I have a 83 911 930 grey market it runs on all six cylinders but the cylinder on the left left back by the turbo is making a pinging noise I listen to it with stethoscope. I did adjust the valves to make sure that was not the problem And it makes what I think might be a chain noise when I shut it off it is lacking a little bit in performance hopefully not a broken piston not sure if anybody has an idea of what it might be please let me know thank you for reading this.

 

Could be a hundred different things, I'd take it to a trusted Indy who's familiar with these cars. Anything to do with the pistons or timing chains is indicative of needing a total rebuild. Budget 20k.
If you could provide more info or pics/clips I could provide a better answer.
Good luck either way!

 

You should post a video on youtube and put the video link here. You can use a laser thermometer(cheap amazon) on each of the headers to see if the exhaust temperatures are the same for each cylinder. That would help if it were a fuel or spark issue, but it sounds like your describing a mechanical noise.