Just fill it up with 87 at the halfway point and you'll end up with 89 octane or so. If it doesn't knock or ping, you're great. Keep doing that and you'll eventually end up with 87 octane in the tank. If it isn't knocking under load, you'll be saving 50 cents a gallon or more. $10 per tank or so.

1950 Chevrolet 3100 (Ol' Roy)

1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)