I've been looking around for colder plugs for our application. Dyno guy turned me on to that overlooked detail in my 11.2:1 compression motor as a possible fix for my knock/timing problems.
Here's what I've learned about heat ranges: a colder plug will cool faster, thus preventing pre-ignition caused by an overheated plug at high throttle. However, its operating temp will be lower, and if this goes too low it will tend to foul as it will not clean deposits from the air/fuel charge and combustion at low throttle settings. Unless you are bumping compression or chasing a knock problem (like some people have seen on the +4's), there should be no need for a colder plug in our motors.
The specs on our plugs (from autolite.com for APP764): 14mm thread dia, .708" reach, 5/8" hex head, tapered seat, power tip, D14 heat range (dunno if D14 is some sort of standard or and Autolite reference).
OK, so I looked around and found a big Excel cross reference sheet for all spark plug mfg'ers. a little old, but it did have the AP764 listed. As far as I can tell, the plug spec'ed on the Duratech (both 2.5 and 3.0) is the coldest standard part offered by the plug companies in that form factor.
NGK appears to offer a racing plug (called a street/strip use plug) that may be colder, but it is not platinum, it is a nickel electrode plug. I'd have to change them every 12k or so. Not sure if I want to get into that or not.
Another thing I've learned is that higher compression requires smaller gap, so I'm going to try something a little smaller than .054". Any suggestions?
I emailed NGK and Autolite looking for a colder plug than what they call out for the Duratech, but no answers yet. Any spark plug/engine gurus have some help for me?
