Hot Rods HARDENED SEATS ???

I guess to figure that out, you'd want to know when they went to integral cast seats. Then, when they switched to induction hardened seats (which from what I've read, happened mostly in the early 70s when unleaded gas became available again)

 

I wondered about that, if the usual "top oil" treatments such as MMO help. There are others.

 

as far as I can tell, the hardened seat were on most HD applications

most manufactures use them in their HD truck engines
early, before the lead was introduced some manufactures used them
around 71 most manufactures started induction hardening the seats to meet the unleaded GOV demands

 

an old man once said to just add a little diesel fuel every time you filled up
but who knows