a plug is supposed to run at a temp between 740 degrees and about 1700 too "hot" pre detonate, and you'll burn holes through your piston, too cold and you wont burn all the carbon, and foul them. The reason for different plugs is for that reason, and a 'cooler' plug has a shorter electrode so it cools faster, a hotter plug has a longer electrode so it retains heat. IMO i'd upgrade the plugs to platinums and forget which are hot, and cold, and use oem ref numbers. but, that's just coming from a guy who builds 2200hp snowmobiles.
