ok i have a 96 camaro 3.8 that i tore apart and out back together i started it and when i reved it up it would knock real hard but only once and when i would rev it up real slow it wouldnt knock but then again i would punch the gas hard and it would knock real hard again.. i was thinking rocker arms or head bolt broke or something any help i appreciate it thanks..

shawn

 

If the engine is freshly rebuilt, why are you hitting the gas hard?

Its possible to be the things you mentioned. It could also be detonation. Your description is a little vague. Without testing equipment it may be difficult for you to locate the problem yourself. The air-fuel ratio should be monitored. Fuel pressure, timing etc.
Are you throwing any codes?
Unless pinpointed, a knock could be anything from valve lash to a loose connecting rod! If you have one, or can make one, use a stethescope and attempt to find if its coming from above, the combustion chamber, or below it. And which cylinder(s).

 

i just pulled the heads cause i cracked mine and i bought junk yard heads without taking them to the machine shop, (another reason i was thinking..) could wrong torque on the rocker arms make it do that???

 

cheap repairs lead to expensive repairs.

 

If you can make it knock under no load you can start it and put your hand on the engine. Then hand activate the throttle and you can at least learn how hard the knock is and where it is coming from.