Best spark plugs for 21 studs

[Reds34]

Hi all,

What spark plugs do you guys recommend for 21 studs engines with 18mm plugs? I'm chasing issues and curious what you all use for spark plugs.

Thank you for your help.

Red

 

[Lawson Cox]

Champions is what they came with.

 

[Jack E/NJ]

Google search 40-12405 for vendors. Champion or AutoLite.

 

[CA Victoria]

Autolite 386

 

[Bill OH]

I used Champion 7s in the mid 50s, but I think ??? Champion D16s will work.