They are one stage colder than the the factory heat range, and they do a pretty good job on my car (I run a little more boost than most with bpu). One thing I have noticed 'though is they don't like leaded gas (ran a tank of 118 octane gas in the car.....bye bye plugs). they were permantly destroyed. Couldn't rev over 4K without misfire. I figure if I ever want to spend big money on gas again 'though, I will just swap out to copper plugs.