http://www.ngksparkplugs.com/tech_suppo ... p?mode=nmlThat link basically gives the differences in heat ranges explained. Overally at low end your better off with a more cooler spark plug as apposed to a hot one especially in our climate also too the higher heat range/cooler plug actually reduces engine temperature.
Factory SR20s come 6 heat for a reason as well as OEM plug wires is the best plug wires you can get (other than Magnacor or a external coil vibes)
Reason I put this post is because you would be surprised the difference in types of plugs can cause....I decided to go 5 heat with original NGK plug wires...car idles rough...it has a jump in accelerating in 3rd gear. Compared to the 6 heat with new OEM wires it failed...
