Just wondering. You would think the colder the better right?

 

The colder plug is more likely to foul during normal driving. Too cold is as bad (if it fouls & misfires) as too hot. Depending on your mods & what you are considering 3 ranges colder may be too much (what # plug are you talking about). The example plug, an NGK TR-6 is essentially 1 range colder than stock & has been used on some seriously modified engines with good results. I use these in most of my LT1 & LS1 blower motors. Do not compare heat ranges of different brand plugs as the cross reference leaves a little to be desired. An R42LTS AC plug is essentially 3 steps colder than stock, but works fine in the LT1 engine for most applications. Ironically this plug cross references to a hotter NGK TR-5 plug. These are more readly available in my area & also work well. General rule of thumb is to read the plug & see what it looks like. There are some good tips on NGKsparkplugs website. This will show you how to check the plug for overheating. Ultra cold plugs are great for racecars that only operate at full throttle.... but these applications are often started & warmed up on a different set of plugs to prevent fouling. Hope this helps.

 

6 heat ranges colder, no fouling problems with a Crane box and otherwise stock ignition. I do change plugs every season though (4-5,000miles)

Rich Krause