What type gas goes in 71 grand prix?

Do you happen to know the compression ratio on you engine? If it is more than about 9:1 needs premium, the high compression engines need a higher octane because it has a lower flash-point to ignite, Supercharged cars also need high octane for same reason, the positive pressure in the intake, opposed to vacuum, (a supercharger forces air in to the intake instead of the vacuum created when the piston travels down with valves closed, then the intake stroke does not have to suck air in, its pressurized--- actually only a little bit -- will not ignite and burn properly with a high flash-point fuel

Engine choices included the standard 400 CID V8 with four-barrel carburetor and dual exhausts, rated at 300 hp (220 kW); and the optional four-barrel 455 CID V8 rated at 325 hp (242 kW). Both engines received substantially lower compression ratios (8.4:1 for 1971 compared to 10.25:1 in 1970), so no. Regular is fine. In 1070 it was not