that it's best not to use platinum plugs, since this material acts as a kind of heat sink that will cause pre-ignition problems. Other tips include running a tighter gap, since high cylinder pressures place much greater demands on the ignition system. The best plug gaps are the largest ones that will survive; start with 0.030 inch.
For nitrous, a safe recommendation is one step colder for every 75 to 100hp increase in power. So, for a 300hp engine adding 200hp of nitrous, this would mean using plugs that are two steps colder. This is also a good starting point for similar power increases either normally aspirated or with a supercharger or turbo.
 Our buddy Troy LeCrone tells...  Our buddy Troy LeCrone tells us he tunes his nitrous small-block Chevy with cold AC spark plugs because the ground strap burns easier than with the more durable race plugs. LeCrone views these plugs as having a much quicker "fuse" that will burn more quickly under marginal-lean conditions and perhaps save a head gasket or a piston. Plus, he says, "They're cheaper!" |  High-compression engines that...  High-compression engines that use domed pistons can run into mechanical trouble when the piston domes hit the spark plugs. That's what happened here. This required nonprojected-nose spark plugs that still had to be indexed to place the ground strap away from the piston dome. |  Any engine with high cylinder...  Any engine with high cylinder pressures will generally demand a shorter ground strap, which precludes the use of long-nose-reach spark plugs. The longer ground strap can turn into a heat sink, which can cause serious pre-ignition problems. This is especially true with nitrous. |
 Here's what happens when you...  Here's what happens when you run a too-hot plug in an E85-fueled engine at 12.5:1 compression. E85 is a very pre-ignition-sensitive fuel, and this plug literally melted. On E85, Champion recommends plugs three steps colder than a comparable gasoline heat-range. |  Autolite, Bosch, Champion,...  Autolite, Bosch, Champion, NGK, and others offer race plugs that are generally much colder than production plugs, otherwise they offer little in the way of increased power. These are Bosch race plugs. | |