Le Mans: Prototype Class
Join Date: Feb 2008
Location: The Georgian Triangle
Re: Spark Plugs
I've read a few posts here and there about copper core plugs being better in highly boosted engines. Platinum and especially iridium center electrodes are pretty hard, which is why the plugs last so long - the electrodes don't erode. In highly boosted engines you are more likely to see pre-ignition and/or detonation, different phenomena with different causes but the end result is the same - high pressure shock waves in the combustion chamber which can break the harder, but more brittle, and very thin welded tips off the center electrodes on platinum and iridium plugs, resulting in mis-fire. The bigger, more ductile one piece center electrodes on traditional copper core plugs stand up better to this sort of thing.
Of course the electrodes on copper plugs do erode, and do so in boosted engines more quickly than they will in NA engines. But this results in a gradual decline in performance, not a catastrophic (for the spark plug) failure which makes it suddenly stop working altogether. In a stock NA engine either type of plug will work. Copper core plugs are cheaper but you need to replace them more often. I'm sure over the life of the car the total cost is pretty close but with iridiums you don't have to change them every year so that saves some work, even if the long term $$ cost is the same.
I've tried all sorts of weird and wonderful miracle spark plugs in different engines. I've learned it is best to stick with what works. For modified engines you may need to try a colder heat range or, in fairly extreme cases a different type of center electrode, maybe more or less extended, maybe even a recessed "racing" type plug but you've got to make some pretty significant changes in the combustion environment before you need to worry about how tip design come into play. If your stock car has run fine with stock plugs for 3 years I cannot imagine you will see any improvement from switching to a different plug. There may (probably?) will be a noticeable improvement in how the engine starts and runs if you put in some fancy miracle plug but that will simply be a case that any new plug is going to work better than a 3-4 year old worn plug.