Hardened Valve Seat?

From the internet:

1. Slant 6 Engines:
   • The slant 6 engines received hardened valve seats around 1970/71 when leaded fuel was becoming less available. These seats were introduced to handle the transition to unleaded fuel1.
   • However, it’s worth noting that some experts believe the original 1960s Mopar seats were already harder than those found in Ford or Chevy engines of the same era. In fact, they argue that even today’s replacement seats are no better than the factory-installed ones from back in the day. So, unless the seats are damaged, there’s usually no need to upgrade them1.
2. Catalytic Converters and Unleaded Fuel:
   • The widespread use of catalytic converters in automobiles demanded the use of unleaded fuel. Consequently, Chrysler started incorporating hardened valve seats later, around 19751.
3. Other Notable Instances:
   • Cylinder Heads (1971): Various cylinder heads, including the 346 casting from 1971, featured improvements such as hardened valve seats for durability2.
   • 1946 Town & Country Hardtops: Chrysler built seven Town & Country two-door hardtops in 1946, the same year they claimed credit for a hardtop convertible. These cars also had hardened valve seat inserts3.

In summary, Chrysler’s adoption of hardened valve seats varied across different engine models and years, influenced by factors like fuel availability and emissions standards. While they became more common over time, the original Mopar seats were already quite robust