Originally Posted by papagz

i just spoke to my mechanic today about changing the plugs. he said that it wont make any difference unless the car is running hot, or in hot temperatures. if your going FI then its a must b/c of the extra heat, but if your running mostly bolt ons, not gonna make a difference. he actually said it may even run worse...

Originally Posted by dklau33

The only reason to go with a colder plug is because your engine is creating significantly hotter cylinder-head or combustion chamber temperatures compared to stock. Extensive engine mods like forced induction or heavy NA engine work with high compression ratios will generate that added heat. So colder plugs are needed in those situations in order to draw away the added heat and regulate the temperature of the spark plugs firing tip. So don't think that just by adding colder plugs to a stock or mildly moded car will produce improvements. In fact if your plugs are too "cold" you will end up fouling your plugs in a much shorter period of time because the plugs aren't hot enough to burn off the carbon deposits.

Here's a pretty good article on spark plugs.

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