I recently rebuilt my 455 Olds and I'm not sure if I have a timing problem or something else. I'm not sure what any of the timing marks on the indicator are according to degrees except 0, but I have it set on the last notch on the indicator. I have been easy on it while breaking it in for several hours. Today, I was cruising at 3K rpm and decide to open the 4 bbl for a second or 2, I gave it about 3/4 throttle and at a little over 4K rpm as soon as the power hit, it started pop/crack/backfire. Where should I be on the timing indicator? I'm pretty sure it's a timing issue, but I could be wrong? Thanks for any input!