So what are these things ? Spark plugs generate the spark obviously :\ but where?
In your engine cylinders, you have a huge air fuel mixture coming in from the intake and it somehow has to ignite to produce a downward displacement force on the upper surface of the piston to generate crankshaft movement. The spark comes from a voltage driving the spark between that tiny gap on the end of the plug. You can get the gist of it from this:
Now let’s look at those people who want to strap turbos to their non-turbo cars (I’m gonna have heaps of junk later which is related to this :D). Since turbos cram more air into your cylinder, it essentially resists the spark jump across the gap which means, a higher voltage is required. Not only that, high voltages need to be insulated in that space before the gap so your entire engine doesn’t collect charge.
To those who look to low boost pressures (under 10 psi), your system should boast enough voltage to get good sparking going on. Higher boost applications mean you’d have to install this thing called a capacitor discharge ignition supplement to increase the voltage capability.
Now, onto spark plug choice. Those who usually give a rat’s a** about it and just choose the pretty looking ones are known as the tyre kicker variety. It’s rather simple to choose and here’s how:
Obviously, if you’re going to be driving with a denser mix of air and fuel from the turbo, there’s going to be loads more heat being transferred into the plug. In a nutshell, there are two types of plugs: cold plugs and hot plugs. A cold plug conducts heat VERY quickly and well whereas the hot plug conducts heat away slowly. Logically, you’d jump onto the cold plug choice but it’s not always the best answer since you’d actually want balance. Let me explain:
Ideally, the best plug would operate in a range hot enough to burn off any kind of build up residue on it but cool enough to prevent a rapid breakdown of the plug itself. Also, if the plug itself is too hot, it can ignite the fuel air mix before the spark is even made (This is known as pre-ignition or DETONATION: A BIG NO NO if you want your car to remain running).
Great plugs also depend on how they’re installed i.e. some idiot installing them without the love will have a poor running setup. Get some respectable lube (hehehe) or anti-seize compound onto the threads before installing and tighten to the specified torque value provided in your service manual.