I have a 70 chevelle with a 350. I put in an HEI ditributor and my cam is 230/230 at.50 duration. I have a 750 edelbrock carb and have headers on also. I would like to know what the timming should be set at to get the best performance. I have it at 17 btdc right now and when I get on the gas it backfires. If I go any lower than 17 btdc it surges at stop lights.