Canadian Mustang Owners Club - Ford Mustang Forums

More on plugs from MD...

First off the material of the spark plug is very important. Platinum is bad, copper is good. The OEM's use platinum for two reasons. If the plug were to wear out in the emission warranty period then they have to replace them under warranty, this is money. Second, there are a few groups out there that track cost of ownership of vehicles. If you recommend spark plug replacement at a certain interval, then they include the cost of doing this in their ownership cost when they put them together. If some company, like Hyundi, offers a spark plug that only needs to be changed every 100k, and Ford says every 50k, then the cost of ownership is less for the Hyundi (I know I spelled it wrong but I"m an engineer, cut me some slack). This ownership cost gets read by people and OEM's. If you think it's not true, how many older people like me are there out there that remember when tie rod ends and ball joints had grease fittings? Now they don't, why? I bet Randy (the Ford parts guy) will tell you he has looked at greased vrs non greased tie rod ends and he thinks they look the same to him, and they are. Ford use to recommend to grease the fittings every oil change. This cost of grease and labor was reported in the cost of ownership study and in a year, Ford removed the grease fittings because GM had....

(now I know this last section is way off the topic of spark plugs, but it's kinda important).

So, copper is a much better conductor of electricity than platinmum, but it does wear out sooner. Use a copper plug and with an N/A replace them every 15-20k, 5-10k on a blown car. Get over it, going fast costs money. If you want your motor to run well all the time these things must be done.

Heat range is good one.

First off, due the huge difference in combustion chamber design, what works on a 4V may not work on a 2V and vice versa. The 4V chamber is very efficient and you can end up with too cold of a plug. For both blown and non blown applications for 4V's, I'd run a 22C plug. For an N/A car I'd gap them about .050" and a blown car in the .030"-.040" range depending on boost. You want to run the largest gap you can and not have spark issues. A larger gap gives a more intense spark.

On a 2V, I'd go with a 22C at .050" on an N/A car but I'd go with a 12C on a blown car with a smaller gap. The 2V chamber is not as efficient and you can help surpress some detonation by using the colder plug (the 4V chamber does not respond this way to a 12C).

Now, if someone was paying attention, they'd ask why an '03 Cobra uses a 12 heat range plug then. I'd ask, how many plugs and cats has Ford replace under warranty on those cars due to plugs fouling out....

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Sound familiar???