If it's a non Magnum, I'm surprised it doesn't rattle with 8 deg initial. I had a 69 Belvedere with a 318 many years ago and factory timing spec was TDC. If you tried to add any timing at all on regular gas, it rattled and that was before unleaded fuel.
Kevin
Same with my 68 Coronet with 318. Factory timing for my 68 was 2 1/2 degrees ATDC, that is stated on the green tuning spec sticker on the fender. It actually runs good and no pinging with that timing.
However, I keep it set at TDC, but if I set it to 5 degrees or 10 degrees BTDC, the 318 pings and have to use 100 octane avgas to stop it from pinging. So I just stay at TDC on 87 octane.
