1987 Chevy Corvette Engine knock

Noises problem
1987 Chevy Corvette V8 Two Wheel Drive 75000 miles

I have a '87 corvette with 5.7 liter TPI motor and automatic trans. The car runs and drives great. The problem is when ever I accelerate hard I hear a knock in the engine. But normal driving and acceleration its fine I hear no knock. I thought the timing might be off so I looked and adjusted it back to factory spec (wasn't far off). The knock seemed like it got a little quieter but not really, I still hear the knock under heavy acceleration. I run 93 octane gas always. Not sure if it has adjustable rockers and there out of whack or what could be the problem.