I see head gaskets with many bore sizes for Big Block engines.
I've been told that sometimes, the wire ring in some gaskets can lead to detonation if they hang into the cylinder bore. I have a 4.35 bore. The popular Fel-Pro .039 thick 1009 or 8519 has a 4.410 bore. They also make a .051 that has a 4.590 bore.
Is there anything wrong about using a gasket with a bore size that large? Are you better off using a gasket closer to your actual cylinder size?
Cometic lists some MLS gaskets with a 4.380 bore. Obviously this is about the closest I could go. My thinking is that a larger bore gasket would help in my efforts to lower compression.

Do you have stealth heads? I believe the problem some had is with these heads. The earlier ones weren't machined properly & the gasket would hang into the chamber. I believe the felpro marine gasket was a cure. I think they fixed this issue with later heads.

Just flip your heads over & lay the gasket over them to see if you need to look for a different gasket.

Yes as you know you wouldn't want the fire ring to overlap the bore. I'd want the gasket to be as reasonably close as possible just for more gasket support area (I aint' sure how critical that is but that is my thinking). yes you lose a slight & I mean very slight amount of CR with a bigger bore gasket. Get on the KB site & plug in some numbers & you'll see. By the way have you computed your actual CR? since people have opinionated that something else is going on with it pinging at your stated CR. I think it's just crap gas & too high of SCR & reportedly left coast gas is the worst & people in the gasoline industry have reported that octane levels vary all over the place & quality control is terrible & ain't nothing like it is touted up to be. Post all you want, it's a free (no limit) site & if people dont like it they can ignore anything that is bothersome & just me I'm OK with it. I say get a conservative cam in there that suits your driving parameters/ drastically lower the CR either with a way thicker custom Cometic gasket OR with chamber and or piston deck material removal then a .017" custome Cometic gasket to maintain your quench . I've got a bet going on with this for what it will take to fix it. EDIT meant to say .023" gasket since you are .017" in the hole

What heads?

Fel-Pro 1009 are a tight bore fit at 4.375" w/o any significant chamfer on the top of the bore.

Fel-Pro 8519-PT1 (standard replacement) and 17059 (marine-spec) are both 4.500" bores -- yes, I've measured them -- regardless of what the advertised spec is.

Using a head gasket w/ an oversize bore is NOT the best way to deal w/ reducing compression, because it creates a "dead zone" in the combustion process where the gasses get trapped, instead of being used efficiently. However, due to combustion chamber shapes & overhang issues, it is an option.

In every instance except the one time I tried Cometic gaskets, I have used the standard Fel Pro gasket that comes in the full gasket set. I thought that it was the 8519.
I'm using Edelbrock heads. They are supposed to have an 84 cc chamber.
I have used several online compression calculators and I keep coming to the same number.

Bad gas in California? I can't say that I know how consistant the octane is from day to day, pump to pump, but I can say that the higher octane does exist. My 2007 Ram does run stronger on 89 compared to 87. The Charger ran fine on 89 with my first 9.2 compression 440.

Running 20 degrees total timing did not help you, the tune on that motor was part of what was causing it to detonate .

Maybe I was not clear.
I ran the engine at 16 initial, 30 total and it detonated at just over half throttle. I retarded the timing while I was on the road testing it. It still knocked. I backed off the timing again. ( Again, just for testing purposes) It was at this third timing setting that the engine did not knock at WOT. At home, I checked the timing with my light and found that it was at 6 initial and 20 total. I had no intention of ever keeping the timing at this setting. I was just trying to see how far back I had to retard the timing to get the detonation to go away.
I appreciate your efforts and suggestions though. Thank you.

Too large a bore in the head gasket increases what engineers now call "Crevice Volume"

Another major source of Crevice Volume is at the ring land from top of piston crown to first ring.

It has only been over the last 25 years that experiments have proven that Crevice Volume is the main reason part of the fuel does not get burned, which leads to power loss, lower fuel economy, and increased CO and HC emissions.

There is a persistent Myth that fuel does not get burned because the carburetor does not make the droplets tiny enough,
aka the 200 MPG Carburetor.

The truth is that Crevice Volume is the villian
in keeping 5 to 9% of the fuel from burning
in the first 15 degrees of crank rotation
where the good leverage arm ratio leads to
peak power and efficiency.

Very interesting comment/fact on the 'crevice volume'.
I learn something new everytime I come here.
I have gathered over the last year that indeed it is critical to A)not have the gasket fire ring overlap into the chamber as it will erode and eventually fail, and B)now I see it is equally important to have the gasket fit near'perfect'to the block and head combo.
One thing I am a little puzzled by is I always thought alloy heads allowed a little more compression ie. better heat dissipation and also 'cushioning' the crank mains a bit lessening the pounding they would take with a more rigid iron head at the same compression (not that those 2 things are related, just sayin').
Not that that would crutch bad gas or other related issues...
Could the timing be coming in waaay too early down low and contributing to this?(and/or maybe a part throttle lean out?)If this could not be solved with a conventional dizzy,maybe a programmable timing curve box?
I also did not know what Cab said about even minute oil contamination causing detonation, but it makes total sense.
Lastly,Franken,your pics to my eye show NO long term det. It would manifest, as others said, as a 'craters on the moon'look.Thank god you stopped before it was too late.

Bear

Thanks, Bear.
I never thought about "crevice volume" either. Yesterday I laid a Fel Pro head gasket I had from a full gasket set onto the deck and found that the chamfer at the tops of the cylinders actually was wider than the fire ring. This may have contributed to the knock.

the tricky part to Crevice Volume
is understanding how
a tiny crack
can get packed with
5% of the air and fuel

when the piston reaches 35 degree before Top Dead Center
the pressure of the un-lit air and fuel is 140 to 200 psi depending on dynanic compression ratio

but when the sparkplug fires
pressure begins rising rapidly toward 1000 psi or more

this ball of outward moving pressure from burning
"pushes" fresh unburned mixture deep into the Crevice Volume

the cool metal walls surrounding the Crevices
"quench" this momentarily highly compressed mixture
and keep it from combusting
until the piston has dropped far below the 15 degrees past top dead center where pressure on the piston produces good torque

Crevice Volume in engines is highly undesireable

Crevice Volume in coal mining electrical equipment
is one of the greatest "Lifesavers"
ever invented and "quenches" explosions that happen inside equipment electrical boxes and keeps these unavoidable interior explosions from killing the miners.

Methane gas will always seep inside the electrical boxes along with air, so this accepted and the boxes are not made "airtight" on purpose. But sufficient crevice volume is designed into every joint to quench an explosion that starts inside, and the walls of the electrical boxes are massively thick steel compared to common electrical boxes.

Mine inspectors routinely slip feeler guage blades into these joints to make sure they are neither too thin or thick.
Too thin and the box becomes airtight and bursts from internal pressure.
Too thick and the quenching does not go successfully and even a small spit of flame can initiate a mine air explosion.

good stuff 360view