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I have 10.8 to one squeeze in the 493 in the Charger. Edelbrock aluminum heads, MP '509 cam. Performer RPM intake, BG 850 carb and TTI headers. I'm also limited in my advance timing. In my case, its 30-31 degrees. I've been running Champion RC12YC plugs as per the Edelbrock instructions. I have a set of RC9YCs, but I have yet to swap them in. Several members here have suggested colder plugs for my detonation issues. Its been unseasonably cool here lately, so detonation has been limited. I'll swap them in soon though. THEN I'll know if they helped at all.
I've wondered for years: Do you make more power with LESS compression and more spark advance ..... OR more compression and LESS advance?



You make more power with more compression and the least amount of timing. But let me explain my response. The less timing you need the more efficient your combustion chamber is. Notice I said "need". If your engine needs less timing because it's detonating, that doesn't make it an efficient chamber. I built a 360 with magnum R/T heads. Pistons come out of the bores between .003" and .005". .039" head gaskets gives me a fairly tight quench. I was running 39 degrees locked timing because it started fine and I didn't have access to a dyno. Well I finally put it on a chassis dyno and started playing with it. Dropped the timing and it made more power. Finally settled on 34 because I didn't think it'd ever like less. Yanked the motor out to freshen and put it on an engine dyno exactly as it came from the car. Finally made best power at 31 degrees. Proper quench and a good chamber make great power. It never even attempted to detonate that I could hear and there were no indicators upon teardown that detonation was an issue.
Finally built a 440 for my truck. KB flat tops that come out .007-.009" 452 heads and piston to head clearance average about .110" This engine made best power at 38 degrees total. Well, that's where I stopped anyway. My elevation is high enough that the compression isn't an issue. Running cold NGK plugs (can't think of the number offhand) They will load up when it's cold, but once the engine is up to temperature and cleared out, it runs fine.
Ideally, I'd have quench type heads (preferably Victors, Indy or Brodix), pistons that were out .003" and a dyno to sort it all out with. Other than that, all you can do is start at the beginning. Throw in a colder plug. Go extreme if you must and go warmer from there. Keep the timing at 28 degrees and no lower. That'll save your exhaust valves from overheating. If it still detonates, verify your cam timing. Do you have the 108 lobe separation cam or the 112? If the 112, that could be part of your problem. What jets, exactly, are stage 2?
Might be worth taking it to a shop that has a chassis dyno and paying them to sort it out. Make sure they have the equipment to test it with O2 and all that.