I do hope that all of this stuff ends up helping others as well as myself. I have read archived threads on this and many other subjects in the interest of learning.
My understanding is that while Mopfried has a good point about the bigger cam making more cylinder pressure at high rpms, maybe the short time span at that high rpms makes detonation less likely??
Don't worry about anyone thinking your post was hijacking anything. I am open to all points of view.

Anyhow....
I found a Dynamic CR calculator that has that odd "Intake closing PLUS 15 degrees" bit:

https://www.uempistons.com/index.php?mai...e30f95974e64ff7

Using that calculator, the '509 gave me a 7.91 Dynamic ratio. The Lunati gave a 8.09. I was told that a dynamic at 8.0 or below was good enough for pump gas. Maybe they mean 93 octane?

You are on to something. Reduce the peak torque area pressures and you might be ok on pump gas. Don't compare a street mopar to a 10,000+ rpm formula 1 engine.LOL build the correct comp(for the fuel) and then the balance of the build to make a good result. It's not that hard to do.

How did you arrive at 10.73:1 compression? Did you actually measure/CC everything yourself? I ask because when I plug in the numbers for a flat top 493 into my calculator with an 84 cc head, .039 1009 4.410 bore gasket -4cc valve reliefs and -.017 deck I get 10.86:1.

The Ross pistons in my 493 were advertised as being .017 in the hole but it only took .007 to actually zero the decks on my '76 block so in actual fact the pistons were only -.007. Now you are at 11.04 if your block was similar. At zero deck you would be at 11.29:1.

I didn't catch all the details on your build so if all this stuff has been already verified and I mean measured by you or your machinist and not assumed because of something wrote on the packaging, I apologize. But if you bought the heads used for instance and assumed they were 84 cc because the PO forgot to tell you he wacked them .060" it would go a long way to explain why your engine is acting like it has a 12:1 CR.

Kevin

I cannot help to think that possibly there are still a couple pieces of mis-information that keeps this thing going in circles. My opinion (I think ) is that you are on the edge with this combo being pump gas friendly, but have believed up to this point that you could get there by tweaking the details.

2 1/2 exhaust is not the problem, unless it has a failed muffler, but some one already brought this up and you concluded that this was not the problem.

When you get to the point (may be there now) that you just want to fix the problem, or symptom, here is my suggestion: Take the heads off and have someone with a cnc program (like MCH) cut the chambers to the desired cc's, and put it back together with the 0.027 gaskets.

I am currently considering a few options for head porting. As soon as I find someone I trust, I'll dig back in.
I am hoping that the porting and additional spark timing will more than offset the slight loss of compression.

I have been following this thread from the beginning. Reading every post every idea and watching for results from those suggestions.
The one suggestion from SUPERBEEDAVE asking about cam timing was the only one that I feel was not addressed/double checked.
I am not a know it all, or a done it, seen it, sailed it, scaled it, dove deeper come up dry guy.
But I have seen the result of a cam installed improperly timed.It ran soft down low had crappy idle characteristics pinged until higher in the rpm range then it ran unimpressively. Oh it needed premium fuel at 4500ft elevation at 9ish compression. Exhaust would glow, required weird jetting and timing settings.
The timing set was an edelbrock set their markings are vague as are the directions.
You have stated this is your first serious performance build perhaps a mistake in cam degreeing has you here. This is not a slam nor me criticizing you your efforts or anyone else's. Just trying to help. Some have said your engine is defying normal logic that logic applies if valve/cam timing is correct if not??? Who knows. Good luck.

The comment on verifying the actual cam timing and intake lobe seperation reminded me that it is so critcial it should be made mandatory on all cam instruction cards I have had the misfortune by stupidly aligning the dots without verifying the cam location, to find out that some cams and timing sets are not what they should be There way off My first roller cam install I aligned the dots and went through a lot of problems with that motor and dealing with the cam maker, Sig Erson in 1972, to resolve it.I found out later the cam dowel was off 10 degrees retarded, most Mopar motors hate having the cam retarded OP, I agree that you should take both heads off again and check all eight pistons deck hieght I've seen stock rods vary .009 in length in the same set That was on a set of 1963 M.W. rods, the lowest piston was at -.026 and the highest one was at -.017 (do the math on one hole with varying the deck hieght .009 to see what the compression ratio changes) Lots of gremlins out there, Mr Murphy loves jinking hot rodders Trust me on that from personel expereinces with cars and motors, let alone peolpe and parts One thing you should keep in mind is that most things that don't work properly and don't make sence the way they are operating have a reason for those results Stick in there, you will find it

i have never had a roller cam and chain set up that was anywhere close dot to dot.

Thank you for the suggestions about the cam timing.
This was my first time degreeing in a cam myself. I watched several youtube videos, asked questions here and on other forums and read what I could find elsewhere. I wrote elsewhere in another post that I was having trouble getting the degree wheel and crank turning hub to stay in position. The hub I was using had a loose fit on the Woodruff key and it allowed some slop. I finally just pulled the hub off and bolted the wheel directly to the crank using the dampner bolt. From there I found that the dot to dot marks actually did result in a 106 centerline, exactly what was called for on the cam card. I have the luxury of leaving the car idle where I park it. I am lucky that I don't have to be in any hurry to get it back together either. It certainly is not my daily driver!
While I have the heads off I can make a piston stop to lay across the block deck surface to check TDC on every hole. Wouldn't it be odd to find that I have 8 different compression ratios?

I should have mentioned that I actually have built 3 other 440 engines. THIS is the only one with aftermarket rods, a longer stroke crank, aluminum rocker arms and a solid lifter camshaft.

I've seen .003 differences in deck hieghts on the worst to the best on one motor using good aftermarket steel rods and very good race pistons with a good stroker carnksahft I guess nothing is perfect anymore BTW, there are several different ways to get confused on measuring piston deck hieghts I used to rock the piston over to the cam side of the block and measure off of the piston deck thier because that was the way NHRA would measure it with there dial indicator on a mag base when you got torn down for setting a record or winning a race I now rock them back and forth and measure both the inside and outside and then average the two to get a average deck heights I have seen .003 difference in change when measuring straight over the wrist pin location by rocking the piston forward and backwards from front side to back side Lots of varaibles out there

Get them heads off and have a look going with bigger CC gaskets

I got the right side head off of the car today. The head gasket looked fine. NO signs of any burns near the fire ring. The two long bolts securing the #8 cylinder seemed harder to crack loose than the others. No signs of any leakage, but then again there was no reason to find any. I had consistant compression numbers and zero external leaks.
I'll get the Left head off tomorrow and take them to my machinist on Wednesday. I may wait to order head gaskets until I know if the heads need to be surfaced much. If he needs to take .010 off to get them squared up, I may need thicker than the planned .075 head gasket to get the compression under 10.0 to one.

Cool less compression will help for sure.
Nice to hear no fire ring issue.

You should have them open up and unshroud the valves in the combustion chamber especially the intake, heads will flow better and material removed will help lower compression.

I got the left head off today. Looking at the head gaskets again, I found that while the fire rings were not burned, there were a few rough spots. I'm unsure if the detonation could have worn them rough or if they became rough, then the detonation began.
I have read the term.. Unshroud the valves before. Does this mean to clear material away from the valves to lessen restrictions?

rough spots on the gasket are likely from burning/glowing. Unshrouding the valve is opening up the combustion chamber around the closed valve where the combustion chamber wall disrupts the smooth flow of air into the cylinder.