Adam, I'll give you my version of plugs since I sell them and have worked with them for years. Our standard plug in the Delorean is the: HR6 HR6, Cold plug,, More for long drives and not short hops. Will carbon up faster because the plug doesn't have time to heat up and burn off contaminants. HR7, Little hotter, Better than above. HR8, Medium range, Bosch Platinum + 4 also medium heat range. This plug will heat up faster to burn off the contaminants, and better if your burning a little oil. Due to the least resistance will perform better at idle and running of the car. HR9, Same, hotter plug especially if your burning a little oil. HR10, Hot plug, could cause preignition, but will burn of oil and contaminants best. To me, Plugs should be tailored to your normal driving habits and the age of the car. I have charts on the web site about plug burning and heat temps if you need more info. John Hervey www.specialtauto.com << Can anyone who has used these plugs give me their opinion of them? I am doing a tune-up soon and am thinking of using these plugs. Also what heat rating do you suggest for an engine with 75,000 miles on it, is it different for the platinum plugs? thanks for all input! Adam >>