Autolite 65 would be a stock heat range, stock configuration (13/16, extended tip, 3/4 reach) plug. Go to 64 or 63 to go colder.

This crosses to a BPR5ES NGK. Those are the only brands I would consider.

The 5/8 hex is an Autolite 3924 which goes to a BCP5ES if my memory is correct.

Champion? puke

Last edited by CMcAllister; 04/25/20 10:19 PM.
If the results don't match the theory, change the theory.