Where's your base timing set? That could very well be the cause of your detonation. You should close the plug gap down some, too. I bet you're blowing out the spark. I don't think I have my NA combo gapped that wide. Someone with a S/C will have to give you an idea where to gap the plugs, I don't have one and I'd probably just feed you some misinformation on that, having no experience in that area.