http://answers.yahoo.com/question/index?qid=20080410101759AAEk8ou Hopes this helps,,, 42 is colder than 44
I had actually done my google search and read both of those. The "people" say (the general consensus is) that the lower 2nd number corresponds to a cooler plug, but the description from AC Delco does not clearly state that... So, this just confused me and I figured someone on our forum would know. I am guessing that "numeric code" means the 2-digit code, and the second digit still means hotter when higher, when compared to other plugs with the same first digit. I went ahead and bought a 44 and a 42 and am running them both on #1 and #5 cylinders, and will see if one colors differently than the other. So far, both are getting a nice light tan color to them, but I haven't driven yet, just run it in the garage.
You would be a lot happier with Autolite plugs. AC's, in my experience don't last as long or work as dependably as the Autolites.
I have not found Autolites that fit this head. They make the platinum ones, but no cross reference to a copper set (AP764 is the platinum model, could not find the non-P 764s). Also tried Motorcraft, but finally got tired of dealing with the parts counter associate and just took the AC Delcos I know fit. They never were able to successfully order the Accel P526 plugs that the engine worked so well with before.
I got rid of the P heads and now have regular GT40 heads. I sold those "special" plugs a few weeks ago to someone using P heads. The regular GT40 heads will accept any regular old plug, but it is a different size around, and deeper, compared to the stock heads. It just doesn't have to be those $18 each shorty plugs.
also check out the ngk line of plugs ive heard good things about them and have used them on my old 5.0 mustang with out any problems.
