273/235 Gas/Octane Requirements

I couldn't tell you why, but back in the 1980s the 340 that was in my GTS (stock 73 short block, 8.5:1) would ping on the mid-grade at the time. The 340 that is in it now (.030 1970 with TRW 10.5 pistons) never pinged on the modern premium, which is rated lower than the old mid-grade. Fuel mileage was lower, though...

Anyway, the point is that something changed and I just don't put any stock in the number on the pump as compared to decades ago...