My 518 C.I. low deck stroker motor with 15.0 to 1 compression liked Autolite #3934, it did NOT like any colder plugs whiney You can try those colder plugs but don't surprised if the 3934 or 3935 will work better twocents
Those Autolite racing plugs have a retracted gap and seem to last forever with our local pump E85 up scope

Last edited by Cab_Burge; 07/28/22 12:49 PM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)