My 68 302 is currently running an Autolite plug that says its for a newer 4.6 motor. Any idea why the PO would run this?? And what type do you guys use?? And what advantage to running a warmer or cooler plug?/

Thanks

 

No idea,, but I would also like to know.. and what gap size do you use if you put a warmer cam in?

 

The original plug was a an Autolite BF42, which converts to a modernAutolite 45. I'm still running these in my built 331 and they work fine. If you're getting some oil blow-by and foiling the plugs, or if most of your trips are short and part-throttle andyou're getting some fouling, the next stage hotter would be better for you.

Gap is going to depend on what kind of ignition setup you have.

 

The exact plug number is Autolite 5143, and when I looked it up, it was for a 05 to 07F/I 4.6 motor??
My 302 has an MSD ign, performer intake, edelbrock carb and roller cam......any reason he would have run these plugs??

 

I'm running Autolite 24's but I'm also using aftermarket heads, not the stock old school with those monster fatty plugs.

Heat range is basically about heat conduction. A "hotter" plug has a higher heat range, this means it has LESS insulator material and conducts heat into the head more slowly and in smaller amounts, causing the portion of the plug that is exposed to combustion(the electrode, ground, insulator etc) to be hotter(hence a higher heat range). Colder plugs have MORE insulator material and as a result transfer more heat away more rapidly and consequently the portion of the plug exposed to combustion remains cooler. You want a plug hot enough to provide stable, consistant combustion and be able to burn deposits off of the plug, yet at the same time be cool enough so it doesn't become a hot spot and cause pre-ignition/detonation

 

Great explanation 67 mustang! The stock 60's 289's run a BF-42 gapped at -.032- .036 and the hi -po's ran a BF-32 gapped at .028 -.032. I believe the lower the number the cooler the plug (when it comes to AC and Autolite)

 

I use Autolite platinum 45's , I am haveing great luck with them

 

Any idea why the PO had the plugs for an 05-07 in there?/ Are the BF 42's a large base instead of the peanut type of the 5143???

 

I am running plugs for a late model Dodge V-10 in the Vic Jr. heads,,,,

There was a Champion number in the instructions, but it led absolutely nowhere,,,,

I forget just how I arrived at this selection, but so far so good....

 

You need to go with the Autolite 45's or Motorcraft 420 , you will have better luck with the right plugs for your engine