I have a 455 that I had the short block built buy a engine shop. I just got the exhaust on and started it up and, KNOCK!. I heard what sound like a bottom end knock. The engine is new, the car is still being built so it has 0 miles on it. It has been run maybe 20 minutes total.
Where do I start chasing this down. I am hoping that it is not what it sounds like.
I put the rest of the engine together myself but the short block was all together.
Any ideas?

Also this is my first Pontiac so learning lots on this one. I also noticed once the exhaust was on that the intake has a opening where the choke goes and it appears to be open to the exhaust. I did not cover it because I thought it was a warm air channel only for the choke. Is it suppose to be a direct opening to exhaust. If it is can I just block it off until I figure out what out what is suppose to be there? What is suppose to be there?
Thanks for your help.
EB