“Catastrophic engine failure”
Give it a read.
His would run 2200-2300 and start missing.
Look at his pictures and see if it brings any “oh no” thoughts.

It wasn't acting/sounding like it was missing. It just was like it had no more power. There were never any backfires etc. Kind of surprising for how far advanced it ended up being.

Since you have the Thunderbolt IV what is the module number? It should be a v8-22 that will advance your timing starting around 1200 - 2000 RPM or possibly even lower(I can't remember the exact start of the advance curve). This module had 22 degrees of total timing advance. If you start at 8 it should give you a total advance of 30 at higher RPM. Can you run it up to/close to where it is backfiring and get a timing reading?

454 Mags use a V8-24 advance module

I read the catastrophic engine failure post. My engine sounds nothing like that at idle. Turned over fine on the stand and still does without plugs now. I have poly locks on my rockers set to 1/3 turn preload. I’m pretty sure I aligned the timing dots, not the zero on the keyway. BUT Is there any way to check to see if my valve timing is off without pulling the front of the engine off? To get the balancer off I would have to pull the engine again..... I really really don’t want to do that

- disconnected fuel line at carb, at idle it 1/2 filled a 2L bottle in about 15 seconds
- changed the fuel hose to tank.
-i can hear popping before secondary’s open. I can hear it in neutral, and didn’t want to rev it super high sounding like that. Secondary’s didn’t open in neutral, need a load.
-it has the v8-24 triangle ignition plate, have two and no change between them.
-SB I understand how the metering rods and hangers work to richen and lean fuel mixture, I was asking why they call it a Quadrajet if there is actually only two jets.
-I don’t have another distributor to try, gonna figure out how to check this valve timing first.
- I advanced and retarded the timing probably about 10° and it still popped, no real change besides idle rpm. Vacuum was it’s highest at 14.
thanks

Oh.Went over my head. Dimly lit. I don’t know.

I know you swapped carbs already but I'm wondering if the little fuel filter at carb inlet might be clogged. If some trash got into the fuel supply downstream of the water separator/filter it would wind up there on both carbs. Kind of a long shot, but easy to check.

Thanks Griff! I knew someone here would have the Advance curves.

Reg, get a timing light and test if you are getting any advance with the module connected. Harbor freight even has a fairly cheap one that has a dial on it to assist you with knowing where you are at. They aren't the best but they do work!

To me vacuum seems just a little low. Have you verified firing order and plug wire layout? I've personally seen an engine run okay at idle with the wires ran wrong (was told the engines were toast when I got the boat). Ran the wires the right way and it was fine.

Outside of this... 10.3:1 with iron heads and that camshaft is going to create a lot of cylinder pressure. I would listen closely for detonation and check plugs often. You're going to need to run premium fuel... always.

Could they have slipped you a 4/7 swap cam by mistake?

Easy to check. Swap plug wires for 4 and 7. You'll know right away.