valves rattling

i noticed when i run 87 octane in my brothers 86 ta
the valves rattle under heavy acceleration.
if i run 92 or 93 runs just fine, why?
it's $ 2.03 a gallon for 92 octane were i live.
does it need a valve job or is it just the
gas watered down.

That's not valves rattling, that's detonation or "pinging". Use the better gas and tune it up. Was the timing ever advanced on the car?

Your engine is detonatiing. it requires the higher octane to resist pinging. make sure your timing is set ok.. not advance too far. can try water injection. water injection cools the incoming gas air mixture.

yeah its a 86 trans am 230,000+miles
but the engine locked up. the oil
pump quit circulating the oil.