NGK's lookup table recommended XR5s for a '67 GTO. it's a 13/16 gasket seat, projected tip, seems legit? Cross reference charts show it to be equivalent to R44S or Autolite 85, so one heat range cooler than R45S, right?[/QUOTE]
Right
AC plugs get hotter as the numbers increase
NGK plugs get colder as the numbers increase.
The standard AC plug is a R45S gapped at .035 for a ‘65 389.
The NGK equivalent of a AC R45S is XR4which I use and will continue too in my 389
I’ve used the Autolite and Champion over the years and found both to be inferior in my combo.
Mike
|