70 cuda 4 speed 3.54 gear 440 6 pack Mopar 484 cam, Hooker Super Comp headers. I feel the combo I have now is not very detonation tolerant, I have fattened the mixture and run colder plugs and can still not make it take more than 28 degrees total without the plugs looking like porcupines. Currently has 452 heads with KB 237 Silvolite pistons. With the 88 cc chambers and the piston .010 in the hole and a 5 cc valve relief, this gives me 9.7 CR.
I am considering using the Source 440 aluminum heads with a closed 80 cc chamber. If I swithched the heads only, my qeunch would be about .050 ( gasket + .010)much better than what I had with the 452"s (is .150 even considered quench??) but boosts CR to about 10.5 which even with the aluminum heads I feel I may be back in the same situation. I have heard aluminimun heads are worth a point in compression but even if thats true my true effective CR would be 9.5, not much less than 9.7.
KB makes a forged piston with a 12cc dish which would give me 9.6 CR with the 80 cc chambers and I couldalways cheat with a gasket .010 or so if I wanted, or I coud get the heads milled a bit to get it up some. Not looking to build a drag engine or something for max power, just looking for a nice running engine that I don't have to worry about detonation. Any thoughts. I realize I am looking at about 2k to do this I just can't endure the clatter and the consequences anymore, who knows, I may be able to lean it out a bit and/or run a hotter plug to keep things cleaner. BTW jetting is "stage 2 as per moparts forum guy (very helpful) not sure what the plug is but reccomendation came from the same source as the jetting. SO what do you think??

I had a pretty bad detonation problem with my 512 stealth headed motor 11.3:1 comression. I changed the power valve from a 3.5 to a 5.5 upped the jets by 4 dropped the heat range on the plugs down 2 and got the corn ( ethanol) gas out of it and put pure gas in it. The detonation problem went away. I think getting rid of the corn gas and putting the colder plugs in it made the biggest difference.

"Stealth Headed" are those aluminum? I hate corn too. Are your heads open or closed chambers? Piston style???

The change may take you from "beyond the ragged edge" to the ragged edge. With a moderate performance cam, I always figured 9.5 was max with iron heads and little to no quench. You are higher than that "rule of thumb" with your current setup. With Al heads, 10.5 is max. You would be right at that figure with better quench to help.

The upgrade to Al heads/10.5 CR would help but enough? I don't know. If you could use a small dish to get in the low 10's I would say no problem.

I agree, with the closed chamber heads I could check piston to valve clearance and then mill the heads to get 10 or so. According to the CR calculator I would need to heads down to about 77 cc's to get an even 10. Not sure what that means millingwise but might be possible. Sorry I misread the compression height on the 12 cc pistons so I would get 9.833 with the new heads and the 12 cc dish pistons and .050 quench.

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?

I'm sure there is a balance somwhere, seems you would make more usable power without the prescence of detonation since the plugs and combustion chambers should stay cleaner (hopefully).

Have you thought about running aviation gas?

Throw a Snow water injection system on it.

It's likely the open chamber (no quench) causing the problems more than the compression.
Wayne Smothers DVD on how to supertune your engine talks about the same issue. It is no so much the compression ratio, but the open chamber is allowing multiple flame fronts which collide causing pinging.

Link to Video on Amazon:
http://www.amazon.com/Performance-Engine-Building-Carburetor-Tuning/dp/B002QWJ1DM

Yea the 440 source heads are stealth heads and they are aluminum closed chamber. I don't remember what "piston style" I have

Cheapest easiest fix it to run 85% corn fuel (E-85) you will make more power and contrary to the guys bashing it on here it help control detonation NOT cause detonation. There are lots of guys running 15 or 16 to one on e-85 with no problem. When I am in OK city visiting my folks I use it in my cars, it is every where down there. I ran it all the time in Tennessee and I wish it was available here. It also carrys more oxygen with it so you can richen up the mix and make more power with no engine mods nessacary so it is way cheaper than tearing you engine apart and replaceing heads and pistons.

Do you have the vacuum advance on the distributor connected ?

You are a little light on max timing advance and that may be making the problem worse because your running a little hot ?

.050 is the edge or getting the advantage of quench , what you have now with the 452's is nothing .

First, you have not told us what plug you are running. There is no reason with that compression you should not be able to run a NGK XR5 type heat range. Something elso is not right here.

What is your ignition system? In order run more advanced timing you need to make sure you have a good ignition. I would start there. I had a very similar combo and actualy had 10:1 with 452 heads and ran 36º total timing.

That MOPAR cam is not helping you out at all. I would consider a change to more modern cut like Lunati Voodoo.

i think its your tune, i run 11.2cr with j heads and 205 cyl psi on 93

that 484 cam should be bleeding a good amout of cyl psi, you have your heat crossover blocked correct???

It is useful to know which of the eight cylinders is detonating.

The inexpensive 'Fires in Oil' sparkplug extension sleeves can be used to find which cylinder is the most prone to pinging.
The extension sleeve has an effect like retarding the ignition timing in that particular cylinder,
plus it adds a couple cc's to the combustion chamber, which slightly drops compression ratio.

Another trick to narrow down the source of detonation is to temporarily use 2 cycle synthetic oil.
This more expensive 'ashless' oil has a much better 'blending' octane rating that 4 cycle oil,
and if the pinging goes away on a test drive with the 2 cycle oil in there, it indicates an oil control problem in one or more cylinders.

Since you are still using a conventional distributor and cap,
once you find the troublesome cylinder(s) it is possible to modify the interior posts on the cylinder cap to retard the ignition timing cylinder by cylinder.

As you approach the 'ideal' ignition timing for a cylinder's performance,
called the 'Mean Best Torque' or MBT timing,
you will find that there is about a six degree span over which torque does not increase or decline... kind of a flat plateau instead of a sharp peak.
The timing needs to be on the 'retarded' edge of this plateau, because unlike torque not changing,
detonation likelihood increases even faster with ignition advance as you approach the limit.