Are there any problems using unleaded 87 or 89 octane fuel in a '74 C3 (base engine)?

 

Hi j6,
Since the base 350 engine in 1974 had a compression ration of 8.5:1, either the 87 or 89 octane would be fine.

To some degree the timing comes into play here too in order to prevent 'pinging'.
Regards,
Alan

 

I ran cheapo unleaded in my 74 L-48 for years without any problems.

 

Ditto for me. However, not that many gas stations are including ethanol, I am starting to wonder if I should be more picky.