[Alan Roehrich]

Of note, the AC Rapidfire is a "broad heat range" plug, they're designed to heat up fast and clean off, without getting too hot. Back when they were first introduced, the AC rep who taught the classes I mentioned in a previous post gave us plenty of back ground on them. This may in fact be a really good thing for a race car, considering the amount of time they spend idling and at low speed, as well as being started relatively cold. Add to that the fact that a lot of people set their idle mixture fairly rich, and you can see where a plug with the design attributes of the Rapidfire might help. Having used them in various applications over the years, I'm not convinced the current version is as good as the original version of several years ago. I have however seen them last as long as or longer than the high dollar "precious metal" plugs, and perform as well or better, in many applications.

Smokey Yunick once told me "if you knew how many times your engine actually misfired, you'd be so pissed off, you'd never start it again". What a lot of people don't understand is that most of the noise you hear is from air flow, not actual combustion. Yes, you can hear a dead cylinder easily. But as Smokey once demonstrated, and backed up with data, what you can't hear is how often each cylinder has a partial misfire. I don't think you can solve that problem with trick spark plugs, or trick spark plug wires. I do think you can make the problem worse with the wrong spark plugs. I don't think any one company makes the best plug, or the best plug for all applications.

It should be understood that most of the "precious metal" content in spark plugs is not for more, hotter, or better spark, but rather for longevity, allowing the OE to reach closer to the unrealistic "100K mile spark plug" that is pretty much required by the current emissions standard. It should also be understood that while the "100K mile without a tune up" is a good marketing ploy, what it actually means is that the "tune up" will merely meet the emissions standard at 100K miles. It does not mean that the parts are actually giving you the best performance and economy for 100K miles. They are not. They start to really degrade past 50K. Even if the plugs do not show severe gap erosion, they will show significant build up of deposits.

Odds are, long before you see any of the actual advantages of the "precious metal" plugs, you'll have swapped them out for fouling, deposits, or just habit.

The above is sort of a long way of saying I'm not sure you'll see much of a gain with expensive "precious metal" spark plugs in most race engines. There may be the odd application where you do. However, if you have a good hot ignition system and top quality plug wires, a good set of copper core spark plugs (with the resistor) is probably good enough. Without that resistor, you can end up with "noise" that can cause high end ignition systems (MSD, ICE, etc) to have odd behavior. It could leave you chasing a misfire or flutter for quite a while.

Last, there can be some gains to the "fine wire" center electrode. They warm up fast, and they tend to concentrate the spark kernel.

The rest of the trick stuff, multiple ground electrodes, trick ground electrodes, trick center electrode tips, don't seem to show any gains, and often show losses.