I just had my 350 in my 69 Camaro rebuilt. It was bored out with new pistons and rings and new cam. I have about 500 miles on it after the rebuild. When ever I get on it a bit at around 3500 rpm it starts to smoke. If I let up it stops. If there was something wrong with the rings wouldn't it smoke all the time? What are your ideas? Thanks for your help.

 

What rings did they use, and did you see the boring process? It sounds like the rings never fully seated, and under high pressure (like when you've got your foot in it) the rings aren't sealing. Were the heads rebuilt also?
Hopefully they did a bore job with a boring plate in place, and used the correct ring and hone to match each other. Each style of ring needs the correct grit hone, and crosshatch pattern to match that ring.

 

Go back to the rebuilder and explain this all to him... Hopefully he will stand by his work.